pkg/front_end/lib/src/fasta/kernel/body_builder.dart - sdk.git - Git at Google

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.

 library fasta.body_builder;

 import 'package:_fe_analyzer_shared/src/flow_analysis/flow_analysis.dart';
 import 'package:_fe_analyzer_shared/src/messages/severity.dart' show Severity;
 import 'package:_fe_analyzer_shared/src/parser/parser.dart'
     show
         Assert,
         BlockKind,
         ConstructorReferenceContext,
         FormalParameterKind,
         IdentifierContext,
         MemberKind,
         Parser,
         lengthForToken,
         lengthOfSpan,
         optional;
 import 'package:_fe_analyzer_shared/src/parser/quote.dart'
     show
         Quote,
         analyzeQuote,
         unescape,
         unescapeFirstStringPart,
         unescapeLastStringPart,
         unescapeString;
 import 'package:_fe_analyzer_shared/src/parser/stack_listener.dart'
     show FixedNullableList, GrowableList, NullValue, ParserRecovery;
 import 'package:_fe_analyzer_shared/src/parser/value_kind.dart';
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart' show Token;
 import 'package:_fe_analyzer_shared/src/scanner/token_impl.dart'
     show isBinaryOperator, isMinusOperator, isUserDefinableOperator;
 import 'package:_fe_analyzer_shared/src/util/link.dart';
 import 'package:kernel/ast.dart';
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/clone.dart';
 import 'package:kernel/core_types.dart';
 import 'package:kernel/src/bounds_checks.dart' hide calculateBounds;
 import 'package:kernel/transformations/flags.dart';
 import 'package:kernel/type_algebra.dart';
 import 'package:kernel/type_environment.dart';

 import '../builder/builder.dart';
 import '../builder/class_builder.dart';
 import '../builder/constructor_builder.dart';
 import '../builder/declaration_builder.dart';
 import '../builder/extension_builder.dart';
 import '../builder/field_builder.dart';
 import '../builder/formal_parameter_builder.dart';
 import '../builder/function_type_builder.dart';
 import '../builder/invalid_type_declaration_builder.dart';
 import '../builder/library_builder.dart';
 import '../builder/member_builder.dart';
 import '../builder/modifier_builder.dart';
 import '../builder/named_type_builder.dart';
 import '../builder/nullability_builder.dart';
 import '../builder/prefix_builder.dart';
 import '../builder/type_alias_builder.dart';
 import '../builder/type_builder.dart';
 import '../builder/type_declaration_builder.dart';
 import '../builder/type_variable_builder.dart';
 import '../builder/variable_builder.dart';
 import '../builder/void_type_declaration_builder.dart';
 import '../constant_context.dart' show ConstantContext;
 import '../dill/dill_library_builder.dart' show DillLibraryBuilder;
 import '../fasta_codes.dart' as fasta;
 import '../fasta_codes.dart'
     show
         LocatedMessage,
         Message,
         Template,
         noLength,
         templateExperimentNotEnabled;
 import '../identifiers.dart'
     show Identifier, InitializedIdentifier, QualifiedName, flattenName;
 import '../kernel/utils.dart';
 import '../messages.dart' as messages show getLocationFromUri;
 import '../modifier.dart'
     show Modifier, constMask, covariantMask, finalMask, lateMask, requiredMask;
 import '../names.dart' show emptyName, minusName, plusName;
 import '../problems.dart'
     show internalProblem, unexpected, unhandled, unsupported;
 import '../scope.dart';
 import '../source/diet_parser.dart';
 import '../source/scope_listener.dart' show JumpTargetKind, ScopeListener;
 import '../source/source_constructor_builder.dart';
 import '../source/source_enum_builder.dart';
 import '../source/source_factory_builder.dart';
 import '../source/source_field_builder.dart';
 import '../source/source_function_builder.dart';
 import '../source/source_library_builder.dart' show SourceLibraryBuilder;
 import '../source/source_procedure_builder.dart';
 import '../source/stack_listener_impl.dart' show offsetForToken;
 import '../source/value_kinds.dart';
 import '../type_inference/type_inferrer.dart'
     show TypeInferrer, InferredFunctionBody, InitializerInferenceResult;
 import '../type_inference/type_schema.dart' show UnknownType;
 import '../util/helpers.dart' show DelayedActionPerformer;
 import 'collections.dart';
 import 'constness.dart' show Constness;
 import 'constructor_tearoff_lowering.dart';
 import 'expression_generator.dart';
 import 'expression_generator_helper.dart';
 import 'forest.dart' show Forest;
 import 'implicit_type_argument.dart' show ImplicitTypeArgument;
 import 'internal_ast.dart';
 import 'kernel_variable_builder.dart';
 import 'load_library_builder.dart';
 import 'redirecting_factory_body.dart'
     show
         RedirectingFactoryBody,
         RedirectionTarget,
         getRedirectingFactoryBody,
         getRedirectionTarget;
 import 'type_algorithms.dart' show calculateBounds;
 import 'utils.dart';

 // TODO(ahe): Remove this and ensure all nodes have a location.
 const int noLocation = TreeNode.noOffset;

 // TODO(danrubel): Remove this once control flow and spread collection support
 // has been enabled by default.
 const Object invalidCollectionElement = const Object();

 class BodyBuilder extends ScopeListener<JumpTarget>
     implements ExpressionGeneratorHelper, EnsureLoaded, DelayedActionPerformer {
   @override
   final Forest forest;

   // TODO(ahe): Rename [library] to 'part'.
   @override
   final SourceLibraryBuilder libraryBuilder;

   final ModifierBuilder member;

   /// The class, mixin or extension declaration in which [member] is declared,
   /// if any.
   final DeclarationBuilder? declarationBuilder;

   /// The class or mixin declaration in which [member] is declared, if any.
   final ClassBuilder? classBuilder;

   final ClassHierarchy hierarchy;

   @override
   final CoreTypes coreTypes;

   final bool isDeclarationInstanceMember;

   final Scope enclosingScope;

   final bool enableNative;

   final bool stringExpectedAfterNative;

   /// Whether to ignore an unresolved reference to `main` within the body of
   /// `_getMainClosure` when compiling the current library.
   ///
   /// This as a temporary workaround. The standalone VM and flutter have
   /// special logic to resolve `main` in `_getMainClosure`, this flag is used to
   /// ignore that reference to `main`, but only on libraries where we expect to
   /// see it (today that is dart:_builtin and dart:ui).
   ///
   // TODO(ahe,sigmund): remove when the VM gets rid of the special rule, see
   // https://github.com/dart-lang/sdk/issues/28989.
   final bool ignoreMainInGetMainClosure;

   // TODO(ahe): Consider renaming [uri] to 'partUri'.
   @override
   final Uri uri;

   final TypeInferrer typeInferrer;

   /// Only used when [member] is a constructor. It tracks if an implicit super
   /// initializer is needed.
   ///
   /// An implicit super initializer isn't needed
   ///
   /// 1. if the current class is Object,
   /// 2. if there is an explicit super initializer,
   /// 3. if there is a redirecting (this) initializer, or
   /// 4. if a compile-time error prevented us from generating code for an
   ///    initializer. This avoids cascading errors.
   bool needsImplicitSuperInitializer;

   Scope? formalParameterScope;

   /// This is set to true when we start parsing an initializer. We use this to
   /// find the correct scope for initializers like in this example:
   ///
   ///     class C {
   ///       final x;
   ///       C(x) : x = x;
   ///     }
   ///
   /// When parsing this initializer `x = x`, `x` must be resolved in two
   /// different scopes. The first `x` must be resolved in the class' scope, the
   /// second in the formal parameter scope.
   bool inInitializerLeftHandSide = false;

   /// This is set to true when we are parsing constructor initializers.
   bool inConstructorInitializer = false;

   /// Set to `true` when we are parsing a field initializer either directly
   /// or within an initializer list.
   ///
   /// For instance in `<init>` in
   ///
   ///    var foo = <init>;
   ///    class Class {
   ///      var bar = <init>;
   ///      Class() : <init>;
   ///    }
   ///
   /// This is used to determine whether instance properties are available.
   bool inFieldInitializer = false;

   /// `true` if we are directly in a field initializer of a late field.
   ///
   /// For instance in `<init>` in
   ///
   ///    late var foo = <init>;
   ///    class Class {
   ///      late var bar = <init>;
   ///      Class() : bar = 42;
   ///    }
   ///
   bool inLateFieldInitializer = false;

   /// `true` if we are directly in the initializer of a late local.
   ///
   /// For instance in `<init>` in
   ///
   ///    method() {
   ///      late var foo = <init>;
   ///    }
   ///    class Class {
   ///      method() {
   ///        late var bar = <init>;
   ///      }
   ///    }
   ///
   bool get inLateLocalInitializer => _localInitializerState.head;

   Link<bool> _isOrAsOperatorTypeState = const Link<bool>().prepend(false);

   bool get inIsOrAsOperatorType => _isOrAsOperatorTypeState.head;

   Link<bool> _localInitializerState = const Link<bool>().prepend(false);

   List<Initializer>? _initializers;

   bool inCatchClause = false;

   bool inCatchBlock = false;

   int functionNestingLevel = 0;

   // Set when a spread element is encountered in a collection so the collection
   // needs to be desugared after type inference.
   bool transformCollections = false;

   // Set by type inference when a set literal is encountered that needs to be
   // transformed because the backend target does not support set literals.
   bool transformSetLiterals = false;

   Statement? problemInLoopOrSwitch;

   Scope? switchScope;

   late _BodyBuilderCloner _cloner = new _BodyBuilderCloner(this);

   @override
   ConstantContext constantContext = ConstantContext.none;

   DartType? currentLocalVariableType;

   // Using non-null value to initialize this field based on performance advice
   // from VM engineers. TODO(ahe): Does this still apply?
   int currentLocalVariableModifiers = -1;

   /// If non-null, records instance fields which have already been initialized
   /// and where that was.
   Map<String, int>? initializedFields;

   /// List of built redirecting factory invocations.  The targets of the
   /// invocations are to be resolved in a separate step.
   final List<FactoryConstructorInvocation> redirectingFactoryInvocations = [];

   /// List of redirecting factory invocations delayed for resolution.
   ///
   /// A resolution of a redirecting factory invocation can be delayed because
   /// the inference in the declaration of the redirecting factory isn't done
   /// yet.
   final List<FactoryConstructorInvocation>
       delayedRedirectingFactoryInvocations = [];

   /// List of built type aliased generative constructor invocations that
   /// require unaliasing.
   final List<TypeAliasedConstructorInvocation>
       typeAliasedConstructorInvocations = [];

   /// List of built type aliased factory constructor invocations that require
   /// unaliasing.
   final List<TypeAliasedFactoryInvocation> typeAliasedFactoryInvocations = [];

   /// List of type aliased factory invocations delayed for resolution.
   ///
   /// A resolution of a type aliased factory invocation can be delayed because
   /// the inference in the declaration of the target isn't done yet.
   final List<TypeAliasedFactoryInvocation>
       delayedTypeAliasedFactoryInvocations = [];

   /// Variables with metadata.  Their types need to be inferred late, for
   /// example, in [finishFunction].
   List<VariableDeclaration>? variablesWithMetadata;

   /// More than one variable declared in a single statement that has metadata.
   /// Their types need to be inferred late, for example, in [finishFunction].
   List<List<VariableDeclaration>>? multiVariablesWithMetadata;

   /// If the current member is an instance member in an extension declaration,
   /// [extensionThis] holds the synthetically add parameter holding the value
   /// for `this`.
   final VariableDeclaration? extensionThis;

   final List<TypeParameter>? extensionTypeParameters;

   BodyBuilder(
       {required this.libraryBuilder,
       required this.member,
       required this.enclosingScope,
       this.formalParameterScope,
       required this.hierarchy,
       required this.coreTypes,
       this.declarationBuilder,
       required this.isDeclarationInstanceMember,
       this.extensionThis,
       this.extensionTypeParameters,
       required this.uri,
       required this.typeInferrer})
       : forest = const Forest(),
         classBuilder =
             declarationBuilder is ClassBuilder ? declarationBuilder : null,
         enableNative = libraryBuilder.loader.target.backendTarget
             .enableNative(libraryBuilder.importUri),
         stringExpectedAfterNative = libraryBuilder
             .loader.target.backendTarget.nativeExtensionExpectsString,
         ignoreMainInGetMainClosure =
             libraryBuilder.importUri.scheme == 'dart' &&
                 (libraryBuilder.importUri.path == "_builtin" ||
                     libraryBuilder.importUri.path == "ui"),
         needsImplicitSuperInitializer = declarationBuilder is ClassBuilder &&
             coreTypes.objectClass != declarationBuilder.cls,
         super(enclosingScope) {
     formalParameterScope?.forEach((String name, Builder builder) {
       if (builder is VariableBuilder) {
         typeInferrer.assignedVariables.declare(builder.variable!);
       }
     });
   }

   BodyBuilder.withParents(FieldBuilder field, SourceLibraryBuilder part,
       DeclarationBuilder? declarationBuilder, TypeInferrer typeInferrer)
       : this(
             libraryBuilder: part,
             member: field,
             enclosingScope: declarationBuilder?.scope ?? field.library.scope,
             formalParameterScope: null,
             hierarchy: part.loader.hierarchy,
             coreTypes: part.loader.coreTypes,
             declarationBuilder: declarationBuilder,
             isDeclarationInstanceMember: field.isDeclarationInstanceMember,
             extensionThis: null,
             uri: field.fileUri!,
             typeInferrer: typeInferrer);

   BodyBuilder.forField(FieldBuilder field, TypeInferrer typeInferrer)
       : this.withParents(
             field,
             field.parent is DeclarationBuilder
                 ? field.parent!.parent as SourceLibraryBuilder
                 : field.parent as SourceLibraryBuilder,
             field.parent is DeclarationBuilder
                 ? field.parent as DeclarationBuilder
                 : null,
             typeInferrer);

   BodyBuilder.forOutlineExpression(
       SourceLibraryBuilder library,
       DeclarationBuilder? declarationBuilder,
       ModifierBuilder member,
       Scope scope,
       Uri fileUri,
       {Scope? formalParameterScope})
       : this(
             libraryBuilder: library,
             member: member,
             enclosingScope: scope,
             formalParameterScope: formalParameterScope,
             hierarchy: library.loader.hierarchy,
             coreTypes: library.loader.coreTypes,
             declarationBuilder: declarationBuilder,
             isDeclarationInstanceMember: member.isDeclarationInstanceMember,
             extensionThis: null,
             uri: fileUri,
             typeInferrer: library.loader.typeInferenceEngine
                 .createLocalTypeInferrer(
                     fileUri, declarationBuilder?.thisType, library, null));

   bool get inConstructor {
     return functionNestingLevel == 0 && member is ConstructorBuilder;
   }

   @override
   bool get isDeclarationInstanceContext {
     return isDeclarationInstanceMember || member is ConstructorBuilder;
   }

   @override
   InstanceTypeVariableAccessState get instanceTypeVariableAccessState {
     if (member.isExtensionMember && member.isField && !member.isExternal) {
       return InstanceTypeVariableAccessState.Invalid;
     } else if (isDeclarationInstanceContext || member is DeclarationBuilder) {
       return InstanceTypeVariableAccessState.Allowed;
     } else {
       return InstanceTypeVariableAccessState.Disallowed;
     }
   }

   @override
   TypeEnvironment get typeEnvironment => typeInferrer.typeSchemaEnvironment;

   DartType get implicitTypeArgument => const ImplicitTypeArgument();

   @override
   bool get enableExtensionTypesInLibrary {
     return libraryBuilder.enableExtensionTypesInLibrary;
   }

   @override
   bool get enableConstFunctionsInLibrary {
     return libraryBuilder.enableConstFunctionsInLibrary;
   }

   @override
   bool get enableConstructorTearOffsInLibrary {
     return libraryBuilder.enableConstructorTearOffsInLibrary;
   }

   @override
   bool get enableNamedArgumentsAnywhereInLibrary {
     return libraryBuilder.enableNamedArgumentsAnywhereInLibrary;
   }

   void _enterLocalState({bool inLateLocalInitializer: false}) {
     _localInitializerState =
         _localInitializerState.prepend(inLateLocalInitializer);
   }

   void _exitLocalState() {
     _localInitializerState = _localInitializerState.tail!;
   }

   @override
   void registerVariableAssignment(VariableDeclaration variable) {
     typeInferrer.assignedVariables.write(variable);
   }

   @override
   VariableDeclarationImpl createVariableDeclarationForValue(
       Expression expression) {
     VariableDeclarationImpl variable =
         forest.createVariableDeclarationForValue(expression);
     typeInferrer.assignedVariables.declare(variable);
     return variable;
   }

   @override
   void push(Object? node) {
     if (node is DartType) {
       unhandled("DartType", "push", -1, uri);
     }
     inInitializerLeftHandSide = false;
     super.push(node);
   }

   Expression popForValue() => toValue(pop());

   Expression popForEffect() => toEffect(pop());

   Expression? popForValueIfNotNull(Object? value) {
     return value == null ? null : popForValue();
   }

   @override
   Expression toValue(Object? node) {
     if (node is Generator) {
       return node.buildSimpleRead();
     } else if (node is Expression) {
       return node;
     } else if (node is SuperInitializer) {
       return buildProblem(
           fasta.messageSuperAsExpression, node.fileOffset, noLength);
     } else if (node is ProblemBuilder) {
       return buildProblem(node.message, node.charOffset, noLength);
     } else {
       return unhandled("${node.runtimeType}", "toValue", -1, uri);
     }
   }

   Expression toEffect(Object? node) {
     if (node is Generator) return node.buildForEffect();
     return toValue(node);
   }

   List<Expression> popListForValue(int n) {
     List<Expression> list =
         new List<Expression>.filled(n, dummyExpression, growable: true);
     for (int i = n - 1; i >= 0; i--) {
       list[i] = popForValue();
     }
     return list;
   }

   List<Expression> popListForEffect(int n) {
     List<Expression> list =
         new List<Expression>.filled(n, dummyExpression, growable: true);
     for (int i = n - 1; i >= 0; i--) {
       list[i] = popForEffect();
     }
     return list;
   }

   Statement popBlock(int count, Token openBrace, Token? closeBrace) {
     return forest.createBlock(
         offsetForToken(openBrace),
         offsetForToken(closeBrace),
         const GrowableList<Statement>()
                 .popNonNullable(stack, count, dummyStatement) ??
             <Statement>[]);
   }

   Statement? popStatementIfNotNull(Object? value) {
     return value == null ? null : popStatement();
   }

   Statement popStatement() => forest.wrapVariables(pop() as Statement);

   Statement? popNullableStatement() {
     Statement? statement = pop(NullValue.Block) as Statement?;
     if (statement != null) {
       statement = forest.wrapVariables(statement);
     }
     return statement;
   }

   void enterSwitchScope() {
     push(switchScope ?? NullValue.SwitchScope);
     switchScope = scope;
   }

   void exitSwitchScope() {
     Scope? outerSwitchScope = pop() as Scope?;
     if (switchScope!.unclaimedForwardDeclarations != null) {
       switchScope!.unclaimedForwardDeclarations!
           .forEach((String name, JumpTarget declaration) {
         if (outerSwitchScope == null) {
           for (Statement statement in declaration.users) {
             statement.parent!.replaceChild(
                 statement,
                 wrapInProblemStatement(statement,
                     fasta.templateLabelNotFound.withArguments(name)));
           }
         } else {
           outerSwitchScope.forwardDeclareLabel(name, declaration);
         }
       });
     }
     switchScope = outerSwitchScope;
   }

   void wrapVariableInitializerInError(
       VariableDeclaration variable,
       Template<Message Function(String name)> template,
       List<LocatedMessage> context) {
     String name = variable.name!;
     int offset = variable.fileOffset;
     Message message = template.withArguments(name);
     if (variable.initializer == null) {
       variable.initializer =
           buildProblem(message, offset, name.length, context: context)
             ..parent = variable;
     } else {
       variable.initializer = wrapInLocatedProblem(
           variable.initializer!, message.withLocation(uri, offset, name.length),
           context: context)
         ..parent = variable;
     }
   }

   void declareVariable(VariableDeclaration variable, Scope scope) {
     String name = variable.name!;
     Builder? existing = scope.lookupLocalMember(name, setter: false);
     if (existing != null) {
       // This reports an error for duplicated declarations in the same scope:
       // `{ var x; var x; }`
       wrapVariableInitializerInError(
           variable, fasta.templateDuplicatedDeclaration, <LocatedMessage>[
         fasta.templateDuplicatedDeclarationCause
             .withArguments(name)
             .withLocation(uri, existing.charOffset, name.length)
       ]);
       return;
     }
     LocatedMessage? context = scope.declare(
         variable.name!, new VariableBuilderImpl(variable, member, uri), uri);
     if (context != null) {
       // This case is different from the above error. In this case, the problem
       // is using `x` before it's declared: `{ var x; { print(x); var x;
       // }}`. In this case, we want two errors, the `x` in `print(x)` and the
       // second (or innermost declaration) of `x`.
       wrapVariableInitializerInError(
           variable,
           fasta.templateDuplicatedNamePreviouslyUsed,
           <LocatedMessage>[context]);
     }
   }

   @override
   JumpTarget createJumpTarget(JumpTargetKind kind, int charOffset) {
     return new JumpTarget(
         kind, functionNestingLevel, member as MemberBuilder, charOffset);
   }

   void inferAnnotations(TreeNode? parent, List<Expression>? annotations) {
     if (annotations != null) {
       typeInferrer.inferMetadata(this, parent, annotations);
       libraryBuilder.loader.transformListPostInference(annotations,
           transformSetLiterals, transformCollections, libraryBuilder.library);
     }
   }

   @override
   void beginMetadata(Token token) {
     debugEvent("beginMetadata");
     super.push(constantContext);
     constantContext = ConstantContext.inferred;
     assert(checkState(token, [ValueKinds.ConstantContext]));
   }

   @override
   void endMetadata(Token beginToken, Token? periodBeforeName, Token endToken) {
     assert(checkState(beginToken, [
       /*arguments*/ ValueKinds.ArgumentsOrNull,
       /*suffix*/ if (periodBeforeName != null)
         unionOfKinds([ValueKinds.Identifier, ValueKinds.ParserRecovery]),
       /*type arguments*/ ValueKinds.TypeArgumentsOrNull,
       /*type*/ unionOfKinds([
         ValueKinds.Generator,
         ValueKinds.QualifiedName,
         ValueKinds.ProblemBuilder,
         ValueKinds.ParserRecovery
       ])
     ]));
     debugEvent("Metadata");
     Arguments? arguments = pop() as Arguments?;
     pushQualifiedReference(
         beginToken.next!, periodBeforeName, ConstructorReferenceContext.Const);
     assert(checkState(beginToken, [
       /*constructor name identifier*/ ValueKinds.IdentifierOrNull,
       /*constructor name*/ ValueKinds.Name,
       /*type arguments*/ ValueKinds.TypeArgumentsOrNull,
       /*class*/ unionOfKinds([
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
         ValueKinds.ParserRecovery
       ]),
     ]));
     if (arguments != null) {
       push(arguments);
       _buildConstructorReferenceInvocation(
           beginToken.next!, beginToken.offset, Constness.explicitConst,
           inMetadata: true, inImplicitCreationContext: false);
       push(popForValue());
     } else {
       pop(); // Name last identifier
       String? name = pop() as String?;
       pop(); // Type arguments (ignored, already reported by parser).
       Object? expression = pop();
       if (expression is Identifier) {
         Identifier identifier = expression;
         expression = new UnresolvedNameGenerator(this, identifier.token,
             new Name(identifier.name, libraryBuilder.nameOrigin),
             unresolvedReadKind: UnresolvedKind.Unknown);
       }
       if (name?.isNotEmpty ?? false) {
         Token period = periodBeforeName ?? beginToken.next!.next!;
         Generator generator = expression as Generator;
         expression = generator.buildSelectorAccess(
             new PropertySelector(
                 this, period.next!, new Name(name!, libraryBuilder.nameOrigin)),
             period.next!.offset,
             false);
       }

       ConstantContext savedConstantContext = pop() as ConstantContext;
       if (expression is! StaticAccessGenerator &&
           expression is! VariableUseGenerator &&
           // TODO(johnniwinther): Stop using the type of the generator here.
           // Ask a property instead.
           (expression is! ReadOnlyAccessGenerator ||
               expression is TypeUseGenerator ||
               expression is ParenthesizedExpressionGenerator)) {
         Expression value = toValue(expression);
         push(wrapInProblem(value, fasta.messageExpressionNotMetadata,
             value.fileOffset, noLength));
       } else {
         push(toValue(expression));
       }
       constantContext = savedConstantContext;
     }
     assert(checkState(beginToken, [ValueKinds.Expression]));
   }

   @override
   void endMetadataStar(int count) {
     assert(checkState(null, repeatedKinds(ValueKinds.Expression, count)));
     debugEvent("MetadataStar");
     if (count == 0) {
       push(NullValue.Metadata);
     } else {
       push(const GrowableList<Expression>()
               .popNonNullable(stack, count, dummyExpression) ??
           NullValue.Metadata /* Ignore parser recovery */);
     }
     assert(checkState(null, [ValueKinds.AnnotationListOrNull]));
   }

   @override
   void endTopLevelFields(
       Token? externalToken,
       Token? staticToken,
       Token? covariantToken,
       Token? lateToken,
       Token? varFinalOrConst,
       int count,
       Token beginToken,
       Token endToken) {
     debugEvent("TopLevelFields");
     if (!libraryBuilder.isNonNullableByDefault) {
       reportNonNullableModifierError(lateToken);
       if (externalToken != null) {
         handleRecoverableError(
             fasta.messageExternalField, externalToken, externalToken);
       }
     }
     push(count);
     assert(checkState(beginToken, [ValueKinds.Integer]));
   }

   @override
   void endClassFields(
       Token? abstractToken,
       Token? externalToken,
       Token? staticToken,
       Token? covariantToken,
       Token? lateToken,
       Token? varFinalOrConst,
       int count,
       Token beginToken,
       Token endToken) {
     debugEvent("Fields");
     if (!libraryBuilder.isNonNullableByDefault) {
       reportNonNullableModifierError(lateToken);
       if (abstractToken != null) {
         handleRecoverableError(
             fasta.messageAbstractClassMember, abstractToken, abstractToken);
       }
       if (externalToken != null) {
         handleRecoverableError(
             fasta.messageExternalField, externalToken, externalToken);
       }
     }
     push(count);
     assert(checkState(beginToken, [ValueKinds.Integer]));
   }

   void finishFields() {
     debugEvent("finishFields");
     assert(checkState(null, [/*field count*/ ValueKinds.Integer]));
     int count = pop() as int;
     List<SourceFieldBuilder> fields = [];
     for (int i = 0; i < count; i++) {
       assert(checkState(null, [
         ValueKinds.FieldInitializerOrNull,
         ValueKinds.Identifier,
       ]));
       Expression? initializer = pop() as Expression?;
       Identifier identifier = pop() as Identifier;
       String name = identifier.name;
       Builder declaration;
       if (declarationBuilder != null) {
         declaration =
             declarationBuilder!.lookupLocalMember(name, required: true)!;
       } else {
         declaration = libraryBuilder.lookupLocalMember(name, required: true)!;
       }
       SourceFieldBuilder fieldBuilder;
       if (declaration.isField && declaration.next == null) {
         fieldBuilder = declaration as SourceFieldBuilder;
       } else {
         continue;
       }
       fields.add(fieldBuilder);
       if (initializer != null) {
         if (fieldBuilder.isDuplicate) {
           // Duplicate definition. The field might not be the correct one,
           // so we skip inference of the initializer.
           // Error reporting and recovery is handled elsewhere.
         } else if (fieldBuilder.hasBodyBeenBuilt) {
           // The initializer was already compiled (e.g., if it appear in the
           // outline, like constant field initializers) so we do not need to
           // perform type inference or transformations.

           // If the body is already built and it's a type aliased constructor or
           // factory invocation, they shouldn't be checked or resolved the
           // second time, so they are removed from the corresponding lists.
           if (initializer is TypeAliasedConstructorInvocation) {
             typeAliasedConstructorInvocations.remove(initializer);
           }
           if (initializer is TypeAliasedFactoryInvocation) {
             typeAliasedFactoryInvocations.remove(initializer);
           }
         } else {
           initializer = typeInferrer
               .inferFieldInitializer(this, fieldBuilder.builtType, initializer)
               .expression;

           if (transformCollections || transformSetLiterals) {
             // Wrap the initializer in a temporary parent expression; the
             // transformations need a parent relation.
             Not wrapper = new Not(initializer);
             libraryBuilder.loader.transformPostInference(
                 wrapper,
                 transformSetLiterals,
                 transformCollections,
                 libraryBuilder.library);
             initializer = wrapper.operand;
           }
           fieldBuilder.buildBody(coreTypes, initializer);
         }
       } else if (!fieldBuilder.hasBodyBeenBuilt) {
         fieldBuilder.buildBody(coreTypes, null);
       }
     }
     assert(checkState(
         null, [ValueKinds.TypeOrNull, ValueKinds.AnnotationListOrNull]));
     {
       // TODO(ahe): The type we compute here may be different from what is
       // computed in the outline phase. We should make sure that the outline
       // phase computes the same type. See
       // pkg/front_end/testcases/regress/issue_32200.dart for an example where
       // not calling [buildDartType] leads to a missing compile-time
       // error. Also, notice that the type of the problematic field isn't
       // `invalid-type`.
       TypeBuilder? type = pop() as TypeBuilder?;
       if (type != null) {
         buildDartType(type, allowPotentiallyConstantType: false);
       }
     }
     pop(); // Annotations.

     performBacklogComputations();
     assert(stack.length == 0);
   }

   /// Perform delayed computations that were put on back log during body
   /// building.
   ///
   /// Back logged computations include resolution of redirecting factory
   /// invocations and checking of typedef types.
   void performBacklogComputations(
       [List<DelayedActionPerformer>? delayedActionPerformers]) {
     _finishVariableMetadata();
     _unaliasTypeAliasedConstructorInvocations();
     _unaliasTypeAliasedFactoryInvocations(typeAliasedFactoryInvocations);
     _resolveRedirectingFactoryTargets(redirectingFactoryInvocations);
     libraryBuilder.checkUncheckedTypedefTypes(typeEnvironment);
     if (hasDelayedActions) {
       assert(
           delayedActionPerformers != null,
           "Body builder has delayed actions that cannot be performed: "
           "$delayedRedirectingFactoryInvocations");
       delayedActionPerformers?.add(this);
     }
   }

   void finishRedirectingFactoryBody() {
     performBacklogComputations();
   }

   @override
   void endMember() {
     debugEvent("Member");
   }

   @override
   void endBlockFunctionBody(int count, Token? openBrace, Token closeBrace) {
     debugEvent("BlockFunctionBody");
     if (openBrace == null) {
       assert(count == 0);
       push(NullValue.Block);
     } else {
       Statement block = popBlock(count, openBrace, closeBrace);
       exitLocalScope();
       push(block);
     }
     assert(checkState(closeBrace, [ValueKinds.StatementOrNull]));
   }

   void prepareInitializers() {
     SourceFunctionBuilder member = this.member as SourceFunctionBuilder;
     scope = member.computeFormalParameterInitializerScope(scope);
     if (member is DeclaredSourceConstructorBuilder) {
       member.prepareInitializers();
       if (member.formals != null) {
         for (FormalParameterBuilder formal in member.formals!) {
           if (formal.isInitializingFormal) {
             List<Initializer> initializers;
             if (member.isExternal) {
               initializers = <Initializer>[
                 buildInvalidInitializer(
                     buildProblem(
                         fasta.messageExternalConstructorWithFieldInitializers,
                         formal.charOffset,
                         formal.name.length),
                     formal.charOffset)
               ];
             } else {
               initializers = buildFieldInitializer(
                   formal.name,
                   formal.charOffset,
                   formal.charOffset,
                   new VariableGet(formal.variable!),
                   formal: formal);
             }
             for (Initializer initializer in initializers) {
               member.addInitializer(initializer, this, inferenceResult: null);
             }
           }
         }
       }
     }
   }

   @override
   void handleNoInitializers() {
     debugEvent("NoInitializers");
     if (functionNestingLevel == 0) {
       prepareInitializers();
       scope = formalParameterScope ?? new Scope.immutable();
     }
   }

   @override
   void beginInitializers(Token token) {
     debugEvent("beginInitializers");
     if (functionNestingLevel == 0) {
       prepareInitializers();
     }
     inConstructorInitializer = true;
   }

   @override
   void endInitializers(int count, Token beginToken, Token endToken) {
     debugEvent("Initializers");
     if (functionNestingLevel == 0) {
       scope = formalParameterScope ?? new Scope.immutable();
     }
     inConstructorInitializer = false;
   }

   @override
   void beginInitializer(Token token) {
     debugEvent("beginInitializer");
     inInitializerLeftHandSide = true;
     inFieldInitializer = true;
   }

   @override
   void endInitializer(Token token) {
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Initializer,
         ValueKinds.Generator,
         ValueKinds.Expression,
       ])
     ]));

     debugEvent("endInitializer");
     inFieldInitializer = false;
     assert(!inInitializerLeftHandSide);
     Object? node = pop();
     List<Initializer> initializers;

     final ModifierBuilder member = this.member;
     if (!(member is ConstructorBuilder && !member.isExternal)) {
       // An error has been reported by the parser.
       initializers = <Initializer>[];
     } else if (node is Initializer) {
       initializers = <Initializer>[node];
     } else if (node is Generator) {
       initializers = node.buildFieldInitializer(initializedFields);
     } else if (node is ConstructorInvocation) {
       initializers = <Initializer>[
         buildSuperInitializer(
             false, node.target, node.arguments, token.charOffset)
       ];
     } else {
       Expression value = toValue(node);
       if (!forest.isThrow(node)) {
         value = wrapInProblem(value, fasta.messageExpectedAnInitializer,
             value.fileOffset, noLength);
       }
       initializers = <Initializer>[
         // TODO(johnniwinther): This should probably be [value] instead of
         //  [node].
         buildInvalidInitializer(node as Expression, token.charOffset)
       ];
     }

     _initializers ??= <Initializer>[];
     _initializers!.addAll(initializers);
   }

   DartType _computeReturnTypeContext(MemberBuilder member) {
     if (member is SourceProcedureBuilder) {
       final bool isReturnTypeUndeclared = member.returnType == null &&
           member.function.returnType is DynamicType;
       return isReturnTypeUndeclared && libraryBuilder.isNonNullableByDefault
           ? const UnknownType()
           : member.function.returnType;
     } else if (member is SourceFactoryBuilder) {
       return member.function.returnType;
     } else {
       assert(member is ConstructorBuilder);
       return const DynamicType();
     }
   }

   void finishFunction(
       FormalParameters? formals, AsyncMarker asyncModifier, Statement? body) {
     debugEvent("finishFunction");
     typeInferrer.assignedVariables.finish();

     final SourceFunctionBuilder builder = member as SourceFunctionBuilder;
     if (extensionThis != null) {
       typeInferrer.flowAnalysis.declare(extensionThis!, true);
     }
     if (formals?.parameters != null) {
       for (int i = 0; i < formals!.parameters!.length; i++) {
         FormalParameterBuilder parameter = formals.parameters![i];
         typeInferrer.flowAnalysis.declare(parameter.variable!, true);
       }
       for (int i = 0; i < formals.parameters!.length; i++) {
         FormalParameterBuilder parameter = formals.parameters![i];
         Expression? initializer = parameter.variable!.initializer;
         if (!parameter.isSuperInitializingFormal &&
             (parameter.isOptional || initializer != null)) {
           if (!parameter.initializerWasInferred) {
             parameter.initializerWasInferred = true;
             if (parameter.isOptional) {
               initializer ??= forest.createNullLiteral(
                   // TODO(ahe): Should store: originParameter.fileOffset
                   // https://github.com/dart-lang/sdk/issues/32289
                   noLocation);
             }
             VariableDeclaration originParameter = builder.getFormalParameter(i);
             initializer = typeInferrer.inferParameterInitializer(
                 this,
                 initializer!,
                 originParameter.type,
                 parameter.hasDeclaredInitializer);
             originParameter.initializer = initializer..parent = originParameter;
             libraryBuilder.loader.transformPostInference(
                 originParameter,
                 transformSetLiterals,
                 transformCollections,
                 libraryBuilder.library);
           }

           VariableDeclaration? tearOffParameter =
               builder.getTearOffParameter(i);
           if (tearOffParameter != null) {
             Expression tearOffInitializer =
                 _cloner.cloneInContext(initializer!);
             tearOffParameter.initializer = tearOffInitializer
               ..parent = tearOffParameter;
             libraryBuilder.loader.transformPostInference(
                 tearOffParameter,
                 transformSetLiterals,
                 transformCollections,
                 libraryBuilder.library);
           }
         }
       }
     }
     if (builder is DeclaredSourceConstructorBuilder) {
       finishConstructor(builder, asyncModifier, body);
     } else if (builder is SourceProcedureBuilder) {
       builder.asyncModifier = asyncModifier;
     } else if (builder is SourceFactoryBuilder) {
       builder.asyncModifier = asyncModifier;
     } else {
       unhandled("${builder.runtimeType}", "finishFunction", builder.charOffset,
           builder.fileUri);
     }

     InferredFunctionBody? inferredFunctionBody;
     if (body != null) {
       inferredFunctionBody = typeInferrer.inferFunctionBody(
           this,
           builder.charOffset,
           _computeReturnTypeContext(builder),
           asyncModifier,
           body);
       body = inferredFunctionBody.body;
       builder.function.futureValueType = inferredFunctionBody.futureValueType;
       libraryBuilder.loader.transformPostInference(body, transformSetLiterals,
           transformCollections, libraryBuilder.library);
     }

     if (builder.returnType != null) {
       checkAsyncReturnType(asyncModifier, builder.function.returnType,
           builder.charOffset, builder.name.length);
     }

     if (builder.kind == ProcedureKind.Setter) {
       if (formals?.parameters == null ||
           formals!.parameters!.length != 1 ||
           formals.parameters!.single.isOptional) {
         int charOffset = formals?.charOffset ??
             body?.fileOffset ??
             builder.member.fileOffset;
         if (body == null) {
           body = new EmptyStatement()..fileOffset = charOffset;
         }
         if (builder.formals != null) {
           // Illegal parameters were removed by the function builder.
           // Add them as local variable to put them in scope of the body.
           List<Statement> statements = <Statement>[];
           for (FormalParameterBuilder parameter in builder.formals!) {
             statements.add(parameter.variable!);
           }
           statements.add(body);
           body = forest.createBlock(charOffset, noLocation, statements);
         }
         body = forest.createBlock(charOffset, noLocation, <Statement>[
           forest.createExpressionStatement(
               noLocation,
               // This error is added after type inference is done, so we
               // don't need to wrap errors in SyntheticExpressionJudgment.
               buildProblem(fasta.messageSetterWithWrongNumberOfFormals,
                   charOffset, noLength)),
           body,
         ]);
       }
     }
     // No-such-method forwarders get their bodies injected during outline
     // building, so we should skip them here.
     bool isNoSuchMethodForwarder = (builder.function.parent is Procedure &&
         (builder.function.parent as Procedure).isNoSuchMethodForwarder);
     if (body != null) {
       if (!builder.isExternal && !isNoSuchMethodForwarder) {
         builder.body = body;
       } else {
         builder.body = new Block(<Statement>[
           new ExpressionStatement(buildProblem(
               fasta.messageExternalMethodWithBody, body.fileOffset, noLength))
             ..fileOffset = body.fileOffset,
           body,
         ])
           ..fileOffset = body.fileOffset;
       }
     }

     performBacklogComputations();
   }

   void checkAsyncReturnType(AsyncMarker asyncModifier, DartType returnType,
       int charOffset, int length) {
     // For async, async*, and sync* functions with declared return types, we
     // need to determine whether those types are valid.
     // We use the same trick in each case below. For example to decide whether
     // Future<T> <: [returnType] for every T, we rely on Future<Bot> and
     // transitivity of the subtyping relation because Future<Bot> <: Future<T>
     // for every T.

     // We use [problem == null] to signal success.
     Message? problem;
     switch (asyncModifier) {
       case AsyncMarker.Async:
         DartType futureBottomType = libraryBuilder.loader.futureOfBottom;
         if (!typeEnvironment.isSubtypeOf(
             futureBottomType, returnType, SubtypeCheckMode.withNullabilities)) {
           problem = fasta.messageIllegalAsyncReturnType;
         }
         break;

       case AsyncMarker.AsyncStar:
         DartType streamBottomType = libraryBuilder.loader.streamOfBottom;
         if (returnType is VoidType) {
           problem = fasta.messageIllegalAsyncGeneratorVoidReturnType;
         } else if (!typeEnvironment.isSubtypeOf(
             streamBottomType, returnType, SubtypeCheckMode.withNullabilities)) {
           problem = fasta.messageIllegalAsyncGeneratorReturnType;
         }
         break;

       case AsyncMarker.SyncStar:
         DartType iterableBottomType = libraryBuilder.loader.iterableOfBottom;
         if (returnType is VoidType) {
           problem = fasta.messageIllegalSyncGeneratorVoidReturnType;
         } else if (!typeEnvironment.isSubtypeOf(iterableBottomType, returnType,
             SubtypeCheckMode.withNullabilities)) {
           problem = fasta.messageIllegalSyncGeneratorReturnType;
         }
         break;

       case AsyncMarker.Sync:
         break; // skip
       case AsyncMarker.SyncYielding:
         unexpected("async, async*, sync, or sync*", "$asyncModifier",
             member.charOffset, uri);
     }

     if (problem != null) {
       // TODO(hillerstrom): once types get annotated with location
       // information, we can improve the quality of the error message by
       // using the offset of [returnType] (and the length of its name).
       addProblem(problem, charOffset, length);
     }
   }

   /// Ensure that the containing library of the [member] has been loaded.
   ///
   /// This is for instance important for lazy dill library builders where this
   /// method has to be called to ensure that
   /// a) The library has been fully loaded (and for instance any internal
   ///    transformation needed has been performed); and
   /// b) The library is correctly marked as being used to allow for proper
   ///    'dependency pruning'.
   @override
   void ensureLoaded(Member? member) {
     if (member == null) return;
     Library ensureLibraryLoaded = member.enclosingLibrary;
     LibraryBuilder? builder = libraryBuilder.loader
             .lookupLibraryBuilder(ensureLibraryLoaded.importUri) ??
         libraryBuilder.loader.target.dillTarget.loader
             .lookupLibraryBuilder(ensureLibraryLoaded.importUri);
     if (builder is DillLibraryBuilder) {
       builder.ensureLoaded();
     }
   }

   /// Check if the containing library of the [member] has been loaded.
   ///
   /// This is designed for use with asserts.
   /// See [ensureLoaded] for a description of what 'loaded' means and the ideas
   /// behind that.
   @override
   bool isLoaded(Member? member) {
     if (member == null) return true;
     Library ensureLibraryLoaded = member.enclosingLibrary;
     LibraryBuilder? builder = libraryBuilder.loader
             .lookupLibraryBuilder(ensureLibraryLoaded.importUri) ??
         libraryBuilder.loader.target.dillTarget.loader
             .lookupLibraryBuilder(ensureLibraryLoaded.importUri);
     if (builder is DillLibraryBuilder) {
       return builder.isBuiltAndMarked;
     }
     return true;
   }

   /// Return an [Expression] resolving the argument invocation.
   ///
   /// The arguments specify the [StaticInvocation] whose `.target` is
   /// [target], `.arguments` is [arguments], `.fileOffset` is [fileOffset],
   /// and `.isConst` is [isConst].
   /// Returns null if the invocation can't be resolved.
   Expression? _resolveRedirectingFactoryTarget(
       Procedure target, Arguments arguments, int fileOffset, bool isConst) {
     Procedure initialTarget = target;
     Expression replacementNode;

     RedirectionTarget redirectionTarget =
         getRedirectionTarget(initialTarget, this);
     Member resolvedTarget = redirectionTarget.target;
     if (redirectionTarget.typeArguments.any((type) => type is UnknownType)) {
       return null;
     }

     RedirectingFactoryBody? redirectingFactoryBody =
         getRedirectingFactoryBody(resolvedTarget);
     if (redirectingFactoryBody != null) {
       // If the redirection target is itself a redirecting factory, it means
       // that it is unresolved.
       assert(redirectingFactoryBody.isError);
       String errorMessage = redirectingFactoryBody.errorMessage!;
       replacementNode = new InvalidExpression(errorMessage)
         ..fileOffset = fileOffset;
     } else {
       Substitution substitution = Substitution.fromPairs(
           initialTarget.function.typeParameters, arguments.types);
       for (int i = 0; i < redirectionTarget.typeArguments.length; i++) {
         DartType typeArgument =
             substitution.substituteType(redirectionTarget.typeArguments[i]);
         if (i < arguments.types.length) {
           arguments.types[i] = typeArgument;
         } else {
           arguments.types.add(typeArgument);
         }
       }
       arguments.types.length = redirectionTarget.typeArguments.length;

       replacementNode = buildStaticInvocation(
           resolvedTarget,
           forest.createArguments(noLocation, arguments.positional,
               types: arguments.types,
               named: arguments.named,
               hasExplicitTypeArguments: hasExplicitTypeArguments(arguments)),
           constness: isConst ? Constness.explicitConst : Constness.explicitNew,
           charOffset: fileOffset);
     }
     return replacementNode;
   }

   void _resolveRedirectingFactoryTargets(
       List<FactoryConstructorInvocation> redirectingFactoryInvocations) {
     List<FactoryConstructorInvocation> invocations =
         redirectingFactoryInvocations.toList();
     redirectingFactoryInvocations.clear();
     for (FactoryConstructorInvocation invocation in invocations) {
       // If the invocation was invalid, it or its parent has already been
       // desugared into an exception throwing expression.  There is nothing to
       // resolve anymore.  Note that in the case where the invocation's parent
       // was invalid, type inference won't reach the invocation node and won't
       // set its inferredType field.  If type inference is disabled, reach to
       // the outermost parent to check if the node is a dead code.
       if (invocation.parent == null) continue;
       // ignore: unnecessary_null_comparison
       if (typeInferrer != null) {
         if (!invocation.hasBeenInferred) {
           continue;
         }
       } else {
         TreeNode? parent = invocation.parent;
         while (parent is! Component && parent != null) {
           parent = parent.parent;
         }
         if (parent == null) continue;
       }
       Expression? replacement = _resolveRedirectingFactoryTarget(
           invocation.target,
           invocation.arguments,
           invocation.fileOffset,
           invocation.isConst);
       if (replacement == null) {
         delayedRedirectingFactoryInvocations.add(invocation);
       } else {
         invocation.replaceWith(replacement);
       }
     }
   }

   void _unaliasTypeAliasedConstructorInvocations() {
     for (TypeAliasedConstructorInvocation invocation
         in typeAliasedConstructorInvocations) {
       bool inferred = !hasExplicitTypeArguments(invocation.arguments);
       DartType aliasedType = new TypedefType(
           invocation.typeAliasBuilder.typedef,
           Nullability.nonNullable,
           invocation.arguments.types);
       libraryBuilder.checkBoundsInType(
           aliasedType, typeEnvironment, uri, invocation.fileOffset,
           allowSuperBounded: false, inferred: inferred);
       DartType unaliasedType = aliasedType.unalias;
       List<DartType>? invocationTypeArguments = null;
       if (unaliasedType is InterfaceType) {
         invocationTypeArguments = unaliasedType.typeArguments;
       }
       Arguments invocationArguments = forest.createArguments(
           noLocation, invocation.arguments.positional,
           types: invocationTypeArguments, named: invocation.arguments.named);
       invocation.replaceWith(new ConstructorInvocation(
           invocation.target, invocationArguments,
           isConst: invocation.isConst));
     }
     typeAliasedConstructorInvocations.clear();
   }

   void _unaliasTypeAliasedFactoryInvocations(
       List<TypeAliasedFactoryInvocation> typeAliasedFactoryInvocations) {
     List<TypeAliasedFactoryInvocation> invocations =
         typeAliasedFactoryInvocations.toList();
     typeAliasedFactoryInvocations.clear();
     for (TypeAliasedFactoryInvocation invocation in invocations) {
       bool inferred = !hasExplicitTypeArguments(invocation.arguments);
       DartType aliasedType = new TypedefType(
           invocation.typeAliasBuilder.typedef,
           Nullability.nonNullable,
           invocation.arguments.types);
       libraryBuilder.checkBoundsInType(
           aliasedType, typeEnvironment, uri, invocation.fileOffset,
           allowSuperBounded: false, inferred: inferred);
       DartType unaliasedType = aliasedType.unalias;
       List<DartType>? invocationTypeArguments = null;
       if (unaliasedType is InterfaceType) {
         invocationTypeArguments = unaliasedType.typeArguments;
       }
       Arguments invocationArguments = forest.createArguments(
           noLocation, invocation.arguments.positional,
           types: invocationTypeArguments,
           named: invocation.arguments.named,
           hasExplicitTypeArguments:
               hasExplicitTypeArguments(invocation.arguments));
       Expression? replacement = _resolveRedirectingFactoryTarget(
           invocation.target,
           invocationArguments,
           invocation.fileOffset,
           invocation.isConst);
       if (replacement == null) {
         delayedTypeAliasedFactoryInvocations.add(invocation);
       } else {
         invocation.replaceWith(replacement);
       }
     }
     typeAliasedFactoryInvocations.clear();
   }

   /// Perform actions that were delayed
   ///
   /// An action can be delayed, for instance, because it depends on some
   /// calculations in another library.  For example, a resolution of a
   /// redirecting factory invocation depends on the type inference in the
   /// redirecting factory.
   @override
   void performDelayedActions() {
     if (delayedRedirectingFactoryInvocations.isNotEmpty) {
       _resolveRedirectingFactoryTargets(delayedRedirectingFactoryInvocations);
       if (delayedRedirectingFactoryInvocations.isNotEmpty) {
         for (StaticInvocation invocation
             in delayedRedirectingFactoryInvocations) {
           internalProblem(
               fasta.templateInternalProblemUnhandled.withArguments(
                   invocation.target.name.text, 'performDelayedActions'),
               invocation.fileOffset,
               uri);
         }
       }
     }
     if (delayedTypeAliasedFactoryInvocations.isNotEmpty) {
       _unaliasTypeAliasedFactoryInvocations(
           delayedTypeAliasedFactoryInvocations);
       if (delayedTypeAliasedFactoryInvocations.isNotEmpty) {
         for (StaticInvocation invocation
             in delayedTypeAliasedFactoryInvocations) {
           internalProblem(
               fasta.templateInternalProblemUnhandled.withArguments(
                   invocation.target.name.text, 'performDelayedActions'),
               invocation.fileOffset,
               uri);
         }
       }
     }
   }

   @override
   bool get hasDelayedActions {
     return delayedRedirectingFactoryInvocations.isNotEmpty ||
         delayedTypeAliasedFactoryInvocations.isNotEmpty;
   }

   void _finishVariableMetadata() {
     List<VariableDeclaration>? variablesWithMetadata =
         this.variablesWithMetadata;
     this.variablesWithMetadata = null;
     List<List<VariableDeclaration>>? multiVariablesWithMetadata =
         this.multiVariablesWithMetadata;
     this.multiVariablesWithMetadata = null;

     if (variablesWithMetadata != null) {
       for (int i = 0; i < variablesWithMetadata.length; i++) {
         inferAnnotations(
             variablesWithMetadata[i], variablesWithMetadata[i].annotations);
       }
     }
     if (multiVariablesWithMetadata != null) {
       for (int i = 0; i < multiVariablesWithMetadata.length; i++) {
         List<VariableDeclaration> variables = multiVariablesWithMetadata[i];
         List<Expression> annotations = variables.first.annotations;
         inferAnnotations(variables.first, annotations);
         for (int i = 1; i < variables.length; i++) {
           VariableDeclaration variable = variables[i];
           for (int i = 0; i < annotations.length; i++) {
             variable.addAnnotation(_cloner.cloneInContext(annotations[i]));
           }
         }
       }
     }
   }

   @override
   List<Expression> finishMetadata(Annotatable? parent) {
     assert(checkState(null, [ValueKinds.AnnotationList]));
     List<Expression> expressions = pop() as List<Expression>;
     inferAnnotations(parent, expressions);

     // The invocation of [resolveRedirectingFactoryTargets] below may change the
     // root nodes of the annotation expressions.  We need to have a parent of
     // the annotation nodes before the resolution is performed, to collect and
     // return them later.  If [parent] is not provided, [temporaryParent] is
     // used.
     ListLiteral? temporaryParent;

     if (parent != null) {
       for (Expression expression in expressions) {
         parent.addAnnotation(expression);
       }
     } else {
       temporaryParent = new ListLiteral(expressions);
     }
     performBacklogComputations();
     return temporaryParent != null ? temporaryParent.expressions : expressions;
   }

   @override
   Expression parseSingleExpression(
       Parser parser, Token token, FunctionNode parameters) {
     assert(redirectingFactoryInvocations.isEmpty);
     int fileOffset = offsetForToken(token);
     List<TypeVariableBuilder>? typeParameterBuilders;
     for (TypeParameter typeParameter in parameters.typeParameters) {
       typeParameterBuilders ??= <TypeVariableBuilder>[];
       typeParameterBuilders.add(
           new TypeVariableBuilder.fromKernel(typeParameter, libraryBuilder));
     }
     enterFunctionTypeScope(typeParameterBuilders);

     List<FormalParameterBuilder>? formals =
         parameters.positionalParameters.length == 0
             ? null
             : new List<FormalParameterBuilder>.generate(
                 parameters.positionalParameters.length, (int i) {
                 VariableDeclaration formal = parameters.positionalParameters[i];
                 return new FormalParameterBuilder(null, 0, null, formal.name!,
                     libraryBuilder, formal.fileOffset,
                     fileUri: uri)
                   ..variable = formal;
               }, growable: false);
     enterLocalScope(
         'formalParameters',
         new FormalParameters(formals, fileOffset, noLength, uri)
             .computeFormalParameterScope(scope, member, this));

     Token endToken =
         parser.parseExpression(parser.syntheticPreviousToken(token));

     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
       ])
     ]));
     Expression expression = popForValue();
     Token eof = endToken.next!;

     if (!eof.isEof) {
       expression = wrapInLocatedProblem(
           expression,
           fasta.messageExpectedOneExpression
               .withLocation(uri, eof.charOffset, eof.length));
     }

     ReturnStatementImpl fakeReturn = new ReturnStatementImpl(true, expression);
     if (formals != null) {
       for (int i = 0; i < formals.length; i++) {
         typeInferrer.flowAnalysis.declare(formals[i].variable!, true);
       }
     }
     InferredFunctionBody inferredFunctionBody = typeInferrer.inferFunctionBody(
         this, fileOffset, const DynamicType(), AsyncMarker.Sync, fakeReturn);
     assert(
         fakeReturn == inferredFunctionBody.body,
         "Previously implicit assumption about inferFunctionBody "
         "not returning anything different.");

     performBacklogComputations();
     libraryBuilder.loader.transformPostInference(fakeReturn,
         transformSetLiterals, transformCollections, libraryBuilder.library);

     return fakeReturn.expression!;
   }

   void parseInitializers(Token token, {bool doFinishConstructor = true}) {
     Parser parser = new Parser(this,
         useImplicitCreationExpression: useImplicitCreationExpressionInCfe);
     if (!token.isEof) {
       token = parser.parseInitializers(token);
       checkEmpty(token.charOffset);
     } else {
       handleNoInitializers();
     }
     if (doFinishConstructor) {
       finishConstructor(
           member as DeclaredSourceConstructorBuilder, AsyncMarker.Sync, null);
     }
   }

   Expression parseFieldInitializer(Token token) {
     Parser parser = new Parser(this,
         useImplicitCreationExpression: useImplicitCreationExpressionInCfe);
     Token endToken =
         parser.parseExpression(parser.syntheticPreviousToken(token));
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ])
     ]));
     Expression expression = popForValue();
     checkEmpty(endToken.charOffset);
     return expression;
   }

   Expression parseAnnotation(Token token) {
     Parser parser = new Parser(this,
         useImplicitCreationExpression: useImplicitCreationExpressionInCfe);
     Token endToken = parser.parseMetadata(parser.syntheticPreviousToken(token));
     assert(checkState(token, [ValueKinds.Expression]));
     Expression annotation = pop() as Expression;
     checkEmpty(endToken.charOffset);
     return annotation;
   }

   Arguments parseArguments(Token token) {
     Parser parser = new Parser(this,
         useImplicitCreationExpression: useImplicitCreationExpressionInCfe);
     token = parser.parseArgumentsRest(token);
     Arguments arguments = pop() as Arguments;
     checkEmpty(token.charOffset);
     return arguments;
   }

   void finishConstructor(DeclaredSourceConstructorBuilder builder,
       AsyncMarker asyncModifier, Statement? body) {
     /// Quotes below are from [Dart Programming Language Specification, 4th
     /// Edition](
     /// https://ecma-international.org/publications/files/ECMA-ST/ECMA-408.pdf).
     assert(builder == member);
     Constructor constructor = builder.actualConstructor;
     List<FormalParameterBuilder>? formals = builder.formals;
     if (formals != null) {
       for (int i = 0; i < formals.length; i++) {
         FormalParameterBuilder parameter = formals[i];
         typeInferrer.flowAnalysis.declare(parameter.variable!, true);
       }
     }

     List<Expression>? positionalSuperParametersAsArguments;
     List<NamedExpression>? namedSuperParametersAsArguments;
     if (formals != null) {
       for (FormalParameterBuilder formal in formals) {
         if (formal.isSuperInitializingFormal) {
           if (formal.isNamed) {
             (namedSuperParametersAsArguments ??= <NamedExpression>[]).add(
                 new NamedExpression(
                     formal.name,
                     new VariableGetImpl(formal.variable!,
                         forNullGuardedAccess: false)
                       ..fileOffset = formal.charOffset)
                   ..fileOffset = formal.charOffset);
           } else {
             (positionalSuperParametersAsArguments ??= <Expression>[]).add(
                 new VariableGetImpl(formal.variable!,
                     forNullGuardedAccess: false)
                   ..fileOffset = formal.charOffset);
           }
         }
       }
     }

     List<Initializer>? initializers = _initializers;
     if (initializers != null) {
       if (libraryBuilder.enableSuperParametersInLibrary) {
         if (initializers.isNotEmpty && initializers.last is SuperInitializer) {
           SuperInitializer superInitializer =
               initializers.last as SuperInitializer;
           Arguments arguments = superInitializer.arguments;

           if (positionalSuperParametersAsArguments != null) {
             if (arguments.positional.isNotEmpty) {
               addProblem(fasta.messagePositionalSuperParametersAndArguments,
                   arguments.fileOffset, noLength,
                   context: <LocatedMessage>[
                     fasta.messageSuperInitializerParameter.withLocation(
                         uri,
                         (positionalSuperParametersAsArguments.first
                                 as VariableGet)
                             .variable
                             .fileOffset,
                         noLength)
                   ]);
             } else {
               arguments.positional.addAll(positionalSuperParametersAsArguments);
               setParents(positionalSuperParametersAsArguments, arguments);
             }
           }
           if (namedSuperParametersAsArguments != null) {
             // TODO(cstefantsova): Report name conflicts.
             arguments.named.addAll(namedSuperParametersAsArguments);
             setParents(namedSuperParametersAsArguments, arguments);
           }

           LocatedMessage? message = checkArgumentsForFunction(
               superInitializer.target.function,
               arguments,
               arguments.fileOffset, <TypeParameter>[]);
           if (message != null) {
             initializers[initializers.length - 1] = buildInvalidInitializer(
                 buildUnresolvedError(
                     forest.createNullLiteral(superInitializer.fileOffset),
                     constructorNameForDiagnostics(
                         superInitializer.target.name.text),
                     arguments,
                     superInitializer.fileOffset,
                     isSuper: true,
                     message: message,
                     kind: UnresolvedKind.Constructor));
           }
         }
       }

       Map<Initializer, InitializerInferenceResult> inferenceResults =
           <Initializer, InitializerInferenceResult>{};
       for (Initializer initializer in initializers) {
         inferenceResults[initializer] =
             typeInferrer.inferInitializer(this, initializer);
       }
       if (!builder.isExternal) {
         for (Initializer initializer in initializers) {
           builder.addInitializer(initializer, this,
               inferenceResult: inferenceResults[initializer]!);
         }
       }
     }
     if (asyncModifier != AsyncMarker.Sync) {
       constructor.initializers.add(buildInvalidInitializer(buildProblem(
           fasta.messageConstructorNotSync, body!.fileOffset, noLength)));
     }
     if (libraryBuilder.enableEnhancedEnumsInLibrary &&
         classBuilder is SourceEnumBuilder &&
         constructor.initializers.isNotEmpty &&
         constructor.initializers.last is RedirectingInitializer) {
       RedirectingInitializer redirectingInitializer =
           constructor.initializers.last as RedirectingInitializer;
       redirectingInitializer.arguments.positional.insertAll(0, [
         new VariableGet(constructor.function.positionalParameters[0])
           ..parent = redirectingInitializer.arguments,
         new VariableGet(constructor.function.positionalParameters[1])
           ..parent = redirectingInitializer.arguments
       ]);

       LocatedMessage? message = checkArgumentsForFunction(
           redirectingInitializer.target.function,
           redirectingInitializer.arguments,
           builder.charOffset, const <TypeParameter>[]);
       if (message != null) {
         Initializer invalidInitializer = buildInvalidInitializer(
             buildUnresolvedError(
                 forest.createNullLiteral(redirectingInitializer.fileOffset),
                 constructorNameForDiagnostics(builder.name, isSuper: false),
                 redirectingInitializer.arguments,
                 redirectingInitializer.fileOffset,
                 isSuper: false,
                 message: message,
                 kind: UnresolvedKind.Constructor));
         constructor.initializers.removeLast();
         constructor.initializers.add(invalidInitializer..parent = constructor);
       }
     }
     if (needsImplicitSuperInitializer) {
       /// >If no superinitializer is provided, an implicit superinitializer
       /// >of the form super() is added at the end of k’s initializer list,
       /// >unless the enclosing class is class Object.
       Constructor? superTarget = lookupConstructor(emptyName, isSuper: true);
       Initializer initializer;
       Arguments arguments;
       List<Expression>? positionalArguments;
       List<NamedExpression>? namedArguments;
       if (libraryBuilder.enableSuperParametersInLibrary) {
         positionalArguments = positionalSuperParametersAsArguments;
         namedArguments = namedSuperParametersAsArguments;
       }
       if (classBuilder is SourceEnumBuilder) {
         assert(constructor.function.positionalParameters.length >= 2 &&
             constructor.function.positionalParameters[0].name == "index" &&
             constructor.function.positionalParameters[1].name == "name");
         (positionalArguments ??= <Expression>[]).insertAll(0, [
           new VariableGet(constructor.function.positionalParameters[0]),
           new VariableGet(constructor.function.positionalParameters[1])
         ]);
       }
       if (positionalArguments != null || namedArguments != null) {
         arguments = forest.createArguments(
             noLocation, positionalArguments ?? <Expression>[],
             named: namedArguments);
       } else {
         arguments = forest.createArgumentsEmpty(noLocation);
       }
       if (superTarget == null ||
           checkArgumentsForFunction(superTarget.function, arguments,
                   builder.charOffset, const <TypeParameter>[]) !=
               null) {
         String superclass = classBuilder!.supertypeBuilder!.fullNameForErrors;
         int length = constructor.name.text.length;
         if (length == 0) {
           length = (constructor.parent as Class).name.length;
         }
         initializer = buildInvalidInitializer(
             buildProblem(
                 fasta.templateSuperclassHasNoDefaultConstructor
                     .withArguments(superclass),
                 builder.charOffset,
                 length),
             builder.charOffset);
       } else {
         initializer = buildSuperInitializer(
             true, superTarget, arguments, builder.charOffset);
       }
       constructor.initializers.add(initializer);
     }
     setParents(constructor.initializers, constructor);
     libraryBuilder.loader.transformListPostInference(constructor.initializers,
         transformSetLiterals, transformCollections, libraryBuilder.library);
     if (body == null) {
       /// >If a generative constructor c is not a redirecting constructor
       /// >and no body is provided, then c implicitly has an empty body {}.
       /// We use an empty statement instead.
       constructor.function.body = new EmptyStatement()
         ..parent = constructor.function;
     }
   }

   @override
   void handleExpressionStatement(Token token) {
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
     ]));
     debugEvent("ExpressionStatement");
     push(forest.createExpressionStatement(
         offsetForToken(token), popForEffect()));
   }

   @override
   void endArguments(int count, Token beginToken, Token endToken) {
     debugEvent("Arguments");
     List<Object?>? arguments = count == 0
         ? <Object>[]
         : const FixedNullableList<Object>().pop(stack, count);
     if (arguments == null) {
       push(new ParserRecovery(beginToken.charOffset));
       return;
     }
     List<Object?>? argumentsOriginalOrder;
     if (libraryBuilder.enableNamedArgumentsAnywhereInLibrary) {
       argumentsOriginalOrder = new List<Object?>.from(arguments);
     }
     int firstNamedArgumentIndex = arguments.length;
     int positionalCount = 0;
     bool hasNamedBeforePositional = false;
     for (int i = 0; i < arguments.length; i++) {
       Object? node = arguments[i];
       if (node is NamedExpression) {
         firstNamedArgumentIndex =
             i < firstNamedArgumentIndex ? i : firstNamedArgumentIndex;
       } else {
         positionalCount++;
         Expression argument = toValue(node);
         arguments[i] = argument;
         argumentsOriginalOrder?[i] = argument;
         if (i > firstNamedArgumentIndex) {
           hasNamedBeforePositional = true;
           if (!libraryBuilder.enableNamedArgumentsAnywhereInLibrary) {
             arguments[i] = new NamedExpression(
                 "#$i",
                 buildProblem(fasta.messageExpectedNamedArgument,
                     argument.fileOffset, noLength))
               ..fileOffset = beginToken.charOffset;
           }
         }
       }
     }
     if (!hasNamedBeforePositional) {
       argumentsOriginalOrder = null;
     }
     if (firstNamedArgumentIndex < arguments.length) {
       List<Expression> positional;
       List<NamedExpression> named;
       if (libraryBuilder.enableNamedArgumentsAnywhereInLibrary) {
         positional =
             new List<Expression>.filled(positionalCount, dummyExpression);
         named = new List<NamedExpression>.filled(
             arguments.length - positionalCount, dummyNamedExpression);
         int positionalIndex = 0;
         int namedIndex = 0;
         for (int i = 0; i < arguments.length; i++) {
           if (arguments[i] is NamedExpression) {
             named[namedIndex++] = arguments[i] as NamedExpression;
           } else {
             positional[positionalIndex++] = arguments[i] as Expression;
           }
         }
         assert(
             positionalIndex == positional.length && namedIndex == named.length);
       } else {
         positional = new List<Expression>.from(
             arguments.getRange(0, firstNamedArgumentIndex));
         named = new List<NamedExpression>.from(
             arguments.getRange(firstNamedArgumentIndex, arguments.length));
       }

       push(forest.createArguments(beginToken.offset, positional,
           named: named, argumentsOriginalOrder: argumentsOriginalOrder));
     } else {
       // TODO(kmillikin): Find a way to avoid allocating a second list in the
       // case where there were no named arguments, which is a common one.
       push(forest.createArguments(
           beginToken.offset, new List<Expression>.from(arguments),
           argumentsOriginalOrder: argumentsOriginalOrder));
     }
     assert(checkState(beginToken, [ValueKinds.Arguments]));
   }

   @override
   void handleParenthesizedCondition(Token token) {
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
     ]));
     debugEvent("ParenthesizedCondition");
     push(popForValue());
     assert(checkState(token, [ValueKinds.Expression]));
   }

   @override
   void handleParenthesizedExpression(Token token) {
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
     ]));
     debugEvent("ParenthesizedExpression");
     Expression value = popForValue();
     if (value is ShadowLargeIntLiteral) {
       // We need to know that the expression was parenthesized because we will
       // treat -n differently from -(n).  If the expression occurs in a double
       // context, -n is a double literal and -(n) is an application of unary- to
       // an integer literal.  And in any other context, '-' is part of the
       // syntax of -n, i.e., -9223372036854775808 is OK and it is the minimum
       // 64-bit integer, and '-' is an application of unary- in -(n), i.e.,
       // -(9223372036854775808) is an error because the literal does not fit in
       // 64-bits.
       push(value..isParenthesized = true);
     } else {
       push(new ParenthesizedExpressionGenerator(this, token.endGroup!, value));
     }
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
       ]),
     ]));
   }

   @override
   void handleSend(Token beginToken, Token endToken) {
     assert(checkState(beginToken, [
       unionOfKinds([
         ValueKinds.ArgumentsOrNull,
         ValueKinds.ParserRecovery,
       ]),
       ValueKinds.TypeArgumentsOrNull,
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.Identifier,
         ValueKinds.ParserRecovery,
         ValueKinds.ProblemBuilder
       ])
     ]));
     debugEvent("Send");
     Object? arguments = pop();
     List<TypeBuilder>? typeArguments = pop() as List<TypeBuilder>?;
     Object receiver = pop()!;
     // Delay adding [typeArguments] to [forest] for type aliases: They
     // must be unaliased to the type arguments of the denoted type.
     bool isInForest = arguments is Arguments &&
         typeArguments != null &&
         (receiver is! TypeUseGenerator ||
             receiver.declaration is! TypeAliasBuilder);
     if (isInForest) {
       assert(forest.argumentsTypeArguments(arguments).isEmpty);
       forest.argumentsSetTypeArguments(
           arguments,
           buildDartTypeArguments(typeArguments,
               allowPotentiallyConstantType: false));
     } else {
       assert(typeArguments == null ||
           (receiver is TypeUseGenerator &&
               receiver.declaration is TypeAliasBuilder));
     }
     if (receiver is ParserRecovery || arguments is ParserRecovery) {
       push(new ParserErrorGenerator(
           this, beginToken, fasta.messageSyntheticToken));
     } else if (receiver is Identifier) {
       Name name = new Name(receiver.name, libraryBuilder.nameOrigin);
       if (arguments == null) {
         push(new PropertySelector(this, beginToken, name));
       } else {
         push(new InvocationSelector(
             this, beginToken, name, typeArguments, arguments as Arguments,
             isTypeArgumentsInForest: isInForest));
       }
     } else if (arguments == null) {
       push(receiver);
     } else {
       push(finishSend(receiver, typeArguments, arguments as ArgumentsImpl,
           beginToken.charOffset,
           isTypeArgumentsInForest: isInForest));
     }
     assert(checkState(beginToken, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.Initializer,
         ValueKinds.ProblemBuilder,
         ValueKinds.Selector,
       ])
     ]));
   }

   @override
   Expression_Generator_Initializer finishSend(Object receiver,
       List<TypeBuilder>? typeArguments, ArgumentsImpl arguments, int charOffset,
       {bool isTypeArgumentsInForest = false}) {
     if (receiver is Generator) {
       return receiver.doInvocation(charOffset, typeArguments, arguments,
           isTypeArgumentsInForest: isTypeArgumentsInForest);
     } else {
       return forest.createExpressionInvocation(
           charOffset, toValue(receiver), arguments);
     }
   }

   @override
   void beginCascade(Token token) {
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
       ]),
     ]));
     debugEvent("beginCascade");
     Expression expression = popForValue();
     if (expression is Cascade) {
       push(expression);
       push(_createReadOnlyVariableAccess(expression.variable, token,
           expression.fileOffset, null, ReadOnlyAccessKind.LetVariable));
     } else {
       bool isNullAware = optional('?..', token);
       if (isNullAware && !libraryBuilder.isNonNullableByDefault) {
         reportMissingNonNullableSupport(token);
       }
       VariableDeclaration variable =
           createVariableDeclarationForValue(expression);
       push(new Cascade(variable, isNullAware: isNullAware)
         ..fileOffset = expression.fileOffset);
       push(_createReadOnlyVariableAccess(variable, token, expression.fileOffset,
           null, ReadOnlyAccessKind.LetVariable));
     }
     assert(checkState(token, [
       ValueKinds.Generator,
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
       ]),
     ]));
   }

   @override
   void endCascade() {
     assert(checkState(null, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
       ]),
       ValueKinds.Expression,
     ]));
     debugEvent("endCascade");
     Expression expression = popForEffect();
     Cascade cascadeReceiver = pop() as Cascade;
     cascadeReceiver.addCascadeExpression(expression);
     push(cascadeReceiver);
   }

   @override
   void beginCaseExpression(Token caseKeyword) {
     debugEvent("beginCaseExpression");
     super.push(constantContext);
     constantContext = ConstantContext.inferred;
     assert(checkState(caseKeyword, [ValueKinds.ConstantContext]));
   }

   @override
   void endCaseExpression(Token colon) {
     assert(checkState(colon, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
       ValueKinds.ConstantContext,
     ]));
     debugEvent("endCaseExpression");
     Expression expression = popForValue();
     constantContext = pop() as ConstantContext;
     super.push(expression);
     assert(checkState(colon, [ValueKinds.Expression]));
   }

   @override
   void beginBinaryExpression(Token token) {
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
     ]));
     bool isAnd = optional("&&", token);
     if (isAnd || optional("||", token)) {
       Expression lhs = popForValue();
       // This is matched by the call to [endNode] in
       // [doLogicalExpression].
       if (isAnd) {
         typeInferrer.assignedVariables.beginNode();
       }
       push(lhs);
     }
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
     ]));
   }

   @override
   void endBinaryExpression(Token token) {
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
         ValueKinds.Selector,
       ]),
     ]));
     debugEvent("BinaryExpression");
     if (optional(".", token) ||
         optional("..", token) ||
         optional("?..", token)) {
       doDotOrCascadeExpression(token);
     } else if (optional("&&", token) || optional("||", token)) {
       doLogicalExpression(token);
     } else if (optional("??", token)) {
       doIfNull(token);
     } else if (optional("?.", token)) {
       doIfNotNull(token);
     } else {
       doBinaryExpression(token);
     }
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.Initializer,
       ]),
     ]));
   }

   void doBinaryExpression(Token token) {
     assert(checkState(token, <ValueKind>[
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
     ]));
     Expression right = popForValue();
     Object? left = pop();
     int fileOffset = offsetForToken(token);
     String operator = token.stringValue!;
     bool isNot = identical("!=", operator);
     if (isNot || identical("==", operator)) {
       if (left is Generator) {
         push(left.buildEqualsOperation(token, right, isNot: isNot));
       } else {
         if (left is ProblemBuilder) {
           ProblemBuilder problem = left;
           left = buildProblem(problem.message, problem.charOffset, noLength);
         }
         assert(left is Expression);
         push(forest.createEquals(fileOffset, left as Expression, right,
             isNot: isNot));
       }
     } else {
       Name name = new Name(operator);
       if (!isBinaryOperator(operator) && !isMinusOperator(operator)) {
         if (isUserDefinableOperator(operator)) {
           push(buildProblem(
               fasta.templateNotBinaryOperator.withArguments(token),
               token.charOffset,
               token.length));
         } else {
           push(buildProblem(fasta.templateInvalidOperator.withArguments(token),
               token.charOffset, token.length));
         }
       } else if (left is Generator) {
         push(left.buildBinaryOperation(token, name, right));
       } else {
         if (left is ProblemBuilder) {
           ProblemBuilder problem = left;
           left = buildProblem(problem.message, problem.charOffset, noLength);
         }
         assert(left is Expression);
         push(forest.createBinary(fileOffset, left as Expression, name, right));
       }
     }
     assert(checkState(token, <ValueKind>[
       ValueKinds.Expression,
     ]));
   }

   /// Handle `a && b` and `a || b`.
   void doLogicalExpression(Token token) {
     assert(checkState(token, <ValueKind>[
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
     ]));
     Expression argument = popForValue();
     Expression receiver = pop() as Expression;
     Expression logicalExpression = forest.createLogicalExpression(
         offsetForToken(token), receiver, token.stringValue!, argument);
     push(logicalExpression);
     if (optional("&&", token)) {
       // This is matched by the call to [beginNode] in
       // [beginBinaryExpression].
       typeInferrer.assignedVariables.endNode(logicalExpression);
     }
     assert(checkState(token, <ValueKind>[
       ValueKinds.Expression,
     ]));
   }

   /// Handle `a ?? b`.
   void doIfNull(Token token) {
     assert(checkState(token, <ValueKind>[
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
       ]),
     ]));
     Expression b = popForValue();
     Expression a = popForValue();
     push(new IfNullExpression(a, b)..fileOffset = offsetForToken(token));
     assert(checkState(token, <ValueKind>[
       ValueKinds.Expression,
     ]));
   }

   /// Handle `a?.b(...)`.
   void doIfNotNull(Token token) {
     assert(checkState(token, <ValueKind>[
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.Selector,
       ]),
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
         ValueKinds.Initializer,
       ]),
     ]));
     Object? send = pop();
     if (send is Selector) {
       push(send.withReceiver(pop(), token.charOffset, isNullAware: true));
     } else {
       pop();
       token = token.next!;
       push(buildProblem(fasta.templateExpectedIdentifier.withArguments(token),
           offsetForToken(token), lengthForToken(token)));
     }
     assert(checkState(token, <ValueKind>[
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.Initializer,
       ]),
     ]));
   }

   void doDotOrCascadeExpression(Token token) {
     assert(checkState(token, <ValueKind>[
       /* after . or .. */ unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.Selector,
       ]),
       /* before . or .. */ unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
         ValueKinds.Initializer,
       ]),
     ]));
     Object? send = pop();
     if (send is Selector) {
       Object? receiver = optional(".", token) ? pop() : popForValue();
       push(send.withReceiver(receiver, token.charOffset));
     } else if (send is IncompleteErrorGenerator) {
       // Pop the "receiver" and push the error.
       pop();
       push(send);
     } else {
       // Pop the "receiver" and push the error.
       pop();
       token = token.next!;
       push(buildProblem(fasta.templateExpectedIdentifier.withArguments(token),
           offsetForToken(token), lengthForToken(token)));
     }
     assert(checkState(token, <ValueKind>[
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.Initializer,
       ]),
     ]));
   }

   bool areArgumentsCompatible(FunctionNode function, Arguments arguments) {
     // TODO(ahe): Implement this.
     return true;
   }

   @override
   Expression buildUnresolvedError(
       Expression receiver, String name, Arguments arguments, int charOffset,
       {Member? candidate,
       bool isSuper: false,
       required UnresolvedKind kind,
       bool isStatic: false,
       LocatedMessage? message}) {
     int length = name.length;
     int periodIndex = name.lastIndexOf(".");
     if (periodIndex != -1) {
       length -= periodIndex + 1;
     }
     Name kernelName = new Name(name, libraryBuilder.nameOrigin);
     List<LocatedMessage>? context;
     if (candidate != null && candidate.location != null) {
       Uri uri = candidate.location!.file;
       int offset = candidate.fileOffset;
       Message contextMessage;
       int length = noLength;
       if (candidate is Constructor && candidate.isSynthetic) {
         offset = candidate.enclosingClass.fileOffset;
         contextMessage = fasta.templateCandidateFoundIsDefaultConstructor
             .withArguments(candidate.enclosingClass.name);
       } else {
         if (candidate is Constructor) {
           if (candidate.name.text == '') {
             length = candidate.enclosingClass.name.length;
           } else {
             // Assume no spaces around the dot. Not perfect, but probably the
             // best we can do with the information available.
             length = candidate.enclosingClass.name.length + 1 + name.length;
           }
         } else {
           length = name.length;
         }
         contextMessage = fasta.messageCandidateFound;
       }
       context = [contextMessage.withLocation(uri, offset, length)];
     }
     if (message == null) {
       switch (kind) {
         case UnresolvedKind.Unknown:
           assert(!isSuper);
           message = fasta.templateNameNotFound
               .withArguments(name)
               .withLocation(uri, charOffset, length);
           break;
         case UnresolvedKind.Member:
           message = warnUnresolvedMember(kernelName, charOffset,
                   isSuper: isSuper, reportWarning: false, context: context)
               .withLocation(uri, charOffset, length);
           break;
         case UnresolvedKind.Getter:
           message = warnUnresolvedGet(kernelName, charOffset,
                   isSuper: isSuper, reportWarning: false, context: context)
               .withLocation(uri, charOffset, length);
           break;
         case UnresolvedKind.Setter:
           message = warnUnresolvedSet(kernelName, charOffset,
                   isSuper: isSuper, reportWarning: false, context: context)
               .withLocation(uri, charOffset, length);
           break;
         case UnresolvedKind.Method:
           message = warnUnresolvedMethod(kernelName, charOffset,
                   isSuper: isSuper, reportWarning: false, context: context)
               .withLocation(uri, charOffset, length);
           break;
         case UnresolvedKind.Constructor:
           message = warnUnresolvedConstructor(kernelName, isSuper: isSuper)
               .withLocation(uri, charOffset, length);
           break;
       }
     }
     return buildProblem(
         message.messageObject, message.charOffset, message.length,
         context: context);
   }

   Message warnUnresolvedMember(Name name, int charOffset,
       {bool isSuper: false,
       bool reportWarning: true,
       List<LocatedMessage>? context}) {
     Message message = isSuper
         ? fasta.templateSuperclassHasNoMember.withArguments(name.text)
         : fasta.templateMemberNotFound.withArguments(name.text);
     if (reportWarning) {
       addProblemErrorIfConst(message, charOffset, name.text.length,
           context: context);
     }
     return message;
   }

   @override
   Message warnUnresolvedGet(Name name, int charOffset,
       {bool isSuper: false,
       bool reportWarning: true,
       List<LocatedMessage>? context}) {
     Message message = isSuper
         ? fasta.templateSuperclassHasNoGetter.withArguments(name.text)
         : fasta.templateGetterNotFound.withArguments(name.text);
     if (reportWarning) {
       addProblemErrorIfConst(message, charOffset, name.text.length,
           context: context);
     }
     return message;
   }

   @override
   Message warnUnresolvedSet(Name name, int charOffset,
       {bool isSuper: false,
       bool reportWarning: true,
       List<LocatedMessage>? context}) {
     Message message = isSuper
         ? fasta.templateSuperclassHasNoSetter.withArguments(name.text)
         : fasta.templateSetterNotFound.withArguments(name.text);
     if (reportWarning) {
       addProblemErrorIfConst(message, charOffset, name.text.length,
           context: context);
     }
     return message;
   }

   @override
   Message warnUnresolvedMethod(Name name, int charOffset,
       {bool isSuper: false,
       bool reportWarning: true,
       List<LocatedMessage>? context}) {
     String plainName = name.text;

     int dotIndex = plainName.lastIndexOf(".");
     if (dotIndex != -1) {
       plainName = plainName.substring(dotIndex + 1);
     }
     // TODO(ahe): This is rather brittle. We would probably be better off with
     // more precise location information in this case.
     int length = plainName.length;
     if (plainName.startsWith("[")) {
       length = 1;
     }
     Message message = isSuper
         ? fasta.templateSuperclassHasNoMethod.withArguments(name.text)
         : fasta.templateMethodNotFound.withArguments(name.text);
     if (reportWarning) {
       addProblemErrorIfConst(message, charOffset, length, context: context);
     }
     return message;
   }

   Message warnUnresolvedConstructor(Name name, {bool isSuper: false}) {
     Message message = isSuper
         ? fasta.templateSuperclassHasNoConstructor.withArguments(name.text)
         : fasta.templateConstructorNotFound.withArguments(name.text);
     return message;
   }

   @override
   void warnTypeArgumentsMismatch(String name, int expected, int charOffset) {
     addProblemErrorIfConst(
         fasta.templateTypeArgumentMismatch.withArguments(expected),
         charOffset,
         name.length);
   }

   @override
   Member? lookupInstanceMember(Name name,
       {bool isSetter: false, bool isSuper: false}) {
     return classBuilder!.lookupInstanceMember(hierarchy, name,
         isSetter: isSetter, isSuper: isSuper);
   }

   @override
   Constructor? lookupConstructor(Name name, {bool isSuper: false}) {
     return classBuilder!.lookupConstructor(name, isSuper: isSuper);
   }

   @override
   void handleIdentifier(Token token, IdentifierContext context) {
     debugEvent("handleIdentifier");
     String name = token.lexeme;
     if (context.isScopeReference) {
       assert(!inInitializerLeftHandSide ||
           this.scope == enclosingScope ||
           this.scope.parent == enclosingScope);
       // This deals with this kind of initializer: `C(a) : a = a;`
       Scope scope = inInitializerLeftHandSide ? enclosingScope : this.scope;
       push(scopeLookup(scope, name, token));
     } else {
       if (!context.inDeclaration &&
           constantContext != ConstantContext.none &&
           !context.allowedInConstantExpression) {
         addProblem(fasta.messageNotAConstantExpression, token.charOffset,
             token.length);
       }
       if (token.isSynthetic) {
         push(new ParserRecovery(offsetForToken(token)));
       } else {
         push(new Identifier(token));
       }
     }
     assert(checkState(token, [
       unionOfKinds([
         ValueKinds.Identifier,
         ValueKinds.Generator,
         ValueKinds.ParserRecovery,
         ValueKinds.ProblemBuilder,
       ]),
     ]));
   }

   /// Helper method to create a [VariableGet] of the [variable] using
   /// [charOffset] as the file offset.
   @override
   VariableGet createVariableGet(VariableDeclaration variable, int charOffset,
       {bool forNullGuardedAccess: false}) {
     if (!(variable as VariableDeclarationImpl).isLocalFunction) {
       typeInferrer.assignedVariables.read(variable);
     }
     return new VariableGetImpl(variable,
         forNullGuardedAccess: forNullGuardedAccess)
       ..fileOffset = charOffset;
   }

   /// Helper method to create a [ReadOnlyAccessGenerator] on the [variable]
   /// using [token] and [charOffset] for offset information and [name]
   /// for `ExpressionGenerator._plainNameForRead`.
   ReadOnlyAccessGenerator _createReadOnlyVariableAccess(
       VariableDeclaration variable,
       Token token,
       int charOffset,
       String? name,
       ReadOnlyAccessKind kind) {
     return new ReadOnlyAccessGenerator(
         this, token, createVariableGet(variable, charOffset), name ?? '', kind);
   }

   /// Look up [name] in [scope] using [token] as location information (both to
   /// report problems and as the file offset in the generated kernel code).
   /// [isQualified] should be true if [name] is a qualified access (which
   /// implies that it shouldn't be turned into a [ThisPropertyAccessGenerator]
   /// if the name doesn't resolve in the scope).
   @override
   Expression_Generator_Builder scopeLookup(
       Scope scope, String name, Token token,
       {bool isQualified: false, PrefixBuilder? prefix}) {
     int charOffset = offsetForToken(token);
     if (token.isSynthetic) {
       return new ParserErrorGenerator(this, token, fasta.messageSyntheticToken);
     }
     Builder? declaration = scope.lookup(name, charOffset, uri);
     if (declaration == null &&
         prefix == null &&
         (classBuilder?.isPatch ?? false)) {
       // The scope of a patched method includes the origin class.
       declaration = classBuilder!.origin
           .findStaticBuilder(name, charOffset, uri, libraryBuilder);
     }
     if (declaration != null &&
         declaration.isDeclarationInstanceMember &&
         (inFieldInitializer && !inLateFieldInitializer) &&
         !inInitializerLeftHandSide) {
       // We cannot access a class instance member in an initializer of a
       // field.
       //
       // For instance
       //
       //     class M {
       //       int foo = bar;
       //       int bar;
       //     }
       //
       return new IncompleteErrorGenerator(this, token,
           fasta.templateThisAccessInFieldInitializer.withArguments(name));
     }
     if (declaration == null ||
         (!isDeclarationInstanceContext &&
             declaration.isDeclarationInstanceMember)) {
       // We either didn't find a declaration or found an instance member from
       // a non-instance context.
       Name n = new Name(name, libraryBuilder.nameOrigin);
       if (!isQualified && isDeclarationInstanceContext) {
         assert(declaration == null);
         if (constantContext != ConstantContext.none ||
             (inFieldInitializer && !inLateFieldInitializer) &&
                 !inInitializerLeftHandSide) {
           return new UnresolvedNameGenerator(this, token, n,
               unresolvedReadKind: UnresolvedKind.Unknown);
         }
         if (extensionThis != null) {
           // If we are in an extension instance member we interpret this as an
           // implicit access on the 'this' parameter.
           return PropertyAccessGenerator.make(this, token,
               createVariableGet(extensionThis!, charOffset), n, false);
         } else {
           // This is an implicit access on 'this'.
           return new ThisPropertyAccessGenerator(this, token, n);
         }
       } else if (ignoreMainInGetMainClosure &&
           name == "main" &&
           member.name == "_getMainClosure") {
         return forest.createNullLiteral(charOffset);
       } else {
         return new UnresolvedNameGenerator(this, token, n,
             unresolvedReadKind: UnresolvedKind.Unknown);
       }
     } else if (declaration.isTypeDeclaration) {
       if (declaration is AccessErrorBuilder) {
         AccessErrorBuilder accessError = declaration;
         declaration = accessError.builder;
       }
       return new TypeUseGenerator(
           this, token, declaration as TypeDeclarationBuilder, name);
     } else if (declaration.isLocal) {
       VariableBuilder variableBuilder = declaration as VariableBuilder;
       if (constantContext != ConstantContext.none &&
           !variableBuilder.isConst &&
           !member.isConstructor &&
           !enableConstFunctionsInLibrary) {
         return new IncompleteErrorGenerator(
             this, token, fasta.messageNotAConstantExpression);
       }
       VariableDeclaration variable = variableBuilder.variable!;
       if (!variableBuilder.isAssignable) {
         return _createReadOnlyVariableAccess(
             variable,
             token,
             charOffset,
             name,
             variableBuilder.isConst
                 ? ReadOnlyAccessKind.ConstVariable
                 : ReadOnlyAccessKind.FinalVariable);
       } else {
         return new VariableUseGenerator(this, token, variable);
       }
     } else if (declaration.isClassInstanceMember) {
       if (constantContext != ConstantContext.none &&
           !inInitializerLeftHandSide &&
           // TODO(ahe): This is a hack because Fasta sets up the scope
           // "this.field" parameters according to old semantics. Under the new
           // semantics, such parameters introduces a new parameter with that
           // name that should be resolved here.
           !member.isConstructor) {
         addProblem(
             fasta.messageNotAConstantExpression, charOffset, token.length);
       }
       Name n = new Name(name, libraryBuilder.nameOrigin);
       return new ThisPropertyAccessGenerator(this, token, n);
     } else if (declaration.isExtensionInstanceMember) {
       ExtensionBuilder extensionBuilder =
           declarationBuilder as ExtensionBuilder;
       MemberBuilder? setterBuilder =
           _getCorrespondingSetterBuilder(scope, declaration, name, charOffset);
       // TODO(johnniwinther): Check for constantContext like below?
       if (declaration.isField) {
         declaration = null;
       }
       if (setterBuilder != null &&
           (setterBuilder.isField || setterBuilder.isStatic)) {
         setterBuilder = null;
       }
       if (declaration == null && setterBuilder == null) {
         return new UnresolvedNameGenerator(
             this, token, new Name(name, libraryBuilder.nameOrigin),
             unresolvedReadKind: UnresolvedKind.Unknown);
       }
       MemberBuilder? getterBuilder =
           declaration is MemberBuilder ? declaration : null;
       return new ExtensionInstanceAccessGenerator.fromBuilder(
           this,
           token,
           extensionBuilder.extension,
           name,
           extensionThis!,
           extensionTypeParameters,
           getterBuilder,
           setterBuilder);
     } else if (declaration.isRegularMethod) {
       assert(declaration.isStatic || declaration.isTopLevel);
       MemberBuilder memberBuilder = declaration as MemberBuilder;
       return new StaticAccessGenerator(
           this, token, name, memberBuilder.member, null);
     } else if (declaration is PrefixBuilder) {
       assert(prefix == null);
       return new PrefixUseGenerator(this, token, declaration);
     } else if (declaration is LoadLibraryBuilder) {
       return new LoadLibraryGenerator(this, token, declaration);
     } else if (declaration.hasProblem && declaration is! AccessErrorBuilder) {
       return declaration;
     } else {
       MemberBuilder? setterBuilder =
           _getCorrespondingSetterBuilder(scope, declaration, name, charOffset);
       MemberBuilder? getterBuilder =
           declaration is MemberBuilder ? declaration : null;
       assert(getterBuilder != null || setterBuilder != null);
       StaticAccessGenerator generator = new StaticAccessGenerator.fromBuilder(
           this, name, token, getterBuilder, setterBuilder);
       if (constantContext != ConstantContext.none) {
         Member? readTarget = generator.readTarget;
         if (!(readTarget is Field && readTarget.isConst ||
             // Static tear-offs are also compile time constants.
             readTarget is Procedure)) {
           addProblem(
               fasta.messageNotAConstantExpression, charOffset, token.length);
         }
       }
       return generator;
     }
   }

   /// Returns the setter builder corresponding to [declaration] using the
   /// [name] and [charOffset] for the lookup into [scope] if necessary.
   MemberBuilder? _getCorrespondingSetterBuilder(
       Scope scope, Builder declaration, String name, int charOffset) {
     Builder? setter;
     if (declaration.isSetter) {
       setter = declaration;
     } else if (declaration.isGetter) {
       setter = scope.lookupSetter(name, charOffset, uri);
     } else if (declaration.isField) {
       MemberBuilder fieldBuilder = declaration as MemberBuilder;
       if (!fieldBuilder.isAssignable) {
         setter = scope.lookupSetter(name, charOffset, uri);
       } else {
         setter = declaration;
       }
     }
     return setter is MemberBuilder ? setter : null;
   }

   @override
   void handleQualified(Token period) {
     debugEvent("Qualified");
     Object? node = pop();
     Object? qualifier = pop();
     if (qualifier is ParserRecovery) {
       push(qualifier);
     } else if (node is ParserRecovery) {
       push(node);
     } else {
       Identifier identifier = node as Identifier;
       push(identifier.withQualifier(qualifier!));
     }
   }

   @override
   void beginLiteralString(Token token) {
     debugEvent("beginLiteralString");
     push(token);
   }

   @override
   void handleStringPart(Token token) {
     debugEvent("StringPart");
     push(token);
   }

   @override
   void endLiteralString(int interpolationCount, Token endToken) {
     debugEvent("endLiteralString");
     if (interpolationCount == 0) {
       Token token = pop() as Token;
       String value = unescapeString(token.lexeme, token, this);
       push(forest.createStringLiteral(offsetForToken(token), value));
     } else {
       int count = 1 + interpolationCount * 2;
       List<Object>? parts = const FixedNullableList<Object>()
           .popNonNullable(stack, count, /* dummyValue = */ 0);
       if (parts == null) {
         push(new ParserRecovery(endToken.charOffset));
         return;
       }
       Token first = parts.first as Token;
       Token last = parts.last as Token;
       Quote quote = analyzeQuote(first.lexeme);
       List<Expression> expressions = <Expression>[];
       // Contains more than just \' or \".
       if (first.lexeme.length > 1) {
         String value =
             unescapeFirstStringPart(first.lexeme, quote, first, this);
         if (value.isNotEmpty) {
           expressions
               .add(forest.createStringLiteral(offsetForToken(first), value));
         }
       }
       for (int i = 1; i < parts.length - 1; i++) {
         Object part = parts[i];
         if (part is Token) {
           if (part.lexeme.length != 0) {
             String value = unescape(part.lexeme, quote, part, this);
             expressions
                 .add(forest.createStringLiteral(offsetForToken(part), value));
           }
         } else {
           expressions.add(toValue(part));
         }
       }
       // Contains more than just \' or \".
       if (last.lexeme.length > 1) {
         String value = unescapeLastStringPart(
             last.lexeme, quote, last, last.isSynthetic, this);
         if (value.isNotEmpty) {
           expressions
               .add(forest.createStringLiteral(offsetForToken(last), value));
         }
       }
       push(forest.createStringConcatenation(
           offsetForToken(endToken), expressions));
     }
   }

   @override
   void handleNativeClause(Token nativeToken, bool hasName) {
     debugEvent("NativeClause");
     if (hasName) {
       pop() as StringLiteral;
     }
   }

   @override
   void handleScript(Token token) {
     debugEvent("Script");
   }

   @override
   void handleStringJuxtaposition(Token startToken, int literalCount) {
     debugEvent("StringJuxtaposition");
     List<Expression> parts = popListForValue(literalCount);
     List<Expression>? expressions;
     // Flatten string juxtapositions of string interpolation.
     for (int i = 0; i < parts.length; i++) {
       Expression part = parts[i];
       if (part is StringConcatenation) {
         if (expressions == null) {
           expressions = parts.sublist(0, i);
         }
         for (Expression expression in part.expressions) {
           expressions.add(expression);
         }
       } else {
         if (expressions != null) {
           expressions.add(part);
         }
       }
     }
     push(forest.createStringConcatenation(
         offsetForToken(startToken), expressions ?? parts));
   }

   @override
   void handleLiteralInt(Token token) {
     debugEvent("LiteralInt");
     int? value = int.tryParse(token.lexeme);
     // Postpone parsing of literals resulting in a negative value
     // (hex literals >= 2^63). These are only allowed when not negated.
     if (value == null || value < 0) {
       push(forest.createIntLiteralLarge(offsetForToken(token), token.lexeme));
     } else {
       push(forest.createIntLiteral(offsetForToken(token), value, token.lexeme));
     }
   }

   @override
   void handleEmptyFunctionBody(Token semicolon) {
     debugEvent("ExpressionFunctionBody");
     endBlockFunctionBody(0, null, semicolon);
   }

   @override
   void handleExpressionFunctionBody(Token arrowToken, Token? endToken) {
     debugEvent("ExpressionFunctionBody");
     endReturnStatement(true, arrowToken.next!, endToken);
   }

   @override
   void endReturnStatement(
       bool hasExpression, Token beginToken, Token? endToken) {
     debugEvent("ReturnStatement");
     Expression? expression = hasExpression ? popForValue() : null;
     if (expression != null && inConstructor) {
       push(buildProblemStatement(
           fasta.messageConstructorWithReturnType, beginToken.charOffset));
     } else {
       push(forest.createReturnStatement(offsetForToken(beginToken), expression,
           isArrow: !identical(beginToken.lexeme, "return")));
     }
   }

   @override
   void beginThenStatement(Token token) {
     Expression condition = popForValue();
     // This is matched by the call to [deferNode] in
     // [endThenStatement].
     typeInferrer.assignedVariables.beginNode();
     push(condition);
     super.beginThenStatement(token);
   }

   @override
   void endThenStatement(Token token) {
     super.endThenStatement(token);
     // This is matched by the call to [beginNode] in
     // [beginThenStatement] and by the call to [storeInfo] in
     // [endIfStatement].
     push(typeInferrer.assignedVariables.deferNode());
   }

   @override
   void endIfStatement(Token ifToken, Token? elseToken) {
     Statement? elsePart = popStatementIfNotNull(elseToken);
     AssignedVariablesNodeInfo<VariableDeclaration> assignedVariablesInfo =
         pop() as AssignedVariablesNodeInfo<VariableDeclaration>;
     Statement thenPart = popStatement();
     Expression condition = pop() as Expression;
     Statement node = forest.createIfStatement(
         offsetForToken(ifToken), condition, thenPart, elsePart);
     // This is matched by the call to [deferNode] in
     // [endThenStatement].
     typeInferrer.assignedVariables.storeInfo(node, assignedVariablesInfo);
     push(node);
   }

   @override
   void beginVariableInitializer(Token token) {
     if ((currentLocalVariableModifiers & lateMask) != 0) {
       // This is matched by the call to [endNode] in [endVariableInitializer].
       typeInferrer.assignedVariables.beginNode();
     }
   }

   @override
   void endVariableInitializer(Token assignmentOperator) {
     debugEvent("VariableInitializer");
     assert(assignmentOperator.stringValue == "=");
     AssignedVariablesNodeInfo<VariableDeclaration>? assignedVariablesInfo;
     bool isLate = (currentLocalVariableModifiers & lateMask) != 0;
     Expression initializer = popForValue();
     if (isLate) {
       assignedVariablesInfo = typeInferrer.assignedVariables
           .deferNode(isClosureOrLateVariableInitializer: true);
     }
     pushNewLocalVariable(initializer, equalsToken: assignmentOperator);
     if (isLate) {
       VariableDeclaration node = peek() as VariableDeclaration;
       // This is matched by the call to [beginNode] in
       // [beginVariableInitializer].
       typeInferrer.assignedVariables.storeInfo(node, assignedVariablesInfo!);
     }
   }

   @override
   void handleNoVariableInitializer(Token token) {
     debugEvent("NoVariableInitializer");
     bool isConst = (currentLocalVariableModifiers & constMask) != 0;
     bool isFinal = (currentLocalVariableModifiers & finalMask) != 0;
     bool isLate = (currentLocalVariableModifiers & lateMask) != 0;
     Expression? initializer;
     if (!optional("in", token.next!)) {
       // A for-in loop-variable can't have an initializer. So let's remain
       // silent if the next token is `in`. Since a for-in loop can only have
       // one variable it must be followed by `in`.
       if (!token.isSynthetic) {
         // If [token] is synthetic it is created from error recovery.
         if (isConst) {
           initializer = buildProblem(
               fasta.templateConstFieldWithoutInitializer
                   .withArguments(token.lexeme),
               token.charOffset,
               token.length);
         } else if (!libraryBuilder.isNonNullableByDefault &&
             isFinal &&
             !isLate) {
           initializer = buildProblem(
               fasta.templateFinalFieldWithoutInitializer
                   .withArguments(token.lexeme),
               token.charOffset,
               token.length);
         }
       }
     }
     pushNewLocalVariable(initializer);
   }

   void pushNewLocalVariable(Expression? initializer, {Token? equalsToken}) {
     Object? node = pop();
     if (node is ParserRecovery) {
       push(node);
       return;
     }
     Identifier identifier = node as Identifier;
     assert(currentLocalVariableModifiers != -1);
     bool isConst = (currentLocalVariableModifiers & constMask) != 0;
     bool isFinal = (currentLocalVariableModifiers & finalMask) != 0;
     bool isLate = (currentLocalVariableModifiers & lateMask) != 0;
     bool isRequired = (currentLocalVariableModifiers & requiredMask) != 0;
     assert(isConst == (constantContext == ConstantContext.inferred));
     VariableDeclaration variable = new VariableDeclarationImpl(
         identifier.name, functionNestingLevel,
         forSyntheticToken: identifier.token.isSynthetic,
         initializer: initializer,
         type: currentLocalVariableType,
         isFinal: isFinal,
         isConst: isConst,
         isLate: isLate,
         isRequired: isRequired,
         hasDeclaredInitializer: initializer != null,
         isStaticLate: libraryBuilder.isNonNullableByDefault &&
             isFinal &&
             initializer == null)
       ..fileOffset = identifier.charOffset
       ..fileEqualsOffset = offsetForToken(equalsToken);
     typeInferrer.assignedVariables.declare(variable);
     libraryBuilder.checkBoundsInVariableDeclaration(
         variable, typeEnvironment, uri);
     push(variable);
   }

   @override
   void beginFieldInitializer(Token token) {
     inFieldInitializer = true;
     constantContext = member.isConst
         ? ConstantContext.inferred
         : !member.isStatic &&
                 classBuilder != null &&
                 classBuilder!.declaresConstConstructor
             ? ConstantContext.required
             : ConstantContext.none;
     if (member is SourceFieldBuilder) {
       SourceFieldBuilder fieldBuilder = member as SourceFieldBuilder;
       inLateFieldInitializer = fieldBuilder.isLate;
       if (fieldBuilder.isAbstract) {
         addProblem(
             fasta.messageAbstractFieldInitializer, token.charOffset, noLength);
       } else if (fieldBuilder.isExternal) {
         addProblem(
             fasta.messageExternalFieldInitializer, token.charOffset, noLength);
       }
     } else {
       inLateFieldInitializer = false;
     }
   }

   @override
   void endFieldInitializer(Token assignmentOperator, Token token) {
     debugEvent("FieldInitializer");
     inFieldInitializer = false;
     inLateFieldInitializer = false;
     assert(assignmentOperator.stringValue == "=");
     push(popForValue());
     constantContext = ConstantContext.none;
   }

   @override
   void handleNoFieldInitializer(Token token) {
     debugEvent("NoFieldInitializer");
     constantContext = member.isConst
         ? ConstantContext.inferred
         : !member.isStatic &&
                 classBuilder != null &&
                 classBuilder!.declaresConstConstructor
             ? ConstantContext.required
             : ConstantContext.none;
     if (constantContext == ConstantContext.inferred) {
       // Creating a null value to prevent the Dart VM from crashing.
       push(forest.createNullLiteral(offsetForToken(token)));
     } else {
       push(NullValue.FieldInitializer);
     }
     constantContext = ConstantContext.none;
   }

   @override
   void endInitializedIdentifier(Token nameToken) {
     // TODO(ahe): Use [InitializedIdentifier] here?
     debugEvent("InitializedIdentifier");
     Object? node = pop();
     if (node is ParserRecovery) {
       push(node);
       return;
     }
     VariableDeclaration variable = node as VariableDeclaration;
     variable.fileOffset = nameToken.charOffset;
     push(variable);
     declareVariable(variable, scope);
   }

   @override
   void beginVariablesDeclaration(
       Token token, Token? lateToken, Token? varFinalOrConst) {
     debugEvent("beginVariablesDeclaration");
     if (!libraryBuilder.isNonNullableByDefault) {
       reportNonNullableModifierError(lateToken);
     }
     TypeBuilder? unresolvedType = pop(NullValue.TypeBuilder) as TypeBuilder?;
     DartType? type = unresolvedType != null
         ? buildDartType(unresolvedType, allowPotentiallyConstantType: false)
         : null;
     int modifiers = (lateToken != null ? lateMask : 0) |
         Modifier.validateVarFinalOrConst(varFinalOrConst?.lexeme);
     _enterLocalState(inLateLocalInitializer: lateToken != null);
     super.push(currentLocalVariableModifiers);
     super.push(currentLocalVariableType ?? NullValue.Type);
     currentLocalVariableType = type;
     currentLocalVariableModifiers = modifiers;
     super.push(constantContext);
     constantContext = ((modifiers & constMask) != 0)
         ? ConstantContext.inferred
         : ConstantContext.none;
   }

   @override
   void endVariablesDeclaration(int count, Token? endToken) {
     debugEvent("VariablesDeclaration");
     if (count == 1) {
       Object? node = pop();
       constantContext = pop() as ConstantContext;
       currentLocalVariableType = pop(NullValue.Type) as DartType?;
       currentLocalVariableModifiers = pop() as int;
       List<Expression>? annotations = pop() as List<Expression>?;
       if (node is ParserRecovery) {
         push(node);
         return;
       }
       VariableDeclaration variable = node as VariableDeclaration;
       if (annotations != null) {
         for (int i = 0; i < annotations.length; i++) {
           variable.addAnnotation(annotations[i]);
         }
         (variablesWithMetadata ??= <VariableDeclaration>[]).add(variable);
       }
       push(variable);
     } else {
       List<VariableDeclaration>? variables =
           const FixedNullableList<VariableDeclaration>()
               .popNonNullable(stack, count, dummyVariableDeclaration);
       constantContext = pop() as ConstantContext;
       currentLocalVariableType = pop(NullValue.Type) as DartType?;
       currentLocalVariableModifiers = pop() as int;
       List<Expression>? annotations = pop() as List<Expression>?;
       if (variables == null) {
         push(new ParserRecovery(offsetForToken(endToken)));
         return;
       }
       if (annotations != null) {
         VariableDeclaration first = variables.first;
         for (int i = 0; i < annotations.length; i++) {
           first.addAnnotation(annotations[i]);
         }
         (multiVariablesWithMetadata ??= <List<VariableDeclaration>>[])
             .add(variables);
       }
       push(forest.variablesDeclaration(variables, uri));
     }
     _exitLocalState();
   }

   /// Stack containing assigned variables info for try statements.
   ///
   /// These are created in [beginTryStatement] and ended in either [beginBlock]
   /// when a finally block starts or in [endTryStatement] when the try statement
   /// ends. Since these need to be associated with the try statement created in
   /// in [endTryStatement] we store them the stack until the try statement is
   /// created.
   Link<AssignedVariablesNodeInfo<VariableDeclaration>> tryStatementInfoStack =
       const Link<AssignedVariablesNodeInfo<VariableDeclaration>>();

   @override
   void beginBlock(Token token, BlockKind blockKind) {
     if (blockKind == BlockKind.tryStatement) {
       // This is matched by the call to [endNode] in [endBlock].
       typeInferrer.assignedVariables.beginNode();
     } else if (blockKind == BlockKind.finallyClause) {
       // This is matched by the call to [beginNode] in [beginTryStatement].
       tryStatementInfoStack = tryStatementInfoStack
           .prepend(typeInferrer.assignedVariables.deferNode());
     }
     super.beginBlock(token, blockKind);
   }

   @override
   void endBlock(
       int count, Token openBrace, Token closeBrace, BlockKind blockKind) {
     debugEvent("Block");
     Statement block = popBlock(count, openBrace, closeBrace);
     exitLocalScope();
     push(block);
     if (blockKind == BlockKind.tryStatement) {
       // This is matched by the call to [beginNode] in [beginBlock].
       typeInferrer.assignedVariables.endNode(block);
     }
   }

   @override
   void handleInvalidTopLevelBlock(Token token) {
     // TODO(danrubel): Consider improved recovery by adding this block
     // as part of a synthetic top level function.
     pop(); // block
   }

   @override
   void handleAssignmentExpression(Token token) {
     assert(checkState(token, [
       unionOfKinds(<ValueKind>[
         ValueKinds.Expression,
         ValueKinds.Generator,
         // TODO(johnniwinther): Avoid problem builders here.
         ValueKinds.ProblemBuilder
       ]),
       unionOfKinds(<ValueKind>[
         ValueKinds.Expression, ValueKinds.Generator,
         // TODO(johnniwinther): Avoid problem builders here.
         ValueKinds.ProblemBuilder
       ])
     ]));
     debugEvent("AssignmentExpression");
     Expression value = popForValue();
     Object? generator = pop();
     if (generator is! Generator) {
       push(buildProblem(fasta.messageNotAnLvalue, offsetForToken(token),
           lengthForToken(token)));
     } else {
       push(new DelayedAssignment(
           this, token, generator, value, token.stringValue!));
     }
   }

   @override
   void enterLoop(int charOffset) {
     if (peek() is LabelTarget) {
       LabelTarget target = peek() as LabelTarget;
       enterBreakTarget(charOffset, target.breakTarget);
       enterContinueTarget(charOffset, target.continueTarget);
     } else {
       enterBreakTarget(charOffset);
       enterContinueTarget(charOffset);
     }
   }

   void exitLoopOrSwitch(Statement statement) {
     if (problemInLoopOrSwitch != null) {
       push(problemInLoopOrSwitch);
       problemInLoopOrSwitch = null;
     } else {
       push(statement);
     }
   }

   List<VariableDeclaration>? _buildForLoopVariableDeclarations(
       variableOrExpression) {
     // TODO(ahe): This can be simplified now that we have the events
     // `handleForInitializer...` events.
     if (variableOrExpression is Generator) {
       variableOrExpression = variableOrExpression.buildForEffect();
     }
     if (variableOrExpression is VariableDeclaration) {
       // Late for loop variables are not supported. An error has already been
       // reported by the parser.
       variableOrExpression.isLate = false;
       return <VariableDeclaration>[variableOrExpression];
     } else if (variableOrExpression is Expression) {
       VariableDeclaration variable =
           new VariableDeclarationImpl.forEffect(variableOrExpression);
       return <VariableDeclaration>[variable];
     } else if (variableOrExpression is ExpressionStatement) {
       VariableDeclaration variable = new VariableDeclarationImpl.forEffect(
           variableOrExpression.expression);
       return <VariableDeclaration>[variable];
     } else if (forest.isVariablesDeclaration(variableOrExpression)) {
       return forest
           .variablesDeclarationExtractDeclarations(variableOrExpression);
     } else if (variableOrExpression is List<Object>) {
       List<VariableDeclaration> variables = <VariableDeclaration>[];
       for (Object v in variableOrExpression) {
         variables.addAll(_buildForLoopVariableDeclarations(v)!);
       }
       return variables;
     } else if (variableOrExpression == null) {
       return <VariableDeclaration>[];
     }
     return null;
   }

   @override
   void handleForInitializerEmptyStatement(Token token) {
     debugEvent("ForInitializerEmptyStatement");
     push(NullValue.Expression);
     // This is matched by the call to [deferNode] in [endForStatement] or
     // [endForControlFlow].
     typeInferrer.assignedVariables.beginNode();
   }

   @override
   void handleForInitializerExpressionStatement(Token token, bool forIn) {
     debugEvent("ForInitializerExpressionStatement");
     if (!forIn) {
       // This is matched by the call to [deferNode] in [endForStatement] or
       // [endForControlFlow].
       typeInferrer.assignedVariables.beginNode();
     }
   }

   @override
   void handleForInitializerLocalVariableDeclaration(Token token, bool forIn) {
     debugEvent("ForInitializerLocalVariableDeclaration");
     if (forIn) {
       // If the declaration is of the form `for (final x in ...)`, then we may
       // have erroneously set the `isStaticLate` flag, so un-set it.
       Object? declaration = peek();
       if (declaration is VariableDeclarationImpl) {
         declaration.isStaticLate = false;
       }
     } else {
       // This is matched by the call to [deferNode] in [endForStatement] or
       // [endForControlFlow].
       typeInferrer.assignedVariables.beginNode();
     }
   }

   @override
   void handleForLoopParts(Token forKeyword, Token leftParen,
       Token leftSeparator, int updateExpressionCount) {
     push(forKeyword);
     push(leftParen);
     push(leftSeparator);
     push(updateExpressionCount);
   }

   @override
   void endForControlFlow(Token token) {
     debugEvent("ForControlFlow");
     Object? entry = pop();
     int updateExpressionCount = pop() as int;
     pop(); // left separator
     pop(); // left parenthesis
     Token forToken = pop() as Token;
     List<Expression> updates = popListForEffect(updateExpressionCount);
     Statement conditionStatement = popStatement(); // condition

     if (constantContext != ConstantContext.none) {
       pop(); // Pop variable or expression.
       exitLocalScope();
       typeInferrer.assignedVariables.discardNode();

       handleRecoverableError(
           fasta.templateCantUseControlFlowOrSpreadAsConstant
               .withArguments(forToken),
           forToken,
           forToken);
       push(invalidCollectionElement);
       return;
     }

     // This is matched by the call to [beginNode] in
     // [handleForInitializerEmptyStatement],
     // [handleForInitializerExpressionStatement], and
     // [handleForInitializerLocalVariableDeclaration].
     AssignedVariablesNodeInfo<VariableDeclaration> assignedVariablesNodeInfo =
         typeInferrer.assignedVariables.popNode();

     Object? variableOrExpression = pop();
     exitLocalScope();

     transformCollections = true;
     List<VariableDeclaration> variables =
         _buildForLoopVariableDeclarations(variableOrExpression)!;
     typeInferrer.assignedVariables.pushNode(assignedVariablesNodeInfo);
     Expression? condition;
     if (conditionStatement is ExpressionStatement) {
       condition = conditionStatement.expression;
     } else {
       assert(conditionStatement is EmptyStatement);
     }
     if (entry is MapLiteralEntry) {
       ForMapEntry result = forest.createForMapEntry(
           offsetForToken(forToken), variables, condition, updates, entry);
       typeInferrer.assignedVariables.endNode(result);
       push(result);
     } else {
       ForElement result = forest.createForElement(offsetForToken(forToken),
           variables, condition, updates, toValue(entry));
       typeInferrer.assignedVariables.endNode(result);
       push(result);
     }
   }

   @override
   void endForStatement(Token endToken) {
     assert(checkState(endToken, <ValueKind>[
       /* body */ ValueKinds.Statement,
       /* expression count */ ValueKinds.Integer,
       /* left separator */ ValueKinds.Token,
       /* left parenthesis */ ValueKinds.Token,
       /* for keyword */ ValueKinds.Token,
     ]));
     debugEvent("ForStatement");
     Statement body = popStatement();

     int updateExpressionCount = pop() as int;
     pop(); // Left separator.
     pop(); // Left parenthesis.
     Token forKeyword = pop() as Token;

     assert(checkState(endToken, <ValueKind>[
       /* expressions */ ...repeatedKinds(
           unionOfKinds(
               <ValueKind>[ValueKinds.Expression, ValueKinds.Generator]),
           updateExpressionCount),
       /* condition */ ValueKinds.Statement,
       /* variable or expression */ unionOfKinds(<ValueKind>[
         ValueKinds.Generator,
         ValueKinds.ExpressionOrNull,
         ValueKinds.Statement,
         ValueKinds.ObjectList,
         ValueKinds.ParserRecovery,
       ]),
     ]));

     List<Expression> updates = popListForEffect(updateExpressionCount);
     Statement conditionStatement = popStatement();
     // This is matched by the call to [beginNode] in
     // [handleForInitializerEmptyStatement],
     // [handleForInitializerExpressionStatement], and
     // [handleForInitializerLocalVariableDeclaration].
     AssignedVariablesNodeInfo<VariableDeclaration> assignedVariablesNodeInfo =
         typeInferrer.assignedVariables.deferNode();

     Object? variableOrExpression = pop();
     List<VariableDeclaration>? variables =
         _buildForLoopVariableDeclarations(variableOrExpression);
     exitLocalScope();
     JumpTarget continueTarget = exitContinueTarget() as JumpTarget;
     JumpTarget breakTarget = exitBreakTarget() as JumpTarget;
     List<BreakStatementImpl>? continueStatements;
     if (continueTarget.hasUsers) {
       LabeledStatement labeledStatement = forest.createLabeledStatement(body);
       continueStatements =
           continueTarget.resolveContinues(forest, labeledStatement);
       body = labeledStatement;
     }
     Expression? condition;
     if (conditionStatement is ExpressionStatement) {
       condition = conditionStatement.expression;
     } else {
       assert(conditionStatement is EmptyStatement);
     }
     Statement forStatement = forest.createForStatement(
         offsetForToken(forKeyword), variables, condition, updates, body);
     typeInferrer.assignedVariables
         .storeInfo(forStatement, assignedVariablesNodeInfo);
     if (continueStatements != null) {
       for (BreakStatementImpl continueStatement in continueStatements) {
         continueStatement.targetStatement = forStatement;
       }
     }
     Statement result = forStatement;
     if (breakTarget.hasUsers) {
       LabeledStatement labeledStatement = forest.createLabeledStatement(result);
       breakTarget.resolveBreaks(forest, labeledStatement, forStatement);
       result = labeledStatement;
     }
     if (variableOrExpression is ParserRecovery) {
       problemInLoopOrSwitch ??= buildProblemStatement(
           fasta.messageSyntheticToken, variableOrExpression.charOffset,
           suppressMessage: true);
     }
     exitLoopOrSwitch(result);
   }

   @override
   void endAwaitExpression(Token keyword, Token endToken) {
     debugEvent("AwaitExpression");
     int fileOffset = offsetForToken(keyword);
     Expression value = popForValue();
     if (inLateLocalInitializer) {
       push(buildProblem(fasta.messageAwaitInLateLocalInitializer, fileOffset,
           keyword.charCount));
     } else {
       push(forest.createAwaitExpression(fileOffset, value));
     }
   }

   @override
   void endInvalidAwaitExpression(
       Token keyword, Token endToken, fasta.MessageCode errorCode) {
     debugEvent("AwaitExpression");
     popForValue();
     push(buildProblem(errorCode, keyword.offset, keyword.length));
   }

   @override
   void endInvalidYieldStatement(Token keyword, Token? starToken, Token endToken,
       fasta.MessageCode errorCode) {
     debugEvent("YieldStatement");
     popForValue();
     push(buildProblemStatement(errorCode, keyword.offset));
   }

   @override
   void handleAsyncModifier(Token? asyncToken, Token? starToken) {
     debugEvent("AsyncModifier");
     push(asyncMarkerFromTokens(asyncToken, starToken));
   }

   @override
   void handleLiteralList(
       int count, Token leftBracket, Token? constKeyword, Token rightBracket) {
     debugEvent("LiteralList");

     if (constantContext == ConstantContext.required && constKeyword == null) {
       addProblem(fasta.messageMissingExplicitConst, offsetForToken(leftBracket),
           noLength);
     }

     // TODO(danrubel): Replace this with popListForValue
     // when control flow and spread collections have been enabled by default
     List<Expression> expressions =
         new List<Expression>.filled(count, dummyExpression, growable: true);
     for (int i = count - 1; i >= 0; i--) {
       Object? elem = pop();
       if (elem != invalidCollectionElement) {
         expressions[i] = toValue(elem);
       } else {
         expressions.removeAt(i);
       }
     }

     List<TypeBuilder>? typeArguments = pop() as List<TypeBuilder>?;

     DartType typeArgument;
     if (typeArguments != null) {
       if (typeArguments.length > 1) {
         addProblem(
             fasta.messageListLiteralTooManyTypeArguments,
             offsetForToken(leftBracket),
             lengthOfSpan(leftBracket, leftBracket.endGroup));
         typeArgument = const InvalidType();
       } else {
         typeArgument = buildDartType(typeArguments.single,
             allowPotentiallyConstantType: false);
         typeArgument = instantiateToBounds(
             typeArgument, coreTypes.objectClass, libraryBuilder.library);
       }
     } else {
       typeArgument = implicitTypeArgument;
     }

     ListLiteral node = forest.createListLiteral(
         // TODO(johnniwinther): The file offset computed below will not be
         // correct if there are type arguments but no `const` keyword.
         offsetForToken(constKeyword ?? leftBracket),
         typeArgument,
         expressions,
         isConst: constKeyword != null ||
             constantContext == ConstantContext.inferred);
     libraryBuilder.checkBoundsInListLiteral(node, typeEnvironment, uri);
     push(node);
   }

   void buildLiteralSet(List<TypeBuilder>? typeArguments, Token? constKeyword,
       Token leftBrace, List<dynamic>? setOrMapEntries) {
     DartType typeArgument;
     if (typeArguments != null) {
       typeArgument = buildDartType(typeArguments.single,
           allowPotentiallyConstantType: false);
       typeArgument = instantiateToBounds(
           typeArgument, coreTypes.objectClass, libraryBuilder.library);
     } else {
       typeArgument = implicitTypeArgument;
     }

     List<Expression> expressions = <Expression>[];
     if (setOrMapEntries != null) {
       for (dynamic entry in setOrMapEntries) {
         if (entry is MapLiteralEntry) {
           // TODO(danrubel): report the error on the colon
           addProblem(fasta.templateExpectedButGot.withArguments(','),
               entry.fileOffset, 1);
         } else {
           // TODO(danrubel): Revise once control flow and spread
           //  collection entries are supported.
           expressions.add(entry as Expression);
         }
       }
     }

     SetLiteral node = forest.createSetLiteral(
         // TODO(johnniwinther): The file offset computed below will not be
         // correct if there are type arguments but no `const` keyword.
         offsetForToken(constKeyword ?? leftBrace),
         typeArgument,
         expressions,
         isConst: constKeyword != null ||
             constantContext == ConstantContext.inferred);
     libraryBuilder.checkBoundsInSetLiteral(node, typeEnvironment, uri);
     push(node);
   }

   @override
   void handleLiteralSetOrMap(
     int count,
     Token leftBrace,
     Token? constKeyword,
     Token rightBrace,
     // TODO(danrubel): hasSetEntry parameter exists for replicating existing
     // behavior and will be removed once unified collection has been enabled
     bool hasSetEntry,
   ) {
     debugEvent("LiteralSetOrMap");

     if (constantContext == ConstantContext.required && constKeyword == null) {
       addProblem(fasta.messageMissingExplicitConst, offsetForToken(leftBrace),
           noLength);
     }

     List<dynamic> setOrMapEntries =
         new List<dynamic>.filled(count, null, growable: true);
     for (int i = count - 1; i >= 0; i--) {
       Object? elem = pop();
       // TODO(danrubel): Revise this to handle control flow and spread
       if (elem == invalidCollectionElement) {
         setOrMapEntries.removeAt(i);
       } else if (elem is MapLiteralEntry) {
         setOrMapEntries[i] = elem;
       } else {
         setOrMapEntries[i] = toValue(elem);
       }
     }
     List<TypeBuilder>? typeArguments = pop() as List<TypeBuilder>?;

     // Replicate existing behavior that has been removed from the parser.
     // This will be removed once unified collections is implemented.

     // Determine if this is a set or map based on type args and content
     // TODO(danrubel): Since type resolution is needed to disambiguate
     // set or map in some situations, consider always deferring determination
     // until the type resolution phase.
     final int? typeArgCount = typeArguments?.length;
     bool? isSet = typeArgCount == 1
         ? true
         : typeArgCount != null
             ? false
             : null;

     for (int i = 0; i < setOrMapEntries.length; ++i) {
       if (setOrMapEntries[i] is! MapLiteralEntry &&
           !isConvertibleToMapEntry(setOrMapEntries[i])) {
         hasSetEntry = true;
       }
     }

     // TODO(danrubel): If the type arguments are not known (null) then
     // defer set/map determination until after type resolution as per the
     // unified collection spec: https://github.com/dart-lang/language/pull/200
     // rather than trying to guess as done below.
     isSet ??= hasSetEntry;

     if (isSet) {
       buildLiteralSet(typeArguments, constKeyword, leftBrace, setOrMapEntries);
     } else {
       List<MapLiteralEntry> mapEntries = new List<MapLiteralEntry>.filled(
           setOrMapEntries.length, dummyMapLiteralEntry);
       for (int i = 0; i < setOrMapEntries.length; ++i) {
         if (setOrMapEntries[i] is MapLiteralEntry) {
           mapEntries[i] = setOrMapEntries[i];
         } else {
           mapEntries[i] = convertToMapEntry(setOrMapEntries[i], this,
               typeInferrer.assignedVariables.reassignInfo);
         }
       }
       buildLiteralMap(typeArguments, constKeyword, leftBrace, mapEntries);
     }
   }

   @override
   void handleLiteralBool(Token token) {
     debugEvent("LiteralBool");
     bool value = optional("true", token);
     assert(value || optional("false", token));
     push(forest.createBoolLiteral(offsetForToken(token), value));
   }

   @override
   void handleLiteralDouble(Token token) {
     debugEvent("LiteralDouble");
     push(forest.createDoubleLiteral(
         offsetForToken(token), double.parse(token.lexeme)));
   }

   @override
   void handleLiteralNull(Token token) {
     debugEvent("LiteralNull");
     push(forest.createNullLiteral(offsetForToken(token)));
   }

   void buildLiteralMap(List<TypeBuilder>? typeArguments, Token? constKeyword,
       Token leftBrace, List<MapLiteralEntry> entries) {
     DartType keyType;
     DartType valueType;
     if (typeArguments != null) {
       if (typeArguments.length != 2) {
         keyType = const InvalidType();
         valueType = const InvalidType();
       } else {
         keyType = buildDartType(typeArguments[0],
             allowPotentiallyConstantType: false);
         valueType = buildDartType(typeArguments[1],
             allowPotentiallyConstantType: false);
         keyType = instantiateToBounds(
             keyType, coreTypes.objectClass, libraryBuilder.library);
         valueType = instantiateToBounds(
             valueType, coreTypes.objectClass, libraryBuilder.library);
       }
     } else {
       DartType implicitTypeArgument = this.implicitTypeArgument;
       keyType = implicitTypeArgument;
       valueType = implicitTypeArgument;
     }

     MapLiteral node = forest.createMapLiteral(
         // TODO(johnniwinther): The file offset computed below will not be
         // correct if there are type arguments but no `const` keyword.
         offsetForToken(constKeyword ?? leftBrace),
         keyType,
         valueType,
         entries,
         isConst: constKeyword != null ||
             constantContext == ConstantContext.inferred);
     libraryBuilder.checkBoundsInMapLiteral(node, typeEnvironment, uri);
     push(node);
   }

   @override
   void handleLiteralMapEntry(Token colon, Token endToken) {
     debugEvent("LiteralMapEntry");
     Expression value = popForValue();
     Expression key = popForValue();
     push(forest.createMapEntry(offsetForToken(colon), key, value));
   }

   String symbolPartToString(name) {
     if (name is Identifier) {
       return name.name;
     } else if (name is Operator) {
       return name.name;
     } else {
       return unhandled("${name.runtimeType}", "symbolPartToString", -1, uri);
     }
   }

   @override
   void endLiteralSymbol(Token hashToken, int identifierCount) {
     debugEvent("LiteralSymbol");
     if (identifierCount == 1) {
       Object? part = pop();
       if (part is ParserRecovery) {
         push(new ParserErrorGenerator(
             this, hashToken, fasta.messageSyntheticToken));
       } else {
         push(forest.createSymbolLiteral(
             offsetForToken(hashToken), symbolPartToString(part)));
       }
     } else {
       List<Identifier>? parts = const FixedNullableList<Identifier>()
           .popNonNullable(stack, identifierCount, dummyIdentifier);
       if (parts == null) {
         push(new ParserErrorGenerator(
             this, hashToken, fasta.messageSyntheticToken));
         return;
       }
       String value = symbolPartToString(parts.first);
       for (int i = 1; i < parts.length; i++) {
         value += ".${symbolPartToString(parts[i])}";
       }
       push(forest.createSymbolLiteral(offsetForToken(hashToken), value));
     }
   }

   @override
   void handleNonNullAssertExpression(Token bang) {
     assert(checkState(bang, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.Initializer,
         ValueKinds.ProblemBuilder
       ])
     ]));
     if (!libraryBuilder.isNonNullableByDefault) {
       reportNonNullAssertExpressionNotEnabled(bang);
     }
     Expression operand = popForValue();
     push(forest.createNullCheck(offsetForToken(bang), operand));
   }

   @override
   void handleType(Token beginToken, Token? questionMark) {
     // TODO(ahe): The scope is wrong for return types of generic functions.
     debugEvent("Type");
     if (!libraryBuilder.isNonNullableByDefault) {
       reportErrorIfNullableType(questionMark);
     }
     bool isMarkedAsNullable = questionMark != null;
     List<TypeBuilder>? arguments = pop() as List<TypeBuilder>?;
     Object? name = pop();
     if (name is QualifiedName) {
       QualifiedName qualified = name;
       Object prefix = qualified.qualifier;
       Token suffix = qualified.suffix;
       if (prefix is Generator) {
         name = prefix.qualifiedLookup(suffix);
       } else {
         String name = getNodeName(prefix);
         String displayName = debugName(name, suffix.lexeme);
         int offset = offsetForToken(beginToken);
         Message message = fasta.templateNotAType.withArguments(displayName);
         libraryBuilder.addProblem(
             message, offset, lengthOfSpan(beginToken, suffix), uri);
         push(new NamedTypeBuilder.fromTypeDeclarationBuilder(
             new InvalidTypeDeclarationBuilder(
                 name,
                 message.withLocation(
                     uri, offset, lengthOfSpan(beginToken, suffix))),
             libraryBuilder.nullableBuilderIfTrue(isMarkedAsNullable),
             fileUri: uri,
             charOffset: offset,
             instanceTypeVariableAccess:
                 InstanceTypeVariableAccessState.Unexpected));
         return;
       }
     }
     TypeBuilder? result;
     if (name is Generator) {
       bool allowPotentiallyConstantType;
       if (libraryBuilder.isNonNullableByDefault) {
         if (enableConstructorTearOffsInLibrary) {
           allowPotentiallyConstantType = true;
         } else {
           allowPotentiallyConstantType = inIsOrAsOperatorType;
         }
       } else {
         allowPotentiallyConstantType = false;
       }
       result = name.buildTypeWithResolvedArguments(
           libraryBuilder.nullableBuilderIfTrue(isMarkedAsNullable), arguments,
           allowPotentiallyConstantType: allowPotentiallyConstantType);
       // ignore: unnecessary_null_comparison
       if (result == null) {
         unhandled("null", "result", beginToken.charOffset, uri);
       }
     } else if (name is ProblemBuilder) {
       // TODO(ahe): Arguments could be passed here.
       libraryBuilder.addProblem(
           name.message, name.charOffset, name.name.length, name.fileUri);
       result = new NamedTypeBuilder.fromTypeDeclarationBuilder(
           new InvalidTypeDeclarationBuilder(
               name.name,
               name.message.withLocation(
                   name.fileUri, name.charOffset, name.name.length)),
           libraryBuilder.nullableBuilderIfTrue(isMarkedAsNullable),
           fileUri: name.fileUri,
           charOffset: name.charOffset,
           instanceTypeVariableAccess:
               InstanceTypeVariableAccessState.Unexpected);
     } else {
       unhandled(
           "${name.runtimeType}", "handleType", beginToken.charOffset, uri);
     }
     push(result);
   }

   @override
   void beginFunctionType(Token beginToken) {
     debugEvent("beginFunctionType");
   }

   void enterFunctionTypeScope(List<TypeVariableBuilder>? typeVariables) {
     debugEvent("enterFunctionTypeScope");
     enterLocalScope('FunctionTypeScope',
         scope.createNestedScope("function-type scope", isModifiable: true));
     if (typeVariables != null) {
       ScopeBuilder scopeBuilder = new ScopeBuilder(scope);
       for (TypeVariableBuilder builder in typeVariables) {
         String name = builder.name;
         TypeVariableBuilder? existing =
             scopeBuilder[name] as TypeVariableBuilder?;
         if (existing == null) {
           scopeBuilder.addMember(name, builder);
         } else {
           reportDuplicatedDeclaration(existing, name, builder.charOffset);
         }
       }
     }
   }

   @override
   void endFunctionType(Token functionToken, Token? questionMark) {
     debugEvent("FunctionType");
     if (!libraryBuilder.isNonNullableByDefault) {
       reportErrorIfNullableType(questionMark);
     }
     FormalParameters formals = pop() as FormalParameters;
     TypeBuilder? returnType = pop() as TypeBuilder?;
     List<TypeVariableBuilder>? typeVariables =
         pop() as List<TypeVariableBuilder>?;
     if (typeVariables != null) {
       for (TypeVariableBuilder builder in typeVariables) {
         if (builder.parameter.annotations.isNotEmpty) {
           if (!libraryBuilder.enableGenericMetadataInLibrary) {
             addProblem(fasta.messageAnnotationOnFunctionTypeTypeVariable,
                 builder.charOffset, builder.name.length);
           }
           // Annotations on function types are not constant evaluated and are
           // not included in the generated AST so we clear them here.
           builder.parameter.annotations = const <Expression>[];
         }
       }
     }
     TypeBuilder type = formals.toFunctionType(
         returnType,
         libraryBuilder.nullableBuilderIfTrue(questionMark != null),
         typeVariables);
     exitLocalScope();
     push(type);
   }

   @override
   void handleVoidKeyword(Token token) {
     debugEvent("VoidKeyword");
     int offset = offsetForToken(token);
     // "void" is always nullable.
     push(new NamedTypeBuilder.fromTypeDeclarationBuilder(
         new VoidTypeDeclarationBuilder(
             const VoidType(), libraryBuilder, offset),
         const NullabilityBuilder.nullable(),
         fileUri: uri,
         charOffset: offset,
         instanceTypeVariableAccess:
             InstanceTypeVariableAccessState.Unexpected));
   }

   @override
   void handleVoidKeywordWithTypeArguments(Token token) {
     assert(checkState(token, <ValueKind>[
       /* arguments */ ValueKinds.TypeArgumentsOrNull,
     ]));

     debugEvent("handleVoidKeywordWithTypeArguments");
     pop(); // arguments.
     handleVoidKeyword(token);
   }

   @override
   void beginAsOperatorType(Token operator) {
     _isOrAsOperatorTypeState = _isOrAsOperatorTypeState.prepend(true);
   }

   @override
   void endAsOperatorType(Token operator) {
     _isOrAsOperatorTypeState = _isOrAsOperatorTypeState.tail!;
   }

   @override
   void handleAsOperator(Token operator) {
     debugEvent("AsOperator");
     DartType type = buildDartType(pop() as TypeBuilder,
         allowPotentiallyConstantType: libraryBuilder.isNonNullableByDefault);
     libraryBuilder.checkBoundsInType(
         type, typeEnvironment, uri, operator.charOffset);
     Expression expression = popForValue();
     Expression asExpression = forest.createAsExpression(
         offsetForToken(operator), expression, type,
         forNonNullableByDefault: libraryBuilder.isNonNullableByDefault);
     push(asExpression);
   }

   @override
   void beginIsOperatorType(Token operator) {
     _isOrAsOperatorTypeState = _isOrAsOperatorTypeState.prepend(true);
   }

   @override
   void endIsOperatorType(Token operator) {
     _isOrAsOperatorTypeState = _isOrAsOperatorTypeState.tail!;
   }

   @override
   void handleIsOperator(Token isOperator, Token? not) {
     debugEvent("IsOperator");
     DartType type = buildDartType(pop() as TypeBuilder,
         allowPotentiallyConstantType: libraryBuilder.isNonNullableByDefault);
     Expression operand = popForValue();
     Expression isExpression = forest.createIsExpression(
         offsetForToken(isOperator), operand, type,
         forNonNullableByDefault: libraryBuilder.isNonNullableByDefault,
         notFileOffset: not != null ? offsetForToken(not) : null);
     libraryBuilder.checkBoundsInType(
         type, typeEnvironment, uri, isOperator.charOffset);
     push(isExpression);
   }

   @override
   void beginConditionalExpression(Token question) {
     Expression condition = popForValue();
     // This is matched by the call to [deferNode] in
     // [handleConditionalExpressionColon].
     typeInferrer.assignedVariables.beginNode();
     push(condition);
     super.beginConditionalExpression(question);
   }

   @override
   void handleConditionalExpressionColon() {
     Expression then = popForValue();
     // This is matched by the call to [beginNode] in
     // [beginConditionalExpression] and by the call to [storeInfo] in
     // [endConditionalExpression].
     push(typeInferrer.assignedVariables.deferNode());
     push(then);
     super.handleConditionalExpressionColon();
   }

   @override
   void endConditionalExpression(Token question, Token colon) {
     debugEvent("ConditionalExpression");
     Expression elseExpression = popForValue();
     Expression thenExpression = pop() as Expression;
     AssignedVariablesNodeInfo<VariableDeclaration> assignedVariablesInfo =
         pop() as AssignedVariablesNodeInfo<VariableDeclaration>;
     Expression condition = pop() as Expression;
     Expression node = forest.createConditionalExpression(
         offsetForToken(question), condition, thenExpression, elseExpression);
     push(node);
     // This is matched by the call to [deferNode] in
     // [handleConditionalExpressionColon].
     typeInferrer.assignedVariables.storeInfo(node, assignedVariablesInfo);
   }

   @override
   void handleThrowExpression(Token throwToken, Token endToken) {
     debugEvent("ThrowExpression");
     Expression expression = popForValue();
     if (constantContext != ConstantContext.none) {
       push(buildProblem(
           fasta.templateNotConstantExpression.withArguments('Throw'),
           throwToken.offset,
           throwToken.length));
     } else {
       push(forest.createThrow(offsetForToken(throwToken), expression));
     }
   }

   @override
   void beginFormalParameter(Token token, MemberKind kind, Token? requiredToken,
       Token? covariantToken, Token? varFinalOrConst) {
     // TODO(danrubel): handle required token
     if (!libraryBuilder.isNonNullableByDefault) {
       reportNonNullableModifierError(requiredToken);
     }
     push((covariantToken != null ? covariantMask : 0) |
         (requiredToken != null ? requiredMask : 0) |
         Modifier.validateVarFinalOrConst(varFinalOrConst?.lexeme));
   }

   @override
   void endFormalParameter(
       Token? thisKeyword,
       Token? superKeyword,
       Token? periodAfterThisOrSuper,
       Token nameToken,
       Token? initializerStart,
       Token? initializerEnd,
       FormalParameterKind kind,
       MemberKind memberKind) {
     debugEvent("FormalParameter");
     if (thisKeyword != null) {
       if (!inConstructor) {
         handleRecoverableError(fasta.messageFieldInitializerOutsideConstructor,
             thisKeyword, thisKeyword);
         thisKeyword = null;
       }
     }
     Object? nameNode = pop();
     TypeBuilder? type = pop() as TypeBuilder?;
     if (functionNestingLevel == 0 && type != null) {
       // TODO(ahe): The type we compute here may be different from what is
       // computed in the outline phase. We should make sure that the outline
       // phase computes the same type. See
       // pkg/front_end/testcases/deferred_type_annotation.dart for an example
       // where not calling [buildDartType] leads to a missing compile-time
       // error. Also, notice that the type of the problematic parameter isn't
       // `invalid-type`.
       buildDartType(type, allowPotentiallyConstantType: false);
     }
     int modifiers = pop() as int;
     if (inCatchClause) {
       modifiers |= finalMask;
     }
     List<Expression>? annotations = pop() as List<Expression>?;
     if (nameNode is ParserRecovery) {
       push(nameNode);
       return;
     }
     Identifier? name = nameNode as Identifier?;
     FormalParameterBuilder? parameter;
     if (!inCatchClause &&
         functionNestingLevel == 0 &&
         memberKind != MemberKind.GeneralizedFunctionType) {
       SourceFunctionBuilder member = this.member as SourceFunctionBuilder;
       parameter = member.getFormal(name!);
       if (parameter == null) {
         // This happens when the list of formals (originally) contains a
         // ParserRecovery - then the popped list becomes null.
         push(new ParserRecovery(nameToken.charOffset));
         return;
       }
     } else {
       parameter = new FormalParameterBuilder(null, modifiers, type,
           name?.name ?? '', libraryBuilder, offsetForToken(nameToken),
           fileUri: uri)
         ..hasDeclaredInitializer = (initializerStart != null);
     }
     VariableDeclaration variable =
         parameter.build(libraryBuilder, functionNestingLevel);
     Expression? initializer = name?.initializer;
     if (initializer != null) {
       if (member is RedirectingFactoryBuilder) {
         RedirectingFactoryBuilder factory = member as RedirectingFactoryBuilder;
         addProblem(
             fasta.templateDefaultValueInRedirectingFactoryConstructor
                 .withArguments(factory.redirectionTarget.fullNameForErrors),
             initializer.fileOffset,
             noLength);
       } else {
         if (!parameter.initializerWasInferred) {
           variable.initializer = initializer..parent = variable;
         }
       }
     } else if (kind != FormalParameterKind.mandatory) {
       variable.initializer ??= forest.createNullLiteral(noLocation)
         ..parent = variable;
     }
     if (annotations != null) {
       if (functionNestingLevel == 0) {
         inferAnnotations(variable, annotations);
       }
       variable.clearAnnotations();
       for (Expression annotation in annotations) {
         variable.addAnnotation(annotation);
       }
     }
     push(parameter);
     typeInferrer.assignedVariables.declare(variable);
   }

   @override
   void endOptionalFormalParameters(
       int count, Token beginToken, Token endToken) {
     debugEvent("OptionalFormalParameters");
     FormalParameterKind kind = optional("{", beginToken)
         ? FormalParameterKind.optionalNamed
         : FormalParameterKind.optionalPositional;
     // When recovering from an empty list of optional arguments, count may be
     // 0. It might be simpler if the parser didn't call this method in that
     // case, however, then [beginOptionalFormalParameters] wouldn't always be
     // matched by this method.
     List<FormalParameterBuilder>? parameters =
         const FixedNullableList<FormalParameterBuilder>()
             .popNonNullable(stack, count, dummyFormalParameterBuilder);
     if (parameters == null) {
       push(new ParserRecovery(offsetForToken(beginToken)));
     } else {
       for (FormalParameterBuilder parameter in parameters) {
         parameter.kind = kind;
       }
       push(parameters);
     }
   }

   @override
   void beginFunctionTypedFormalParameter(Token token) {
     debugEvent("beginFunctionTypedFormalParameter");
     functionNestingLevel++;
   }

   @override
   void endFunctionTypedFormalParameter(Token nameToken, Token? question) {
     debugEvent("FunctionTypedFormalParameter");
     if (inCatchClause || functionNestingLevel != 0) {
       exitLocalScope();
     }
     FormalParameters formals = pop() as FormalParameters;
     TypeBuilder? returnType = pop() as TypeBuilder?;
     List<TypeVariableBuilder>? typeVariables =
         pop() as List<TypeVariableBuilder>?;
     if (!libraryBuilder.isNonNullableByDefault) {
       reportErrorIfNullableType(question);
     }
     TypeBuilder type = formals.toFunctionType(returnType,
         libraryBuilder.nullableBuilderIfTrue(question != null), typeVariables);
     exitLocalScope();
     push(type);
     functionNestingLevel--;
   }

   @override
   void beginFormalParameterDefaultValueExpression() {
     super.push(constantContext);
     constantContext = ConstantContext.required;
   }

   @override
   void endFormalParameterDefaultValueExpression() {
     debugEvent("FormalParameterDefaultValueExpression");
     Object? defaultValueExpression = pop();
     constantContext = pop() as ConstantContext;
     push(defaultValueExpression);
   }

   @override
   void handleValuedFormalParameter(Token equals, Token token) {
     debugEvent("ValuedFormalParameter");
     Expression initializer = popForValue();
     Object? name = pop();
     if (name is ParserRecovery) {
       push(name);
     } else {
       push(new InitializedIdentifier(name as Identifier, initializer));
     }
   }

   @override
   void handleFormalParameterWithoutValue(Token token) {
     debugEvent("FormalParameterWithoutValue");
   }

   @override
   void beginFormalParameters(Token token, MemberKind kind) {
     super.push(constantContext);
     constantContext = ConstantContext.none;
   }

   @override
   void endFormalParameters(
       int count, Token beginToken, Token endToken, MemberKind kind) {
     debugEvent("FormalParameters");
     List<FormalParameterBuilder>? optionals;
     int optionalsCount = 0;
     if (count > 0 && peek() is List<FormalParameterBuilder>) {
       optionals = pop() as List<FormalParameterBuilder>;
       count--;
       optionalsCount = optionals.length;
     }
     List<FormalParameterBuilder>? parameters =
         const FixedNullableList<FormalParameterBuilder>().popPaddedNonNullable(
             stack, count, optionalsCount, dummyFormalParameterBuilder);
     if (optionals != null && parameters != null) {
       parameters.setRange(count, count + optionalsCount, optionals);
     }
     assert(parameters?.isNotEmpty ?? true);
     FormalParameters formals = new FormalParameters(parameters,
         offsetForToken(beginToken), lengthOfSpan(beginToken, endToken), uri);
     constantContext = pop() as ConstantContext;
     push(formals);
     if ((inCatchClause || functionNestingLevel != 0) &&
         kind != MemberKind.GeneralizedFunctionType) {
       enterLocalScope('formalParameters',
           formals.computeFormalParameterScope(scope, member, this));
     }
   }

   @override
   void beginCatchClause(Token token) {
     debugEvent("beginCatchClause");
     inCatchClause = true;
   }

   @override
   void endCatchClause(Token token) {
     debugEvent("CatchClause");
     inCatchClause = false;
     push(inCatchBlock);
     inCatchBlock = true;
   }

   @override
   void handleCatchBlock(Token? onKeyword, Token? catchKeyword, Token? comma) {
     debugEvent("CatchBlock");
     Statement body = pop() as Statement;
     inCatchBlock = pop() as bool;
     if (catchKeyword != null) {
       exitLocalScope();
     }
     FormalParameters? catchParameters =
         popIfNotNull(catchKeyword) as FormalParameters?;
     TypeBuilder? unresolvedExceptionType =
         popIfNotNull(onKeyword) as TypeBuilder?;
     DartType exceptionType;
     if (unresolvedExceptionType != null) {
       exceptionType = buildDartType(unresolvedExceptionType,
           allowPotentiallyConstantType: false);
     } else {
       exceptionType = (libraryBuilder.isNonNullableByDefault
           ? coreTypes.objectNonNullableRawType
           : const DynamicType());
     }
     FormalParameterBuilder? exception;
     FormalParameterBuilder? stackTrace;
     List<Statement>? compileTimeErrors;
     if (catchParameters?.parameters != null) {
       int parameterCount = catchParameters!.parameters!.length;
       if (parameterCount > 0) {
         exception = catchParameters.parameters![0];
         exception.build(libraryBuilder, functionNestingLevel).type =
             exceptionType;
         if (parameterCount > 1) {
           stackTrace = catchParameters.parameters![1];
           stackTrace.build(libraryBuilder, functionNestingLevel).type =
               coreTypes.stackTraceRawType(libraryBuilder.nonNullable);
         }
       }
       if (parameterCount > 2) {
         // If parameterCount is 0, the parser reported an error already.
         if (parameterCount != 0) {
           for (int i = 2; i < parameterCount; i++) {
             FormalParameterBuilder parameter = catchParameters.parameters![i];
             compileTimeErrors ??= <Statement>[];
             compileTimeErrors.add(buildProblemStatement(
                 fasta.messageCatchSyntaxExtraParameters, parameter.charOffset,
                 length: parameter.name.length));
           }
         }
       }
     }
     push(forest.createCatch(
         offsetForToken(onKeyword ?? catchKeyword),
         exceptionType,
         exception?.variable,
         stackTrace?.variable,
         coreTypes.stackTraceRawType(libraryBuilder.nonNullable),
         body));
     if (compileTimeErrors == null) {
       push(NullValue.Block);
     } else {
       push(forest.createBlock(noLocation, noLocation, compileTimeErrors));
     }
   }

   @override
   void beginTryStatement(Token token) {
     // This is matched by the call to [endNode] in [endTryStatement].
     typeInferrer.assignedVariables.beginNode();
   }

   @override
   void endTryStatement(
       int catchCount, Token tryKeyword, Token? finallyKeyword) {
     Statement? finallyBlock;
     if (finallyKeyword != null) {
       finallyBlock = pop() as Statement;
     } else {
       // This is matched by the call to [beginNode] in [beginTryStatement].
       tryStatementInfoStack = tryStatementInfoStack
           .prepend(typeInferrer.assignedVariables.deferNode());
     }
     List<Catch>? catchBlocks;
     List<Statement>? compileTimeErrors;
     if (catchCount != 0) {
       List<Object?> catchBlocksAndErrors =
           const FixedNullableList<Object?>().pop(stack, catchCount * 2)!;
       catchBlocks =
           new List<Catch>.filled(catchCount, dummyCatch, growable: true);
       for (int i = 0; i < catchCount; i++) {
         catchBlocks[i] = catchBlocksAndErrors[i * 2] as Catch;
         Statement? error = catchBlocksAndErrors[i * 2 + 1] as Statement?;
         if (error != null) {
           compileTimeErrors ??= <Statement>[];
           compileTimeErrors.add(error);
         }
       }
     }
     Statement tryBlock = popStatement();
     int fileOffset = offsetForToken(tryKeyword);
     Statement result = forest.createTryStatement(
         fileOffset, tryBlock, catchBlocks, finallyBlock);
     typeInferrer.assignedVariables
         .storeInfo(result, tryStatementInfoStack.head);
     tryStatementInfoStack = tryStatementInfoStack.tail!;

     if (compileTimeErrors != null) {
       compileTimeErrors.add(result);
       push(forest.createBlock(noLocation, noLocation, compileTimeErrors));
     } else {
       push(result);
     }
   }

   @override
   void handleIndexedExpression(
       Token? question, Token openSquareBracket, Token closeSquareBracket) {
     assert(checkState(openSquareBracket, [
       unionOfKinds([ValueKinds.Expression, ValueKinds.Generator]),
       unionOfKinds(
           [ValueKinds.Expression, ValueKinds.Generator, ValueKinds.Initializer])
     ]));
     debugEvent("IndexedExpression");
     Expression index = popForValue();
     Object? receiver = pop();
     bool isNullAware = question != null;
     if (isNullAware && !libraryBuilder.isNonNullableByDefault) {
       reportMissingNonNullableSupport(openSquareBracket);
     }
     if (receiver is Generator) {
       push(receiver.buildIndexedAccess(index, openSquareBracket,
           isNullAware: isNullAware));
     } else if (receiver is Expression) {
       push(IndexedAccessGenerator.make(this, openSquareBracket, receiver, index,
           isNullAware: isNullAware));
     } else {
       assert(receiver is Initializer);
       push(IndexedAccessGenerator.make(
           this, openSquareBracket, toValue(receiver), index,
           isNullAware: isNullAware));
     }
   }

   @override
   void handleUnaryPrefixExpression(Token token) {
     assert(checkState(token, <ValueKind>[
       unionOfKinds(<ValueKind>[
         ValueKinds.Expression,
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder
       ]),
     ]));
     debugEvent("UnaryPrefixExpression");
     Object? receiver = pop();
     if (optional("!", token)) {
       push(forest.createNot(offsetForToken(token), toValue(receiver)));
     } else {
       String operator = token.stringValue!;
       if (optional("-", token)) {
         operator = "unary-";
       }
       int fileOffset = offsetForToken(token);
       Name name = new Name(operator);
       if (receiver is Generator) {
         push(receiver.buildUnaryOperation(token, name));
       } else {
         assert(receiver is Expression);
         push(forest.createUnary(fileOffset, name, receiver as Expression));
       }
     }
   }

   Name incrementOperator(Token token) {
     if (optional("++", token)) return plusName;
     if (optional("--", token)) return minusName;
     return unhandled(token.lexeme, "incrementOperator", token.charOffset, uri);
   }

   @override
   void handleUnaryPrefixAssignmentExpression(Token token) {
     debugEvent("UnaryPrefixAssignmentExpression");
     Object? generator = pop();
     if (generator is Generator) {
       push(generator.buildPrefixIncrement(incrementOperator(token),
           offset: token.charOffset));
     } else {
       Expression value = toValue(generator);
       push(wrapInProblem(
           value, fasta.messageNotAnLvalue, value.fileOffset, noLength));
     }
   }

   @override
   void handleUnaryPostfixAssignmentExpression(Token token) {
     debugEvent("UnaryPostfixAssignmentExpression");
     Object? generator = pop();
     if (generator is Generator) {
       push(new DelayedPostfixIncrement(
           this, token, generator, incrementOperator(token)));
     } else {
       Expression value = toValue(generator);
       push(wrapInProblem(
           value, fasta.messageNotAnLvalue, value.fileOffset, noLength));
     }
   }

   @override
   void endConstructorReference(Token start, Token? periodBeforeName,
       Token endToken, ConstructorReferenceContext constructorReferenceContext) {
     debugEvent("ConstructorReference");
     pushQualifiedReference(
         start, periodBeforeName, constructorReferenceContext);
   }

   /// A qualified reference is something that matches one of:
   ///
   ///     identifier
   ///     identifier typeArguments? '.' identifier
   ///     identifier '.' identifier typeArguments? '.' identifier
   ///
   /// That is, one to three identifiers separated by periods and optionally one
   /// list of type arguments.
   ///
   /// A qualified reference can be used to represent both a reference to
   /// compile-time constant variable (metadata) or a constructor reference
   /// (used by metadata, new/const expression, and redirecting factories).
   ///
   /// Note that the parser will report errors if metadata includes type
   /// arguments, but will other preserve them for error recovery.
   ///
   /// A constructor reference can contain up to three identifiers:
   ///
   ///     a) type typeArguments?
   ///     b) type typeArguments? '.' name
   ///     c) prefix '.' type typeArguments?
   ///     d) prefix '.' type typeArguments? '.' name
   ///
   /// This isn't a legal constructor reference:
   ///
   ///     type '.' name typeArguments?
   ///
   /// But the parser can't tell this from type c) above.
   ///
   /// This method pops 2 (or 3 if `periodBeforeName != null`) values from the
   /// stack and pushes 3 values: a generator (the type in a constructor
   /// reference, or an expression in metadata), a list of type arguments, and a
   /// name.
   void pushQualifiedReference(Token start, Token? periodBeforeName,
       ConstructorReferenceContext constructorReferenceContext) {
     assert(checkState(start, [
       /*suffix*/ if (periodBeforeName != null)
         unionOfKinds([ValueKinds.Identifier, ValueKinds.ParserRecovery]),
       /*type arguments*/ ValueKinds.TypeArgumentsOrNull,
       /*type*/ unionOfKinds([
         ValueKinds.Generator,
         ValueKinds.QualifiedName,
         ValueKinds.ProblemBuilder,
         ValueKinds.ParserRecovery
       ]),
     ]));
     Object? suffixObject = popIfNotNull(periodBeforeName);
     Identifier? suffix;
     if (suffixObject is Identifier) {
       suffix = suffixObject;
     } else {
       assert(
           suffixObject == null || suffixObject is ParserRecovery,
           "Unexpected qualified name suffix $suffixObject "
           "(${suffixObject.runtimeType})");
       // There was a `.` without a suffix.
     }

     Identifier? identifier;
     List<TypeBuilder>? typeArguments = pop() as List<TypeBuilder>?;
     Object? type = pop();
     if (type is QualifiedName) {
       identifier = type;
       QualifiedName qualified = type;
       Object qualifier = qualified.qualifier;
       assert(checkValue(
           start,
           unionOfKinds([ValueKinds.Generator, ValueKinds.ProblemBuilder]),
           qualifier));
       if (qualifier is TypeUseGenerator && suffix == null) {
         type = qualifier;
         if (typeArguments != null) {
           // TODO(ahe): Point to the type arguments instead.
           addProblem(fasta.messageConstructorWithTypeArguments,
               identifier.charOffset, identifier.name.length);
         }
       } else if (qualifier is Generator) {
         if (constructorReferenceContext !=
             ConstructorReferenceContext.Implicit) {
           type = qualifier.qualifiedLookup(qualified.token);
         } else {
           type = qualifier.buildSelectorAccess(
               new PropertySelector(this, qualified.token,
                   new Name(qualified.name, libraryBuilder.nameOrigin)),
               qualified.token.charOffset,
               false);
         }
         identifier = null;
       } else if (qualifier is ProblemBuilder) {
         type = qualifier;
       } else {
         unhandled("${qualifier.runtimeType}", "pushQualifiedReference",
             start.charOffset, uri);
       }
     }
     String name;
     if (identifier != null && suffix != null) {
       name = "${identifier.name}.${suffix.name}";
     } else if (identifier != null) {
       name = identifier.name;
     } else if (suffix != null) {
       name = suffix.name;
     } else {
       name = "";
     }

     // TODO(johnniwinther): Provide sufficient offsets for pointing correctly
     //  to prefix, class name and suffix.
     push(type);
     push(typeArguments ?? NullValue.TypeArguments);
     push(name);
     push(suffix ?? identifier ?? NullValue.Identifier);

     assert(checkState(start, [
       /*constructor name identifier*/ ValueKinds.IdentifierOrNull,
       /*constructor name*/ ValueKinds.Name,
       /*type arguments*/ ValueKinds.TypeArgumentsOrNull,
       /*class*/ unionOfKinds([
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
         ValueKinds.ParserRecovery,
         ValueKinds.Expression,
       ]),
     ]));
   }

   @override
   Expression buildStaticInvocation(Member target, Arguments arguments,
       {Constness constness: Constness.implicit,
       TypeAliasBuilder? typeAliasBuilder,
       int charOffset: -1,
       int charLength: noLength}) {
     // The argument checks for the initial target of redirecting factories
     // invocations are skipped in Dart 1.
     List<TypeParameter> typeParameters = target.function!.typeParameters;
     if (target is Constructor) {
       assert(!target.enclosingClass.isAbstract);
       typeParameters = target.enclosingClass.typeParameters;
     }
     LocatedMessage? argMessage = checkArgumentsForFunction(
         target.function!, arguments, charOffset, typeParameters);
     if (argMessage != null) {
       return buildUnresolvedError(forest.createNullLiteral(charOffset),
           target.name.text, arguments, charOffset,
           candidate: target, message: argMessage, kind: UnresolvedKind.Method);
     }

     bool isConst = constness == Constness.explicitConst ||
         constantContext != ConstantContext.none;
     if (target is Constructor) {
       if (constantContext == ConstantContext.required &&
           constness == Constness.implicit) {
         addProblem(fasta.messageMissingExplicitConst, charOffset, charLength);
       }
       if (isConst && !target.isConst) {
         return buildProblem(
             fasta.messageNonConstConstructor, charOffset, charLength);
       }
       ConstructorInvocation node;
       if (typeAliasBuilder == null) {
         node = new ConstructorInvocation(target, arguments, isConst: isConst)
           ..fileOffset = charOffset;
         libraryBuilder.checkBoundsInConstructorInvocation(
             node, typeEnvironment, uri);
       } else {
         TypeAliasedConstructorInvocation constructorInvocation =
             node = new TypeAliasedConstructorInvocation(
                 typeAliasBuilder, target, arguments,
                 isConst: isConst)
               ..fileOffset = charOffset;
         // No type arguments were passed, so we need not check bounds.
         assert(arguments.types.isEmpty);
         typeAliasedConstructorInvocations.add(constructorInvocation);
       }
       return node;
     } else {
       Procedure procedure = target as Procedure;
       if (procedure.isFactory) {
         if (constantContext == ConstantContext.required &&
             constness == Constness.implicit) {
           addProblem(fasta.messageMissingExplicitConst, charOffset, charLength);
         }
         if (isConst && !procedure.isConst) {
           return buildProblem(
               fasta.messageNonConstFactory, charOffset, charLength);
         }
         StaticInvocation node;
         if (typeAliasBuilder == null) {
           FactoryConstructorInvocation factoryInvocation =
               new FactoryConstructorInvocation(target, arguments,
                   isConst: isConst)
                 ..fileOffset = charOffset;
           libraryBuilder.checkBoundsInFactoryInvocation(
               factoryInvocation, typeEnvironment, uri,
               inferred: !hasExplicitTypeArguments(arguments));
           redirectingFactoryInvocations.add(factoryInvocation);
           node = factoryInvocation;
         } else {
           TypeAliasedFactoryInvocation constructorInvocation =
               new TypeAliasedFactoryInvocation(
                   typeAliasBuilder, target, arguments,
                   isConst: isConst)
                 ..fileOffset = charOffset;
           // No type arguments were passed, so we need not check bounds.
           assert(arguments.types.isEmpty);
           typeAliasedFactoryInvocations.add(constructorInvocation);
           node = constructorInvocation;
         }
         return node;
       } else {
         assert(constness == Constness.implicit);
         return new StaticInvocation(target, arguments, isConst: false)
           ..fileOffset = charOffset;
       }
     }
   }

   @override
   Expression buildExtensionMethodInvocation(
       int fileOffset, Procedure target, Arguments arguments,
       {required bool isTearOff}) {
     List<TypeParameter> typeParameters = target.function.typeParameters;
     LocatedMessage? argMessage = checkArgumentsForFunction(
         target.function, arguments, fileOffset, typeParameters,
         isExtensionMemberInvocation: true);
     if (argMessage != null) {
       return buildUnresolvedError(forest.createNullLiteral(fileOffset),
           target.name.text, arguments, fileOffset,
           candidate: target, message: argMessage, kind: UnresolvedKind.Method);
     }

     Expression node;
     if (isTearOff) {
       node = new ExtensionTearOff(target, arguments);
     } else {
       node = new StaticInvocation(target, arguments);
     }
     node.fileOffset = fileOffset;
     return node;
   }

   @override
   LocatedMessage? checkArgumentsForFunction(FunctionNode function,
       Arguments arguments, int offset, List<TypeParameter> typeParameters,
       {bool isExtensionMemberInvocation = false}) {
     int requiredPositionalParameterCountToReport =
         function.requiredParameterCount;
     int positionalParameterCountToReport = function.positionalParameters.length;
     int positionalArgumentCountToReport =
         forest.argumentsPositional(arguments).length;
     if (isExtensionMemberInvocation) {
       // Extension member invocations have additional synthetic parameter for
       // `this`.
       --requiredPositionalParameterCountToReport;
       --positionalParameterCountToReport;
       --positionalArgumentCountToReport;
     }
     if (forest.argumentsPositional(arguments).length <
         function.requiredParameterCount) {
       return fasta.templateTooFewArguments
           .withArguments(requiredPositionalParameterCountToReport,
               positionalArgumentCountToReport)
           .withLocation(uri, arguments.fileOffset, noLength);
     }
     if (forest.argumentsPositional(arguments).length >
         function.positionalParameters.length) {
       return fasta.templateTooManyArguments
           .withArguments(
               positionalParameterCountToReport, positionalArgumentCountToReport)
           .withLocation(uri, arguments.fileOffset, noLength);
     }
     List<NamedExpression> named = forest.argumentsNamed(arguments);
     if (named.isNotEmpty) {
       Set<String> parameterNames =
           new Set.from(function.namedParameters.map((a) => a.name));
       for (NamedExpression argument in named) {
         if (!parameterNames.contains(argument.name)) {
           return fasta.templateNoSuchNamedParameter
               .withArguments(argument.name)
               .withLocation(uri, argument.fileOffset, argument.name.length);
         }
       }
     }
     if (function.namedParameters.isNotEmpty) {
       if (libraryBuilder.isNonNullableByDefault) {
         Set<String> argumentNames = new Set.from(named.map((a) => a.name));
         for (VariableDeclaration parameter in function.namedParameters) {
           if (parameter.isRequired && !argumentNames.contains(parameter.name)) {
             return fasta.templateValueForRequiredParameterNotProvidedError
                 .withArguments(parameter.name!)
                 .withLocation(uri, arguments.fileOffset, fasta.noLength);
           }
         }
       }
     }

     List<DartType> types = forest.argumentsTypeArguments(arguments);
     if (typeParameters.length != types.length) {
       if (types.length == 0) {
         // Expected `typeParameters.length` type arguments, but none given, so
         // we use type inference.
       } else {
         // A wrong (non-zero) amount of type arguments given. That's an error.
         // TODO(jensj): Position should be on type arguments instead.
         return fasta.templateTypeArgumentMismatch
             .withArguments(typeParameters.length)
             .withLocation(uri, offset, noLength);
       }
     }

     return null;
   }

   @override
   LocatedMessage? checkArgumentsForType(
       FunctionType function, Arguments arguments, int offset,
       {bool isExtensionMemberInvocation = false}) {
     int requiredPositionalParameterCountToReport =
         function.requiredParameterCount;
     int positionalParameterCountToReport = function.positionalParameters.length;
     int positionalArgumentCountToReport =
         forest.argumentsPositional(arguments).length;
     if (isExtensionMemberInvocation) {
       // Extension member invocations have additional synthetic parameter for
       // `this`.
       --requiredPositionalParameterCountToReport;
       --positionalParameterCountToReport;
       --positionalArgumentCountToReport;
     }
     if (forest.argumentsPositional(arguments).length <
         function.requiredParameterCount) {
       return fasta.templateTooFewArguments
           .withArguments(requiredPositionalParameterCountToReport,
               positionalArgumentCountToReport)
           .withLocation(uri, arguments.fileOffset, noLength);
     }
     if (forest.argumentsPositional(arguments).length >
         function.positionalParameters.length) {
       return fasta.templateTooManyArguments
           .withArguments(
               positionalParameterCountToReport, positionalArgumentCountToReport)
           .withLocation(uri, arguments.fileOffset, noLength);
     }
     List<NamedExpression> named = forest.argumentsNamed(arguments);
     if (named.isNotEmpty) {
       Set<String> names =
           new Set.from(function.namedParameters.map((a) => a.name));
       for (NamedExpression argument in named) {
         if (!names.contains(argument.name)) {
           return fasta.templateNoSuchNamedParameter
               .withArguments(argument.name)
               .withLocation(uri, argument.fileOffset, argument.name.length);
         }
       }
     }
     if (function.namedParameters.isNotEmpty) {
       if (libraryBuilder.isNonNullableByDefault) {
         Set<String> argumentNames = new Set.from(named.map((a) => a.name));
         for (NamedType parameter in function.namedParameters) {
           if (parameter.isRequired && !argumentNames.contains(parameter.name)) {
             return fasta.templateValueForRequiredParameterNotProvidedError
                 .withArguments(parameter.name)
                 .withLocation(uri, arguments.fileOffset, fasta.noLength);
           }
         }
       }
     }
     List<Object> types = forest.argumentsTypeArguments(arguments);
     List<TypeParameter> typeParameters = function.typeParameters;
     if (typeParameters.length != types.length && types.length != 0) {
       // A wrong (non-zero) amount of type arguments given. That's an error.
       // TODO(jensj): Position should be on type arguments instead.
       return fasta.templateTypeArgumentMismatch
           .withArguments(typeParameters.length)
           .withLocation(uri, offset, noLength);
     }

     return null;
   }

   @override
   void beginNewExpression(Token token) {
     debugEvent("beginNewExpression");
     super.push(constantContext);
     if (constantContext != ConstantContext.none) {
       addProblem(
           fasta.templateNotConstantExpression.withArguments('New expression'),
           token.charOffset,
           token.length);
     }
     constantContext = ConstantContext.none;
   }

   @override
   void beginConstExpression(Token token) {
     debugEvent("beginConstExpression");
     super.push(constantContext);
     constantContext = ConstantContext.inferred;
   }

   @override
   void beginConstLiteral(Token token) {
     debugEvent("beginConstLiteral");
     super.push(constantContext);
     constantContext = ConstantContext.inferred;
   }

   @override
   void beginImplicitCreationExpression(Token token) {
     debugEvent("beginImplicitCreationExpression");
     super.push(constantContext);
   }

   @override
   void endConstLiteral(Token token) {
     debugEvent("endConstLiteral");
     Object? literal = pop();
     constantContext = pop() as ConstantContext;
     push(literal);
   }

   @override
   void endNewExpression(Token token) {
     debugEvent("NewExpression");
     _buildConstructorReferenceInvocation(
         token.next!, token.offset, Constness.explicitNew,
         inMetadata: false, inImplicitCreationContext: false);
   }

   void _buildConstructorReferenceInvocation(
       Token nameToken, int offset, Constness constness,
       {required bool inMetadata, required bool inImplicitCreationContext}) {
     assert(checkState(nameToken, [
       /*arguments*/ ValueKinds.Arguments,
       /*constructor name identifier*/ ValueKinds.IdentifierOrNull,
       /*constructor name*/ ValueKinds.Name,
       /*type arguments*/ ValueKinds.TypeArgumentsOrNull,
       /*class*/ unionOfKinds([
         ValueKinds.Generator,
         ValueKinds.ProblemBuilder,
         ValueKinds.ParserRecovery,
         ValueKinds.Expression,
       ]),
       /*previous constant context*/ ValueKinds.ConstantContext,
     ]));
     Arguments arguments = pop() as Arguments;
     Identifier? nameLastIdentifier = pop(NullValue.Identifier) as Identifier?;
     Token nameLastToken = nameLastIdentifier?.token ?? nameToken;
     String name = pop() as String;
     List<TypeBuilder>? typeArguments = pop() as List<TypeBuilder>?;
     if (inMetadata && typeArguments != null) {
       if (!libraryBuilder.enableGenericMetadataInLibrary) {
         handleRecoverableError(fasta.messageMetadataTypeArguments,
             nameLastToken.next!, nameLastToken.next!);
       }
     }

     Object? type = pop();

     ConstantContext savedConstantContext = pop() as ConstantContext;
     if (type is Generator) {
       push(type.invokeConstructor(
           typeArguments, name, arguments, nameToken, nameLastToken, constness,
           inImplicitCreationContext: inImplicitCreationContext));
     } else if (type is ParserRecovery) {
       push(new ParserErrorGenerator(
           this, nameToken, fasta.messageSyntheticToken));
     } else if (type is InvalidExpression) {
       push(type);
     } else if (type is Expression) {
       push(createInstantiationAndInvocation(
           () => type, typeArguments, name, name, arguments,
           instantiationOffset: offset,
           invocationOffset: nameLastToken.charOffset,
           inImplicitCreationContext: inImplicitCreationContext));
     } else {
       String? typeName;
       if (type is ProblemBuilder) {
         typeName = type.fullNameForErrors;
       }
       push(buildUnresolvedError(forest.createNullLiteral(offset),
           debugName(typeName!, name), arguments, nameToken.charOffset,
           kind: UnresolvedKind.Constructor));
     }
     constantContext = savedConstantContext;
     assert(checkState(nameToken, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
       ])
     ]));
   }

   @override
   Expression createInstantiationAndInvocation(
       Expression Function() receiverFunction,
       List<TypeBuilder>? typeArguments,
       String className,
       String constructorName,
       Arguments arguments,
       {required int instantiationOffset,
       required int invocationOffset,
       required bool inImplicitCreationContext}) {
     if (enableConstructorTearOffsInLibrary && inImplicitCreationContext) {
       Expression receiver = receiverFunction();
       if (typeArguments != null) {
         if (receiver is StaticTearOff &&
                 (receiver.target.isFactory ||
                     isTearOffLowering(receiver.target)) ||
             receiver is ConstructorTearOff ||
             receiver is RedirectingFactoryTearOff) {
           return buildProblem(fasta.messageConstructorTearOffWithTypeArguments,
               instantiationOffset, noLength);
         }
         receiver = forest.createInstantiation(
             instantiationOffset,
             receiver,
             buildDartTypeArguments(typeArguments,
                 allowPotentiallyConstantType: true));
       }
       return forest.createMethodInvocation(invocationOffset, receiver,
           new Name(constructorName, libraryBuilder.nameOrigin), arguments);
     } else {
       if (typeArguments != null) {
         assert(forest.argumentsTypeArguments(arguments).isEmpty);
         forest.argumentsSetTypeArguments(
             arguments,
             buildDartTypeArguments(typeArguments,
                 allowPotentiallyConstantType: false));
       }
       return buildUnresolvedError(
           forest.createNullLiteral(instantiationOffset),
           constructorNameForDiagnostics(constructorName, className: className),
           arguments,
           invocationOffset,
           kind: UnresolvedKind.Constructor);
     }
   }

   @override
   void endImplicitCreationExpression(Token token, Token openAngleBracket) {
     debugEvent("ImplicitCreationExpression");
     _buildConstructorReferenceInvocation(
         token, openAngleBracket.offset, Constness.implicit,
         inMetadata: false, inImplicitCreationContext: true);
   }

   @override
   Expression buildConstructorInvocation(
       TypeDeclarationBuilder? type,
       Token nameToken,
       Token nameLastToken,
       Arguments? arguments,
       String name,
       List<TypeBuilder>? typeArguments,
       int charOffset,
       Constness constness,
       {bool isTypeArgumentsInForest = false,
       TypeDeclarationBuilder? typeAliasBuilder,
       required UnresolvedKind unresolvedKind}) {
     if (arguments == null) {
       return buildProblem(fasta.messageMissingArgumentList,
           nameToken.charOffset, nameToken.length);
     }
     if (name.isNotEmpty && arguments.types.isNotEmpty) {
       // TODO(ahe): Point to the type arguments instead.
       addProblem(fasta.messageConstructorWithTypeArguments,
           nameToken.charOffset, nameToken.length);
     }

     String? errorName;
     LocatedMessage? message;

     if (type is TypeAliasBuilder) {
       errorName = debugName(type.name, name);
       TypeAliasBuilder aliasBuilder = type;
       int numberOfTypeParameters = aliasBuilder.typeVariablesCount;
       int numberOfTypeArguments = typeArguments?.length ?? 0;
       if (typeArguments != null &&
           numberOfTypeParameters != numberOfTypeArguments) {
         // TODO(eernst): Use position of type arguments, not nameToken.
         return evaluateArgumentsBefore(
             arguments,
             buildProblem(
                 fasta.templateTypeArgumentMismatch
                     .withArguments(numberOfTypeParameters),
                 charOffset,
                 noLength));
       }
       type = aliasBuilder.unaliasDeclaration(null,
           isUsedAsClass: true,
           usedAsClassCharOffset: nameToken.charOffset,
           usedAsClassFileUri: uri);
       List<TypeBuilder> typeArgumentBuilders = [];
       if (typeArguments != null) {
         for (TypeBuilder typeBuilder in typeArguments) {
           typeArgumentBuilders.add(typeBuilder);
         }
       } else {
         if (aliasBuilder.typeVariablesCount > 0) {
           // Raw generic type alias used for instance creation, needs inference.
           ClassBuilder classBuilder;
           if (type is ClassBuilder) {
             classBuilder = type;
           } else {
             if (type is InvalidTypeDeclarationBuilder) {
               LocatedMessage message = type.message;
               return evaluateArgumentsBefore(
                   arguments,
                   buildProblem(message.messageObject, nameToken.charOffset,
                       nameToken.lexeme.length));
             }

             return buildUnresolvedError(forest.createNullLiteral(charOffset),
                 errorName, arguments, nameLastToken.charOffset,
                 message: message, kind: UnresolvedKind.Constructor);
           }
           MemberBuilder? b = classBuilder.findConstructorOrFactory(
               name, charOffset, uri, libraryBuilder);
           Member? target = b?.member;
           if (b == null) {
             // Not found. Reported below.
           } else if (b is AmbiguousMemberBuilder) {
             message = b.message.withLocation(uri, charOffset, noLength);
           } else if (b.isConstructor) {
             if (classBuilder.isAbstract) {
               return evaluateArgumentsBefore(
                   arguments,
                   buildAbstractClassInstantiationError(
                       fasta.templateAbstractClassInstantiation
                           .withArguments(type.name),
                       type.name,
                       nameToken.charOffset));
             }
           }
           if (target is Constructor ||
               (target is Procedure && target.kind == ProcedureKind.Factory)) {
             Expression invocation;
             invocation = buildStaticInvocation(target!, arguments,
                 constness: constness,
                 typeAliasBuilder: aliasBuilder,
                 charOffset: nameToken.charOffset,
                 charLength: nameToken.length);
             return invocation;
           } else {
             return buildUnresolvedError(forest.createNullLiteral(charOffset),
                 errorName, arguments, nameLastToken.charOffset,
                 message: message, kind: UnresolvedKind.Constructor);
           }
         } else {
           // Empty `typeArguments` and `aliasBuilder``is non-generic, but it
           // may still unalias to a class type with some type arguments.
           if (type is ClassBuilder) {
             List<TypeBuilder>? unaliasedTypeArgumentBuilders =
                 aliasBuilder.unaliasTypeArguments(const []);
             if (unaliasedTypeArgumentBuilders == null) {
               // TODO(eernst): This is a wrong number of type arguments,
               // occurring indirectly (in an alias of an alias, etc.).
               return evaluateArgumentsBefore(
                   arguments,
                   buildProblem(
                       fasta.templateTypeArgumentMismatch
                           .withArguments(numberOfTypeParameters),
                       nameToken.charOffset,
                       nameToken.length,
                       suppressMessage: true));
             }
             List<DartType> dartTypeArguments = [];
             for (TypeBuilder typeBuilder in unaliasedTypeArgumentBuilders) {
               dartTypeArguments.add(typeBuilder.build(libraryBuilder));
             }
             assert(forest.argumentsTypeArguments(arguments).isEmpty);
             forest.argumentsSetTypeArguments(arguments, dartTypeArguments);
           }
         }
       }

       List<DartType> typeArgumentsToCheck = const <DartType>[];
       // ignore: unnecessary_null_comparison
       if (typeArgumentBuilders != null && typeArgumentBuilders.isNotEmpty) {
         typeArgumentsToCheck = new List.filled(
             typeArgumentBuilders.length, const DynamicType(),
             growable: false);
         for (int i = 0; i < typeArgumentsToCheck.length; ++i) {
           typeArgumentsToCheck[i] =
               typeArgumentBuilders[i].build(libraryBuilder);
         }
       }
       DartType typeToCheck = new TypedefType(
           aliasBuilder.typedef, Nullability.nonNullable, typeArgumentsToCheck);
       libraryBuilder.checkBoundsInType(
           typeToCheck, typeEnvironment, uri, charOffset,
           allowSuperBounded: false);

       if (type is ClassBuilder) {
         if (typeArguments != null) {
           int numberOfTypeParameters = aliasBuilder.typeVariables?.length ?? 0;
           if (numberOfTypeParameters != typeArgumentBuilders.length) {
             // TODO(eernst): Use position of type arguments, not nameToken.
             return evaluateArgumentsBefore(
                 arguments,
                 buildProblem(
                     fasta.templateTypeArgumentMismatch
                         .withArguments(numberOfTypeParameters),
                     nameToken.charOffset,
                     nameToken.length));
           }
           List<TypeBuilder>? unaliasedTypeArgumentBuilders =
               aliasBuilder.unaliasTypeArguments(typeArgumentBuilders);
           if (unaliasedTypeArgumentBuilders == null) {
             // TODO(eernst): This is a wrong number of type arguments,
             // occurring indirectly (in an alias of an alias, etc.).
             return evaluateArgumentsBefore(
                 arguments,
                 buildProblem(
                     fasta.templateTypeArgumentMismatch
                         .withArguments(numberOfTypeParameters),
                     nameToken.charOffset,
                     nameToken.length,
                     suppressMessage: true));
           }
           List<DartType> dartTypeArguments = [];
           for (TypeBuilder typeBuilder in unaliasedTypeArgumentBuilders) {
             dartTypeArguments.add(typeBuilder.build(libraryBuilder));
           }
           assert(forest.argumentsTypeArguments(arguments).isEmpty);
           forest.argumentsSetTypeArguments(arguments, dartTypeArguments);
         } else {
           ClassBuilder cls = type;
           if (cls.typeVariables?.isEmpty ?? true) {
             assert(forest.argumentsTypeArguments(arguments).isEmpty);
             forest.argumentsSetTypeArguments(arguments, []);
           } else {
             if (forest.argumentsTypeArguments(arguments).isEmpty) {
               // No type arguments provided to unaliased class, use defaults.
               List<DartType> result = new List<DartType>.generate(
                   cls.typeVariables!.length,
                   (int i) =>
                       cls.typeVariables![i].defaultType!.build(cls.library),
                   growable: true);
               forest.argumentsSetTypeArguments(arguments, result);
             }
           }
         }
       }
     } else {
       if (typeArguments != null && !isTypeArgumentsInForest) {
         assert(forest.argumentsTypeArguments(arguments).isEmpty);
         forest.argumentsSetTypeArguments(
             arguments,
             buildDartTypeArguments(typeArguments,
                 allowPotentiallyConstantType: false));
       }
     }
     if (type is ClassBuilder) {
       MemberBuilder? b =
           type.findConstructorOrFactory(name, charOffset, uri, libraryBuilder);
       Member? target;
       if (b == null) {
         // Not found. Reported below.
       } else if (b is AmbiguousMemberBuilder) {
         message = b.message.withLocation(uri, charOffset, noLength);
       } else if (b.isConstructor) {
         if (type.isAbstract) {
           return evaluateArgumentsBefore(
               arguments,
               buildAbstractClassInstantiationError(
                   fasta.templateAbstractClassInstantiation
                       .withArguments(type.name),
                   type.name,
                   nameToken.charOffset));
         }
         target = b.member;
       } else {
         target = b.member;
       }
       if (type is SourceEnumBuilder &&
           !(libraryBuilder.enableEnhancedEnumsInLibrary &&
               target is Procedure &&
               target.kind == ProcedureKind.Factory)) {
         return buildProblem(fasta.messageEnumInstantiation,
             nameToken.charOffset, nameToken.length);
       }
       if (target is Constructor ||
           (target is Procedure && target.kind == ProcedureKind.Factory)) {
         Expression invocation;

         invocation = buildStaticInvocation(target!, arguments,
             constness: constness,
             charOffset: nameToken.charOffset,
             charLength: nameToken.length,
             typeAliasBuilder: typeAliasBuilder as TypeAliasBuilder?);
         return invocation;
       } else {
         errorName ??= debugName(type.name, name);
       }
     } else if (type is InvalidTypeDeclarationBuilder) {
       LocatedMessage message = type.message;
       return evaluateArgumentsBefore(
           arguments,
           buildProblem(message.messageObject, nameToken.charOffset,
               nameToken.lexeme.length));
     } else {
       errorName ??= debugName(type!.fullNameForErrors, name);
     }

     return buildUnresolvedError(forest.createNullLiteral(charOffset), errorName,
         arguments, nameLastToken.charOffset,
         message: message, kind: unresolvedKind);
   }

   @override
   void endConstExpression(Token token) {
     debugEvent("endConstExpression");
     _buildConstructorReferenceInvocation(
         token.next!, token.offset, Constness.explicitConst,
         inMetadata: false, inImplicitCreationContext: false);
   }

   @override
   void handleConstFactory(Token constKeyword) {
     debugEvent("ConstFactory");
     if (!libraryBuilder.enableConstFunctionsInLibrary) {
       handleRecoverableError(
           fasta.messageConstFactory, constKeyword, constKeyword);
     }
   }

   @override
   void beginIfControlFlow(Token ifToken) {
     // TODO(danrubel): consider removing this when control flow support is added
     // if the ifToken is not needed for error reporting
     push(ifToken);
   }

   @override
   void handleThenControlFlow(Token token) {
     Expression condition = popForValue();
     // This is matched by the call to [deferNode] in
     // [handleElseControlFlow] and by the call to [endNode] in
     // [endIfControlFlow].
     typeInferrer.assignedVariables.beginNode();
     push(condition);
     super.handleThenControlFlow(token);
   }

   @override
   void handleElseControlFlow(Token elseToken) {
     // Resolve the top of the stack so that if it's a delayed assignment it
     // happens before we go into the else block.
     Object? node = pop();
     if (node is! MapLiteralEntry) node = toValue(node);
     // This is matched by the call to [beginNode] in
     // [handleThenControlFlow] and by the call to [storeInfo] in
     // [endIfElseControlFlow].
     push(typeInferrer.assignedVariables.deferNode());
     push(node);
   }

   @override
   void endIfControlFlow(Token token) {
     debugEvent("endIfControlFlow");
     Object? entry = pop();
     Object? condition = pop(); // parenthesized expression
     Token ifToken = pop() as Token;

     transformCollections = true;
     TreeNode node;
     if (entry is MapLiteralEntry) {
       node = forest.createIfMapEntry(
           offsetForToken(ifToken), toValue(condition), entry);
     } else {
       node = forest.createIfElement(
           offsetForToken(ifToken), toValue(condition), toValue(entry));
     }
     push(node);
     // This is matched by the call to [beginNode] in
     // [handleThenControlFlow].
     typeInferrer.assignedVariables.endNode(node);
   }

   @override
   void endIfElseControlFlow(Token token) {
     debugEvent("endIfElseControlFlow");
     Object? elseEntry = pop(); // else entry
     Object? thenEntry = pop(); // then entry
     AssignedVariablesNodeInfo<VariableDeclaration> assignedVariablesInfo =
         pop() as AssignedVariablesNodeInfo<VariableDeclaration>;
     Object? condition = pop(); // parenthesized expression
     Token ifToken = pop() as Token;

     transformCollections = true;
     TreeNode node;
     if (thenEntry is MapLiteralEntry) {
       if (elseEntry is MapLiteralEntry) {
         node = forest.createIfMapEntry(
             offsetForToken(ifToken), toValue(condition), thenEntry, elseEntry);
       } else if (elseEntry is ControlFlowElement) {
         MapLiteralEntry? elseMapEntry = elseEntry
             .toMapLiteralEntry(typeInferrer.assignedVariables.reassignInfo);
         if (elseMapEntry != null) {
           node = forest.createIfMapEntry(offsetForToken(ifToken),
               toValue(condition), thenEntry, elseMapEntry);
         } else {
           int offset = elseEntry.fileOffset;
           node = new MapLiteralEntry(
               buildProblem(
                   fasta.messageCantDisambiguateAmbiguousInformation, offset, 1),
               new NullLiteral())
             ..fileOffset = offsetForToken(ifToken);
         }
       } else {
         int offset = elseEntry is Expression
             ? elseEntry.fileOffset
             : offsetForToken(ifToken);
         node = new MapLiteralEntry(
             buildProblem(fasta.templateExpectedAfterButGot.withArguments(':'),
                 offset, 1),
             new NullLiteral())
           ..fileOffset = offsetForToken(ifToken);
       }
     } else if (elseEntry is MapLiteralEntry) {
       if (thenEntry is ControlFlowElement) {
         MapLiteralEntry? thenMapEntry = thenEntry
             .toMapLiteralEntry(typeInferrer.assignedVariables.reassignInfo);
         if (thenMapEntry != null) {
           node = forest.createIfMapEntry(offsetForToken(ifToken),
               toValue(condition), thenMapEntry, elseEntry);
         } else {
           int offset = thenEntry.fileOffset;
           node = new MapLiteralEntry(
               buildProblem(
                   fasta.messageCantDisambiguateAmbiguousInformation, offset, 1),
               new NullLiteral())
             ..fileOffset = offsetForToken(ifToken);
         }
       } else {
         int offset = thenEntry is Expression
             ? thenEntry.fileOffset
             : offsetForToken(ifToken);
         node = new MapLiteralEntry(
             buildProblem(fasta.templateExpectedAfterButGot.withArguments(':'),
                 offset, 1),
             new NullLiteral())
           ..fileOffset = offsetForToken(ifToken);
       }
     } else {
       node = forest.createIfElement(offsetForToken(ifToken), toValue(condition),
           toValue(thenEntry), toValue(elseEntry));
     }
     push(node);
     // This is matched by the call to [deferNode] in
     // [handleElseControlFlow].
     typeInferrer.assignedVariables.storeInfo(node, assignedVariablesInfo);
   }

   @override
   void handleSpreadExpression(Token spreadToken) {
     debugEvent("SpreadExpression");
     Object? expression = pop();
     transformCollections = true;
     push(forest.createSpreadElement(
         offsetForToken(spreadToken), toValue(expression),
         isNullAware: spreadToken.lexeme == '...?'));
   }

   @override
   void endTypeArguments(int count, Token beginToken, Token endToken) {
     debugEvent("TypeArguments");
     push(const FixedNullableList<TypeBuilder>()
             .popNonNullable(stack, count, dummyTypeBuilder) ??
         NullValue.TypeArguments);
   }

   @override
   void handleInvalidTypeArguments(Token token) {
     debugEvent("InvalidTypeArguments");
     pop(NullValue.TypeArguments);
   }

   @override
   void handleThisExpression(Token token, IdentifierContext context) {
     debugEvent("ThisExpression");
     if (context.isScopeReference && isDeclarationInstanceContext) {
       if (extensionThis != null) {
         push(_createReadOnlyVariableAccess(extensionThis!, token,
             offsetForToken(token), 'this', ReadOnlyAccessKind.ExtensionThis));
       } else {
         push(new ThisAccessGenerator(this, token, inInitializerLeftHandSide,
             inFieldInitializer, inLateFieldInitializer));
       }
     } else {
       push(new IncompleteErrorGenerator(
           this, token, fasta.messageThisAsIdentifier));
     }
   }

   @override
   void handleSuperExpression(Token token, IdentifierContext context) {
     debugEvent("SuperExpression");
     if (context.isScopeReference &&
         isDeclarationInstanceContext &&
         extensionThis == null) {
       MemberBuilder memberBuilder = member as MemberBuilder;
       memberBuilder.member.transformerFlags |= TransformerFlag.superCalls;
       push(new ThisAccessGenerator(this, token, inInitializerLeftHandSide,
           inFieldInitializer, inLateFieldInitializer,
           isSuper: true));
     } else {
       push(new IncompleteErrorGenerator(
           this, token, fasta.messageSuperAsIdentifier));
     }
   }

   @override
   void handleNamedArgument(Token colon) {
     debugEvent("NamedArgument");
     assert(checkState(colon, [
       unionOfKinds([
         ValueKinds.Expression,
         ValueKinds.Generator,
       ]),
       unionOfKinds([
         ValueKinds.Identifier,
         ValueKinds.ParserRecovery,
       ])
     ]));
     Expression value = popForValue();
     Object? identifier = pop();
     if (identifier is Identifier) {
       push(new NamedExpression(identifier.name, value)
         ..fileOffset = identifier.charOffset);
     } else {
       assert(
           identifier is ParserRecovery,
           "Unexpected argument name: "
           "${identifier} (${identifier.runtimeType})");
       push(identifier);
     }
   }

   @override
   void endFunctionName(Token beginToken, Token token) {
     debugEvent("FunctionName");
     Identifier name = pop() as Identifier;
     Token nameToken = name.token;
     VariableDeclaration variable = new VariableDeclarationImpl(
         name.name, functionNestingLevel,
         forSyntheticToken: nameToken.isSynthetic,
         isFinal: true,
         isLocalFunction: true)
       ..fileOffset = name.charOffset;
     // TODO(ahe): Why are we looking up in local scope, but declaring in parent
     // scope?
     Builder? existing = scope.lookupLocalMember(name.name, setter: false);
     if (existing != null) {
       reportDuplicatedDeclaration(existing, name.name, name.charOffset);
     }
     push(new FunctionDeclarationImpl(
         variable,
         // The real function node is created later.
         dummyFunctionNode)
       ..fileOffset = beginToken.charOffset);
     declareVariable(variable, scope.parent!);
   }

   void enterFunction() {
     _enterLocalState();
     debugEvent("enterFunction");
     functionNestingLevel++;
     push(switchScope ?? NullValue.SwitchScope);
     switchScope = null;
     push(inCatchBlock);
     inCatchBlock = false;
     // This is matched by the call to [endNode] in [pushNamedFunction] or
     // [endFunctionExpression].
     typeInferrer.assignedVariables.beginNode();
     assert(checkState(null, [
       /* inCatchBlock */ ValueKinds.Bool,
       /* switch scope */ ValueKinds.SwitchScopeOrNull,
     ]));
   }

   void exitFunction() {
     assert(checkState(null, [
       /* inCatchBlock */ ValueKinds.Bool,
       /* switch scope */ ValueKinds.SwitchScopeOrNull,
       /* function type variables */ ValueKinds.TypeVariableListOrNull,
       /* function block scope */ ValueKinds.Scope,
     ]));
     debugEvent("exitFunction");
     functionNestingLevel--;
     inCatchBlock = pop() as bool;
     switchScope = pop() as Scope?;
     List<TypeVariableBuilder>? typeVariables =
         pop() as List<TypeVariableBuilder>?;
     exitLocalScope();
     push(typeVariables ?? NullValue.TypeVariables);
     _exitLocalState();
     assert(checkState(null, [
       ValueKinds.TypeVariableListOrNull,
     ]));
   }

   @override
   void beginLocalFunctionDeclaration(Token token) {
     debugEvent("beginLocalFunctionDeclaration");
     enterFunction();
   }

   @override
   void beginNamedFunctionExpression(Token token) {
     debugEvent("beginNamedFunctionExpression");
     List<TypeVariableBuilder>? typeVariables =
         pop() as List<TypeVariableBuilder>?;
     // Create an additional scope in which the named function expression is
     // declared.
     enterLocalScope("named function");
     push(typeVariables ?? NullValue.TypeVariables);
     enterFunction();
   }

   @override
   void beginFunctionExpression(Token token) {
     debugEvent("beginFunctionExpression");
     enterFunction();
   }

   void pushNamedFunction(Token token, bool isFunctionExpression) {
     Statement body = popStatement();
     AsyncMarker asyncModifier = pop() as AsyncMarker;
     exitLocalScope();
     FormalParameters formals = pop() as FormalParameters;
     Object? declaration = pop();
     TypeBuilder? returnType = pop() as TypeBuilder?;
     bool hasImplicitReturnType = returnType == null;
     exitFunction();
     List<TypeVariableBuilder>? typeParameters =
         pop() as List<TypeVariableBuilder>?;
     List<Expression>? annotations;
     if (!isFunctionExpression) {
       annotations = pop() as List<Expression>?; // Metadata.
     }
     FunctionNode function = formals.buildFunctionNode(libraryBuilder,
         returnType, typeParameters, asyncModifier, body, token.charOffset);

     if (declaration is FunctionDeclaration) {
       VariableDeclaration variable = declaration.variable;
       if (annotations != null) {
         for (Expression annotation in annotations) {
           variable.addAnnotation(annotation);
         }
       }
       FunctionDeclarationImpl.setHasImplicitReturnType(
           declaration as FunctionDeclarationImpl, hasImplicitReturnType);
       if (!hasImplicitReturnType) {
         checkAsyncReturnType(asyncModifier, function.returnType,
             variable.fileOffset, variable.name!.length);
       }

       variable.type = function.computeFunctionType(libraryBuilder.nonNullable);
       if (isFunctionExpression) {
         Expression? oldInitializer = variable.initializer;
         variable.initializer = new FunctionExpression(function)
           ..parent = variable
           ..fileOffset = formals.charOffset;
         exitLocalScope();
         // This is matched by the call to [beginNode] in [enterFunction].
         typeInferrer.assignedVariables.endNode(variable.initializer!,
             isClosureOrLateVariableInitializer: true);
         Expression expression = new NamedFunctionExpressionJudgment(variable);
         if (oldInitializer != null) {
           // This must have been a compile-time error.
           Expression error = oldInitializer;
           assert(isErroneousNode(error));
           int offset = expression.fileOffset;
           push(new Let(
               new VariableDeclaration.forValue(error)..fileOffset = offset,
               expression)
             ..fileOffset = offset);
         } else {
           push(expression);
         }
       } else {
         declaration.function = function;
         function.parent = declaration;
         if (variable.initializer != null) {
           // This must have been a compile-time error.
           assert(isErroneousNode(variable.initializer!));

           push(forest
               .createBlock(declaration.fileOffset, noLocation, <Statement>[
             forest.createExpressionStatement(
                 offsetForToken(token), variable.initializer!),
             declaration
           ]));
           variable.initializer = null;
         } else {
           push(declaration);
         }
         // This is matched by the call to [beginNode] in [enterFunction].
         typeInferrer.assignedVariables
             .endNode(declaration, isClosureOrLateVariableInitializer: true);
       }
     } else {
       unhandled("${declaration.runtimeType}", "pushNamedFunction",
           token.charOffset, uri);
     }
   }

   @override
   void endNamedFunctionExpression(Token endToken) {
     debugEvent("NamedFunctionExpression");
     pushNamedFunction(endToken, true);
   }

   @override
   void endLocalFunctionDeclaration(Token token) {
     debugEvent("LocalFunctionDeclaration");
     pushNamedFunction(token, false);
   }

   @override
   void endFunctionExpression(Token beginToken, Token token) {
     debugEvent("FunctionExpression");
     assert(checkState(beginToken, [
       /* body */ ValueKinds.StatementOrNull,
       /* async marker */ ValueKinds.AsyncMarker,
       /* function type scope */ ValueKinds.Scope,
       /* formal parameters */ ValueKinds.FormalParameters,
       /* inCatchBlock */ ValueKinds.Bool,
       /* switch scope */ ValueKinds.SwitchScopeOrNull,
       /* function type variables */ ValueKinds.TypeVariableListOrNull,
       /* function block scope */ ValueKinds.Scope,
     ]));
     Statement body = popNullableStatement() ??
         // In erroneous cases, there might not be function body. In such cases
         // we use an empty statement instead.
         forest.createEmptyStatement(token.charOffset);
     AsyncMarker asyncModifier = pop() as AsyncMarker;
     exitLocalScope();
     FormalParameters formals = pop() as FormalParameters;
     exitFunction();
     List<TypeVariableBuilder>? typeParameters =
         pop() as List<TypeVariableBuilder>?;
     FunctionNode function = formals.buildFunctionNode(libraryBuilder, null,
         typeParameters, asyncModifier, body, token.charOffset)
       ..fileOffset = beginToken.charOffset;

     Expression result;
     if (constantContext != ConstantContext.none) {
       result = buildProblem(fasta.messageNotAConstantExpression,
           formals.charOffset, formals.length);
     } else {
       result = new FunctionExpression(function)
         ..fileOffset = offsetForToken(beginToken);
     }
     push(result);
     // This is matched by the call to [beginNode] in [enterFunction].
     typeInferrer.assignedVariables
         .endNode(result, isClosureOrLateVariableInitializer: true);
     assert(checkState(beginToken, [
       /* function expression or problem */ ValueKinds.Expression,
     ]));
   }

   @override
   void beginDoWhileStatement(Token token) {
     // This is matched by the [endNode] call in [endDoWhileStatement].
     typeInferrer.assignedVariables.beginNode();
     super.beginDoWhileStatement(token);
   }

   @override
   void endDoWhileStatement(
       Token doKeyword, Token whileKeyword, Token endToken) {
     debugEvent("DoWhileStatement");
     Expression condition = popForValue();
     Statement body = popStatement();
     JumpTarget continueTarget = exitContinueTarget()!;
     JumpTarget breakTarget = exitBreakTarget()!;
     List<BreakStatementImpl>? continueStatements;
     if (continueTarget.hasUsers) {
       LabeledStatement labeledStatement = forest.createLabeledStatement(body);
       continueStatements =
           continueTarget.resolveContinues(forest, labeledStatement);
       body = labeledStatement;
     }
     Statement doStatement =
         forest.createDoStatement(offsetForToken(doKeyword), body, condition);
     // This is matched by the [beginNode] call in [beginDoWhileStatement].
     typeInferrer.assignedVariables.endNode(doStatement);
     if (continueStatements != null) {
       for (BreakStatementImpl continueStatement in continueStatements) {
         continueStatement.targetStatement = doStatement;
       }
     }
     Statement result = doStatement;
     if (breakTarget.hasUsers) {
       LabeledStatement labeledStatement = forest.createLabeledStatement(result);
       breakTarget.resolveBreaks(forest, labeledStatement, doStatement);
       result = labeledStatement;
     }
     exitLoopOrSwitch(result);
   }

   @override
   void beginForInExpression(Token token) {
     enterLocalScope('forIn', scope.parent);
   }

   @override
   void endForInExpression(Token token) {
     debugEvent("ForInExpression");
     Expression expression = popForValue();
     exitLocalScope();
     push(expression);
   }

   @override
   void handleForInLoopParts(Token? awaitToken, Token forToken,
       Token leftParenthesis, Token inKeyword) {
     push(awaitToken ?? NullValue.AwaitToken);
     push(forToken);
     push(inKeyword);
     // This is matched by the call to [deferNode] in [endForIn] or
     // [endForInControlFlow].
     typeInferrer.assignedVariables.beginNode();
   }

   @override
   void endForInControlFlow(Token token) {
     debugEvent("ForInControlFlow");
     Object? entry = pop();
     Token inToken = pop() as Token;
     Token forToken = pop() as Token;
     Token? awaitToken = pop(NullValue.AwaitToken) as Token?;

     if (constantContext != ConstantContext.none) {
       popForValue(); // Pop iterable
       pop(); // Pop lvalue
       exitLocalScope();
       typeInferrer.assignedVariables.discardNode();

       handleRecoverableError(
           fasta.templateCantUseControlFlowOrSpreadAsConstant
               .withArguments(forToken),
           forToken,
           forToken);
       push(invalidCollectionElement);
       return;
     }

     // This is matched by the call to [beginNode] in [handleForInLoopParts].
     AssignedVariablesNodeInfo<VariableDeclaration> assignedVariablesNodeInfo =
         typeInferrer.assignedVariables.popNode();

     Expression iterable = popForValue();
     Object? lvalue = pop(); // lvalue
     exitLocalScope();

     transformCollections = true;
     ForInElements elements =
         _computeForInElements(forToken, inToken, lvalue, null);
     typeInferrer.assignedVariables.pushNode(assignedVariablesNodeInfo);
     VariableDeclaration variable = elements.variable;
     Expression? problem = elements.expressionProblem;
     if (entry is MapLiteralEntry) {
       ForInMapEntry result = forest.createForInMapEntry(
           offsetForToken(forToken),
           variable,
           iterable,
           elements.syntheticAssignment,
           elements.expressionEffects,
           entry,
           problem,
           isAsync: awaitToken != null);
       typeInferrer.assignedVariables.endNode(result);
       push(result);
     } else {
       ForInElement result = forest.createForInElement(
           offsetForToken(forToken),
           variable,
           iterable,
           elements.syntheticAssignment,
           elements.expressionEffects,
           toValue(entry),
           problem,
           isAsync: awaitToken != null);
       typeInferrer.assignedVariables.endNode(result);
       push(result);
     }
   }

   ForInElements _computeForInElements(
       Token forToken, Token inToken, Object? lvalue, Statement? body) {
     ForInElements elements = new ForInElements();
     if (lvalue is VariableDeclaration) {
       // Late for-in variables are not supported. An error has already been
       // reported by the parser.
       lvalue.isLate = false;
       elements.explicitVariableDeclaration = lvalue;
       if (lvalue.isConst) {
         elements.expressionProblem = buildProblem(
             fasta.messageForInLoopWithConstVariable,
             lvalue.fileOffset,
             lvalue.name!.length);
       }
     } else {
       VariableDeclaration variable = elements.syntheticVariableDeclaration =
           forest.createVariableDeclaration(
               offsetForToken(forToken), null, functionNestingLevel,
               isFinal: true);
       if (lvalue is Generator) {
         /// We are in this case, where `lvalue` isn't a [VariableDeclaration]:
         ///
         ///     for (lvalue in expression) body
         ///
         /// This is normalized to:
         ///
         ///     for (final #t in expression) {
         ///       lvalue = #t;
         ///       body;
         ///     }
         elements.syntheticAssignment = lvalue.buildAssignment(
             new VariableGetImpl(variable, forNullGuardedAccess: false)
               ..fileOffset = inToken.offset,
             voidContext: true);
       } else {
         Message message = forest.isVariablesDeclaration(lvalue)
             ? fasta.messageForInLoopExactlyOneVariable
             : fasta.messageForInLoopNotAssignable;
         Token token = forToken.next!.next!;
         elements.expressionProblem =
             buildProblem(message, offsetForToken(token), lengthForToken(token));
         Statement effects;
         if (forest.isVariablesDeclaration(lvalue)) {
           effects = forest.createBlock(
               noLocation,
               noLocation,
               // New list because the declarations are not a growable list.
               new List<Statement>.from(
                   forest.variablesDeclarationExtractDeclarations(lvalue)));
         } else {
           effects = forest.createExpressionStatement(
               noLocation, lvalue as Expression);
         }
         elements.expressionEffects = combineStatements(
             forest.createExpressionStatement(
                 noLocation,
                 buildProblem(
                     message, offsetForToken(token), lengthForToken(token))),
             effects);
       }
     }
     return elements;
   }

   @override
   void endForIn(Token endToken) {
     debugEvent("ForIn");
     Statement body = popStatement();

     Token inKeyword = pop() as Token;
     Token forToken = pop() as Token;
     Token? awaitToken = pop(NullValue.AwaitToken) as Token?;

     // This is matched by the call to [beginNode] in [handleForInLoopParts].
     AssignedVariablesNodeInfo<VariableDeclaration> assignedVariablesNodeInfo =
         typeInferrer.assignedVariables.deferNode();

     Expression expression = popForValue();
     Object? lvalue = pop();
     exitLocalScope();
     JumpTarget continueTarget = exitContinueTarget()!;
     JumpTarget breakTarget = exitBreakTarget()!;
     List<BreakStatementImpl>? continueStatements;
     if (continueTarget.hasUsers) {
       LabeledStatement labeledStatement = forest.createLabeledStatement(body);
       continueStatements =
           continueTarget.resolveContinues(forest, labeledStatement);
       body = labeledStatement;
     }
     ForInElements elements =
         _computeForInElements(forToken, inKeyword, lvalue, body);
     VariableDeclaration variable = elements.variable;
     Expression? problem = elements.expressionProblem;
     Statement forInStatement;
     if (elements.explicitVariableDeclaration != null) {
       forInStatement = new ForInStatement(variable, expression, body,
           isAsync: awaitToken != null)
         ..fileOffset = awaitToken?.charOffset ?? forToken.charOffset
         ..bodyOffset = body.fileOffset; // TODO(ahe): Isn't this redundant?
     } else {
       forInStatement = new ForInStatementWithSynthesizedVariable(
           variable,
           expression,
           elements.syntheticAssignment,
           elements.expressionEffects,
           body,
           isAsync: awaitToken != null,
           hasProblem: problem != null)
         ..fileOffset = awaitToken?.charOffset ?? forToken.charOffset
         ..bodyOffset = body.fileOffset; // TODO(ahe): Isn't this redundant?
     }
     typeInferrer.assignedVariables
         .storeInfo(forInStatement, assignedVariablesNodeInfo);
     if (continueStatements != null) {
       for (BreakStatementImpl continueStatement in continueStatements) {
         continueStatement.targetStatement = forInStatement;
       }
     }
     Statement result = forInStatement;
     if (breakTarget.hasUsers) {
       LabeledStatement labeledStatement = forest.createLabeledStatement(result);
       breakTarget.resolveBreaks(forest, labeledStatement, forInStatement);
       result = labeledStatement;
     }
     if (problem != null) {
       result = combineStatements(
           forest.createExpressionStatement(noLocation, problem), result);
     }
     exitLoopOrSwitch(result);
   }

   @override
   void handleLabel(Token token) {
     debugEvent("Label");
     Identifier identifier = pop() as Identifier;
     push(new Label(identifier.name, identifier.charOffset));
   }

   @override
   void beginLabeledStatement(Token token, int labelCount) {
     debugEvent("beginLabeledStatement");
     List<Label>? labels = const FixedNullableList<Label>()
         .popNonNullable(stack, labelCount, dummyLabel);
     enterLocalScope('labeledStatement', scope.createNestedLabelScope());
     LabelTarget target = new LabelTarget(
         member as MemberBuilder, functionNestingLevel, token.charOffset);
     if (labels != null) {
       for (Label label in labels) {
         scope.declareLabel(label.name, target);
       }
     }
     push(target);
   }

   @override
   void endLabeledStatement(int labelCount) {
     debugEvent("LabeledStatement");
     Statement statement = pop() as Statement;
     LabelTarget target = pop() as LabelTarget;
     exitLocalScope();
     if (target.breakTarget.hasUsers || target.continueTarget.hasUsers) {
       if (forest.isVariablesDeclaration(statement)) {
         internalProblem(
             fasta.messageInternalProblemLabelUsageInVariablesDeclaration,
             statement.fileOffset,
             uri);
       }
       if (statement is! LabeledStatement) {
         statement = forest.createLabeledStatement(statement);
       }
       target.breakTarget.resolveBreaks(forest, statement, statement);
       List<BreakStatementImpl>? continueStatements =
           target.continueTarget.resolveContinues(forest, statement);
       if (continueStatements != null) {
         for (BreakStatementImpl continueStatement in continueStatements) {
           continueStatement.targetStatement = statement;
         }
       }
     }
     push(statement);
   }

   @override
   void endRethrowStatement(Token rethrowToken, Token endToken) {
     debugEvent("RethrowStatement");
     if (inCatchBlock) {
       push(forest.createRethrowStatement(
           offsetForToken(rethrowToken), offsetForToken(endToken)));
     } else {
       push(new ExpressionStatement(buildProblem(fasta.messageRethrowNotCatch,
           offsetForToken(rethrowToken), lengthForToken(rethrowToken)))
         ..fileOffset = offsetForToken(rethrowToken));
     }
   }

   @override
   void handleFinallyBlock(Token finallyKeyword) {
     debugEvent("FinallyBlock");
     // Do nothing, handled by [endTryStatement].
   }

   @override
   void beginWhileStatement(Token token) {
     // This is matched by the [endNode] call in [endWhileStatement].
     typeInferrer.assignedVariables.beginNode();
     super.beginWhileStatement(token);
   }

   @override
   void endWhileStatement(Token whileKeyword, Token endToken) {
     debugEvent("WhileStatement");
     Statement body = popStatement();
     Expression condition = popForValue();
     JumpTarget continueTarget = exitContinueTarget()!;
     JumpTarget breakTarget = exitBreakTarget()!;
     List<BreakStatementImpl>? continueStatements;
     if (continueTarget.hasUsers) {
       LabeledStatement labeledStatement = forest.createLabeledStatement(body);
       continueStatements =
           continueTarget.resolveContinues(forest, labeledStatement);
       body = labeledStatement;
     }
     Statement whileStatement = forest.createWhileStatement(
         offsetForToken(whileKeyword), condition, body);
     if (continueStatements != null) {
       for (BreakStatementImpl continueStatement in continueStatements) {
         continueStatement.targetStatement = whileStatement;
       }
     }
     Statement result = whileStatement;
     if (breakTarget.hasUsers) {
       LabeledStatement labeledStatement = forest.createLabeledStatement(result);
       breakTarget.resolveBreaks(forest, labeledStatement, whileStatement);
       result = labeledStatement;
     }
     exitLoopOrSwitch(result);
     // This is matched by the [beginNode] call in [beginWhileStatement].
     typeInferrer.assignedVariables.endNode(whileStatement);
   }

   @override
   void handleEmptyStatement(Token token) {
     debugEvent("EmptyStatement");
     push(forest.createEmptyStatement(offsetForToken(token)));
   }

   @override
   void beginAssert(Token assertKeyword, Assert kind) {
     debugEvent("beginAssert");
     // If in an assert initializer, make sure [inInitializer] is false so we
     // use the formal parameter scope. If this is any other kind of assert,
     // inInitializer should be false anyway.
     inInitializerLeftHandSide = false;
   }

   @override
   void endAssert(Token assertKeyword, Assert kind, Token leftParenthesis,
       Token? commaToken, Token semicolonToken) {
     debugEvent("Assert");
     Expression? message = popForValueIfNotNull(commaToken);
     Expression condition = popForValue();
     int fileOffset = offsetForToken(assertKeyword);

     /// Return a representation of an assert that appears as a statement.
     AssertStatement createAssertStatement() {
       // Compute start and end offsets for the condition expression.
       // This code is a temporary workaround because expressions don't carry
       // their start and end offsets currently.
       //
       // The token that follows leftParenthesis is considered to be the
       // first token of the condition.
       // TODO(ahe): this really should be condition.fileOffset.
       int startOffset = leftParenthesis.next!.offset;
       int endOffset;

       // Search forward from leftParenthesis to find the last token of
       // the condition - which is a token immediately followed by a commaToken,
       // right parenthesis or a trailing comma.
       Token? conditionBoundary = commaToken ?? leftParenthesis.endGroup;
       Token conditionLastToken = leftParenthesis;
       while (!conditionLastToken.isEof) {
         Token nextToken = conditionLastToken.next!;
         if (nextToken == conditionBoundary) {
           break;
         } else if (optional(',', nextToken) &&
             nextToken.next == conditionBoundary) {
           // The next token is trailing comma, which means current token is
           // the last token of the condition.
           break;
         }
         conditionLastToken = nextToken;
       }
       if (conditionLastToken.isEof) {
         endOffset = startOffset = -1;
       } else {
         endOffset = conditionLastToken.offset + conditionLastToken.length;
       }

       return forest.createAssertStatement(
           fileOffset, condition, message, startOffset, endOffset);
     }

     switch (kind) {
       case Assert.Statement:
         push(createAssertStatement());
         break;

       case Assert.Expression:
         // The parser has already reported an error indicating that assert
         // cannot be used in an expression.
         push(buildProblem(
             fasta.messageAssertAsExpression, fileOffset, assertKeyword.length));
         break;

       case Assert.Initializer:
         push(forest.createAssertInitializer(
             fileOffset, createAssertStatement()));
         break;
     }
   }

   @override
   void endYieldStatement(Token yieldToken, Token? starToken, Token endToken) {
     debugEvent("YieldStatement");
     push(forest.createYieldStatement(offsetForToken(yieldToken), popForValue(),
         isYieldStar: starToken != null));
   }

   @override
   void beginSwitchBlock(Token token) {
     debugEvent("beginSwitchBlock");
     // This is matched by the [endNode] call in [endSwitchStatement].
     typeInferrer.assignedVariables.beginNode();
     enterLocalScope("switch block");
     enterSwitchScope();
     enterBreakTarget(token.charOffset);
   }

   @override
   void beginSwitchCase(int labelCount, int expressionCount, Token firstToken) {
     debugEvent("beginSwitchCase");
     int count = labelCount + expressionCount;
     List<Object>? labelsAndExpressions = const FixedNullableList<Object>()
         .popNonNullable(stack, count, dummyLabel);
     List<Label>? labels =
         labelCount == 0 ? null : new List<Label>.filled(labelCount, dummyLabel);
     List<Expression> expressions = new List<Expression>.filled(
         expressionCount, dummyExpression,
         growable: true);
     int labelIndex = 0;
     int expressionIndex = 0;
     if (labelsAndExpressions != null) {
       for (Object labelOrExpression in labelsAndExpressions) {
         if (labelOrExpression is Label) {
           labels![labelIndex++] = labelOrExpression;
         } else {
           expressions[expressionIndex++] = labelOrExpression as Expression;
         }
       }
     }
     assert(scope == switchScope);
     if (labels != null) {
       for (Label label in labels) {
         String labelName = label.name;
         if (scope.hasLocalLabel(labelName)) {
           // TODO(ahe): Should validate this is a goto target.
           if (!scope.claimLabel(labelName)) {
             addProblem(
                 fasta.templateDuplicateLabelInSwitchStatement
                     .withArguments(labelName),
                 label.charOffset,
                 labelName.length);
           }
         } else {
           scope.declareLabel(
               labelName, createGotoTarget(firstToken.charOffset));
         }
       }
     }
     push(expressions);
     push(labels ?? NullValue.Labels);
     enterLocalScope("switch case");
   }

   @override
   void endSwitchCase(
       int labelCount,
       int expressionCount,
       Token? defaultKeyword,
       Token? colonAfterDefault,
       int statementCount,
       Token firstToken,
       Token endToken) {
     debugEvent("SwitchCase");
     // We always create a block here so that we later know that there's always
     // one synthetic block when we finish compiling the switch statement and
     // check this switch case to see if it falls through to the next case.
     Statement block = popBlock(statementCount, firstToken, null);
     exitLocalScope();
     List<Label>? labels = pop() as List<Label>?;
     List<Expression> expressions = pop() as List<Expression>;
     List<int> expressionOffsets = <int>[];
     for (Expression expression in expressions) {
       expressionOffsets.add(expression.fileOffset);
     }
     assert(labels == null || labels.isNotEmpty);
     push(new SwitchCaseImpl(expressions, expressionOffsets, block,
         isDefault: defaultKeyword != null, hasLabel: labels != null)
       ..fileOffset = firstToken.charOffset);
     push(labels ?? NullValue.Labels);
   }

   @override
   void endSwitchStatement(Token switchKeyword, Token endToken) {
     debugEvent("SwitchStatement");

     List<SwitchCase> cases = pop() as List<SwitchCase>;
     JumpTarget target = exitBreakTarget()!;
     exitSwitchScope();
     exitLocalScope();
     Expression expression = popForValue();
     Statement switchStatement = new SwitchStatement(expression, cases)
       ..fileOffset = switchKeyword.charOffset;
     Statement result = switchStatement;
     if (target.hasUsers) {
       LabeledStatement labeledStatement = forest.createLabeledStatement(result);
       target.resolveBreaks(forest, labeledStatement, switchStatement);
       result = labeledStatement;
     }
     exitLoopOrSwitch(result);
     // This is matched by the [beginNode] call in [beginSwitchBlock].
     typeInferrer.assignedVariables.endNode(switchStatement);
   }

   @override
   void endSwitchBlock(int caseCount, Token beginToken, Token endToken) {
     debugEvent("SwitchBlock");
     List<SwitchCase> cases =
         new List<SwitchCase>.filled(caseCount, dummySwitchCase, growable: true);
     for (int i = caseCount - 1; i >= 0; i--) {
       List<Label>? labels = pop() as List<Label>?;
       SwitchCase current = cases[i] = pop() as SwitchCase;
       if (labels != null) {
         for (Label label in labels) {
           JumpTarget? target =
               switchScope!.lookupLabel(label.name) as JumpTarget?;
           if (target != null) {
             target.resolveGotos(forest, current);
           }
         }
       }
     }
     for (int i = 0; i < caseCount - 1; i++) {
       SwitchCase current = cases[i];
       Block block = current.body as Block;
       // [block] is a synthetic block that is added to handle variable
       // declarations in the switch case.
       TreeNode? lastNode =
           block.statements.isEmpty ? null : block.statements.last;
       if (lastNode is Block) {
         // This is a non-synthetic block.
         Block block = lastNode;
         lastNode = block.statements.isEmpty ? null : block.statements.last;
       }
       if (lastNode is ExpressionStatement) {
         ExpressionStatement statement = lastNode;
         lastNode = statement.expression;
       }
       // The rule that every case block should end with one of the predefined
       // set of statements is specific to pre-NNBD code and is replaced with
       // another rule based on flow analysis for NNBD code.  For details, see
       // the following link:
       // https://github.com/dart-lang/language/blob/master/accepted/future-releases/nnbd/feature-specification.md#errors-and-warnings
       if (!libraryBuilder.isNonNullableByDefault) {
         if (lastNode is! BreakStatement &&
             lastNode is! ContinueSwitchStatement &&
             lastNode is! Rethrow &&
             lastNode is! ReturnStatement &&
             !forest.isThrow(lastNode)) {
           block.addStatement(new ExpressionStatement(
               buildFallThroughError(current.fileOffset)));
         }
       }
     }

     push(cases);
   }

   @override
   void handleCaseMatch(Token caseKeyword, Token colon) {
     debugEvent("CaseMatch");
     // Do nothing. Handled by [handleSwitchCase].
   }

   @override
   void handleBreakStatement(
       bool hasTarget, Token breakKeyword, Token endToken) {
     debugEvent("BreakStatement");
     JumpTarget? target = breakTarget;
     Identifier? identifier;
     String? name;
     if (hasTarget) {
       identifier = pop() as Identifier;
       name = identifier.name;
       target = scope.lookupLabel(name) as JumpTarget?;
     }
     if (target == null && name == null) {
       push(problemInLoopOrSwitch = buildProblemStatement(
           fasta.messageBreakOutsideOfLoop, breakKeyword.charOffset));
     } else if (target == null || !target.isBreakTarget) {
       Token labelToken = breakKeyword.next!;
       push(problemInLoopOrSwitch = buildProblemStatement(
           fasta.templateInvalidBreakTarget.withArguments(name!),
           labelToken.charOffset,
           length: labelToken.length));
     } else if (target.functionNestingLevel != functionNestingLevel) {
       push(buildProblemTargetOutsideLocalFunction(name, breakKeyword));
     } else {
       Statement statement =
           forest.createBreakStatement(offsetForToken(breakKeyword), identifier);
       target.addBreak(statement);
       push(statement);
     }
   }

   Statement buildProblemTargetOutsideLocalFunction(
       String? name, Token keyword) {
     Statement problem;
     bool isBreak = optional("break", keyword);
     if (name != null) {
       Template<Message Function(String)> template = isBreak
           ? fasta.templateBreakTargetOutsideFunction
           : fasta.templateContinueTargetOutsideFunction;
       problem = buildProblemStatement(
           template.withArguments(name), offsetForToken(keyword),
           length: lengthOfSpan(keyword, keyword.next));
     } else {
       Message message = isBreak
           ? fasta.messageAnonymousBreakTargetOutsideFunction
           : fasta.messageAnonymousContinueTargetOutsideFunction;
       problem = buildProblemStatement(message, offsetForToken(keyword),
           length: lengthForToken(keyword));
     }
     problemInLoopOrSwitch ??= problem;
     return problem;
   }

   @override
   void handleContinueStatement(
       bool hasTarget, Token continueKeyword, Token endToken) {
     debugEvent("ContinueStatement");
     JumpTarget? target = continueTarget;
     Identifier? identifier;
     String? name;
     if (hasTarget) {
       identifier = pop() as Identifier;
       name = identifier.name;
       Builder? namedTarget = scope.lookupLabel(identifier.name);
       if (namedTarget != null && namedTarget is! JumpTarget) {
         Token labelToken = continueKeyword.next!;
         push(problemInLoopOrSwitch = buildProblemStatement(
             fasta.messageContinueLabelNotTarget, labelToken.charOffset,
             length: labelToken.length));
         return;
       }
       target = namedTarget as JumpTarget?;
       if (target == null) {
         if (switchScope == null) {
           push(buildProblemStatement(
               fasta.templateLabelNotFound.withArguments(name),
               continueKeyword.next!.charOffset));
           return;
         }
         switchScope!.forwardDeclareLabel(
             identifier.name, target = createGotoTarget(identifier.charOffset));
       }
       if (target.isGotoTarget &&
           target.functionNestingLevel == functionNestingLevel) {
         ContinueSwitchStatement statement =
             new ContinueSwitchStatement(dummySwitchCase)
               ..fileOffset = continueKeyword.charOffset;
         target.addGoto(statement);
         push(statement);
         return;
       }
     }
     if (target == null) {
       push(problemInLoopOrSwitch = buildProblemStatement(
           fasta.messageContinueWithoutLabelInCase, continueKeyword.charOffset,
           length: continueKeyword.length));
     } else if (!target.isContinueTarget) {
       Token labelToken = continueKeyword.next!;
       push(problemInLoopOrSwitch = buildProblemStatement(
           fasta.templateInvalidContinueTarget.withArguments(name!),
           labelToken.charOffset,
           length: labelToken.length));
     } else if (target.functionNestingLevel != functionNestingLevel) {
       push(buildProblemTargetOutsideLocalFunction(name, continueKeyword));
     } else {
       Statement statement = forest.createContinueStatement(
           offsetForToken(continueKeyword), identifier);
       target.addContinue(statement);
       push(statement);
     }
   }

   @override
   void beginTypeVariable(Token token) {
     debugEvent("beginTypeVariable");
     assert(checkState(token, [
       unionOfKinds([ValueKinds.Identifier, ValueKinds.ParserRecovery]),
       ValueKinds.AnnotationListOrNull,
     ]));
     Object? name = pop();
     List<Expression>? annotations = pop() as List<Expression>?;
     String? typeVariableName;
     int typeVariableCharOffset;
     if (name is Identifier) {
       typeVariableName = name.name;
       typeVariableCharOffset = name.charOffset;
     } else if (name is ParserRecovery) {
       typeVariableName = TypeVariableBuilder.noNameSentinel;
       typeVariableCharOffset = name.charOffset;
     } else {
       unhandled("${name.runtimeType}", "beginTypeVariable.name",
           token.charOffset, uri);
     }
     TypeVariableBuilder variable = new TypeVariableBuilder(
         typeVariableName, libraryBuilder, typeVariableCharOffset, uri);
     if (annotations != null) {
       inferAnnotations(variable.parameter, annotations);
       for (Expression annotation in annotations) {
         variable.parameter.addAnnotation(annotation);
       }
     }
     push(variable);
   }

   @override
   void handleTypeVariablesDefined(Token token, int count) {
     debugEvent("handleTypeVariablesDefined");
     assert(count > 0);
     List<TypeVariableBuilder>? typeVariables =
         const FixedNullableList<TypeVariableBuilder>()
             .popNonNullable(stack, count, dummyTypeVariableBuilder);
     enterFunctionTypeScope(typeVariables);
     push(typeVariables);
   }

   @override
   void endTypeVariable(
       Token token, int index, Token? extendsOrSuper, Token? variance) {
     debugEvent("TypeVariable");
     TypeBuilder? bound = pop() as TypeBuilder?;
     // Peek to leave type parameters on top of stack.
     List<TypeVariableBuilder> typeVariables =
         peek() as List<TypeVariableBuilder>;

     TypeVariableBuilder variable = typeVariables[index];
     variable.bound = bound;
     if (variance != null) {
       if (!libraryBuilder.enableVarianceInLibrary) {
         reportVarianceModifierNotEnabled(variance);
       }
       variable.variance = Variance.fromString(variance.lexeme);
     }
   }

   @override
   void endTypeVariables(Token beginToken, Token endToken) {
     debugEvent("TypeVariables");
     // Peek to leave type parameters on top of stack.
     List<TypeVariableBuilder> typeVariables =
         peek() as List<TypeVariableBuilder>;

     List<TypeBuilder> unboundTypes = [];
     List<TypeVariableBuilder> unboundTypeVariables = [];
     List<TypeBuilder> calculatedBounds = calculateBounds(
         typeVariables,
         libraryBuilder.loader.target.dynamicType,
         libraryBuilder.loader.target.nullType,
         libraryBuilder.loader.target.objectClassBuilder,
         unboundTypes: unboundTypes,
         unboundTypeVariables: unboundTypeVariables);
     assert(unboundTypes.isEmpty,
         "Found a type not bound to a declaration in BodyBuilder.");
     for (int i = 0; i < typeVariables.length; ++i) {
       typeVariables[i].defaultType = calculatedBounds[i];
       typeVariables[i].defaultType!.resolveIn(
           scope,
           typeVariables[i].charOffset,
           typeVariables[i].fileUri!,
           libraryBuilder);
       typeVariables[i].finish(
           libraryBuilder,
           libraryBuilder.loader.target.objectClassBuilder,
           libraryBuilder.loader.target.dynamicType);
     }
     for (int i = 0; i < unboundTypeVariables.length; ++i) {
       unboundTypeVariables[i].finish(
           libraryBuilder,
           libraryBuilder.loader.target.objectClassBuilder,
           libraryBuilder.loader.target.dynamicType);
     }
     libraryBuilder.processPendingNullabilities();
   }

   @override
   void handleNoTypeVariables(Token token) {
     debugEvent("NoTypeVariables");
     enterFunctionTypeScope(null);
     push(NullValue.TypeVariables);
   }

   List<TypeParameter>? typeVariableBuildersToKernel(
       List<TypeVariableBuilder>? typeVariableBuilders) {
     if (typeVariableBuilders == null) return null;
     return new List<TypeParameter>.generate(typeVariableBuilders.length,
         (int i) => typeVariableBuilders[i].parameter,
         growable: true);
   }

   @override
   void handleInvalidStatement(Token token, Message message) {
     Statement statement = pop() as Statement;
     push(new ExpressionStatement(
         buildProblem(message, statement.fileOffset, noLength)));
   }

   @override
   Expression buildProblem(Message message, int charOffset, int length,
       {List<LocatedMessage>? context,
       bool suppressMessage: false,
       Expression? expression}) {
     if (!suppressMessage) {
       addProblem(message, charOffset, length,
           wasHandled: true, context: context);
     }
     String text = libraryBuilder.loader.target.context
         .format(message.withLocation(uri, charOffset, length), Severity.error)
         .plain;
     return new InvalidExpression(text, expression)..fileOffset = charOffset;
   }

   @override
   Expression wrapInProblem(
       Expression expression, Message message, int fileOffset, int length,
       {List<LocatedMessage>? context}) {
     Severity severity = message.code.severity;
     if (severity == Severity.error) {
       return wrapInLocatedProblem(
           expression, message.withLocation(uri, fileOffset, length),
           context: context);
     } else {
       addProblem(message, fileOffset, length, context: context);
       return expression;
     }
   }

   @override
   Expression wrapInLocatedProblem(Expression expression, LocatedMessage message,
       {List<LocatedMessage>? context}) {
     // TODO(askesc): Produce explicit error expression wrapping the original.
     // See [issue 29717](https://github.com/dart-lang/sdk/issues/29717)
     int offset = expression.fileOffset;
     if (offset == -1) {
       offset = message.charOffset;
     }
     return buildProblem(
         message.messageObject, message.charOffset, message.length,
         context: context, expression: expression);
   }

   Expression buildFallThroughError(int charOffset) {
     addProblem(fasta.messageSwitchCaseFallThrough, charOffset, noLength);

     // TODO(ahe): The following doesn't make sense for the Analyzer. It should
     // be moved to [Forest] or conditional on `forest is Fangorn`.

     // TODO(ahe): Compute a LocatedMessage above instead?
     Location? location = messages.getLocationFromUri(uri, charOffset);

     return forest.createThrow(
         charOffset,
         buildStaticInvocation(
             libraryBuilder
                 .loader.coreTypes.fallThroughErrorUrlAndLineConstructor,
             forest.createArguments(noLocation, <Expression>[
               forest.createStringLiteral(
                   charOffset, "${location?.file ?? uri}"),
               forest.createIntLiteral(charOffset, location?.line ?? 0),
             ]),
             constness: Constness.explicitNew,
             charOffset: charOffset));
   }

   Expression buildAbstractClassInstantiationError(
       Message message, String className,
       [int charOffset = -1]) {
     addProblemErrorIfConst(message, charOffset, className.length);
     // TODO(ahe): The following doesn't make sense to Analyzer AST.
     MemberBuilder constructor =
         libraryBuilder.loader.getAbstractClassInstantiationError();
     Expression invocation = buildStaticInvocation(
         constructor.member,
         forest.createArguments(charOffset,
             <Expression>[forest.createStringLiteral(charOffset, className)]),
         constness: Constness.explicitNew,
         charOffset: charOffset);
     return forest.createThrow(charOffset, invocation);
   }

   Statement buildProblemStatement(Message message, int charOffset,
       {List<LocatedMessage>? context,
       int? length,
       bool suppressMessage: false}) {
     length ??= noLength;
     return new ExpressionStatement(buildProblem(message, charOffset, length,
         context: context, suppressMessage: suppressMessage));
   }

   Statement wrapInProblemStatement(Statement statement, Message message) {
     // TODO(askesc): Produce explicit error statement wrapping the original.
     // See [issue 29717](https://github.com/dart-lang/sdk/issues/29717)
     return buildProblemStatement(message, statement.fileOffset);
   }

   @override
   Initializer buildInvalidInitializer(Expression expression,
       [int charOffset = -1]) {
     needsImplicitSuperInitializer = false;
     return new ShadowInvalidInitializer(
         new VariableDeclaration.forValue(expression))
       ..fileOffset = charOffset;
   }

   Initializer buildDuplicatedInitializer(Field field, Expression value,
       String name, int offset, int previousInitializerOffset) {
     return new ShadowInvalidFieldInitializer(
         field,
         value,
         new VariableDeclaration.forValue(buildProblem(
             fasta.templateConstructorInitializeSameInstanceVariableSeveralTimes
                 .withArguments(name),
             offset,
             noLength)))
       ..fileOffset = offset;
   }

   /// Parameter [formalType] should only be passed in the special case of
   /// building a field initializer as a desugaring of an initializing formal
   /// parameter.  The spec says the following:
   ///
   /// "If an explicit type is attached to the initializing formal, that is its
   /// static type.  Otherwise, the type of an initializing formal named _id_ is
   /// _Tid_, where _Tid_ is the type of the instance variable named _id_ in the
   /// immediately enclosing class.  It is a static warning if the static type of
   /// _id_ is not a subtype of _Tid_."
   @override
   List<Initializer> buildFieldInitializer(String name, int fieldNameOffset,
       int assignmentOffset, Expression expression,
       {FormalParameterBuilder? formal}) {
     Builder? builder = declarationBuilder!.lookupLocalMember(name);
     if (builder?.next != null) {
       // Duplicated name, already reported.
       return <Initializer>[
         buildInvalidInitializer(
             buildProblem(
                 fasta.templateDuplicatedDeclarationUse.withArguments(name),
                 fieldNameOffset,
                 name.length),
             fieldNameOffset)
       ];
     } else if (builder is SourceFieldBuilder &&
         builder.isDeclarationInstanceMember) {
       initializedFields ??= <String, int>{};
       if (initializedFields!.containsKey(name)) {
         return <Initializer>[
           buildDuplicatedInitializer(builder.field, expression, name,
               assignmentOffset, initializedFields![name]!)
         ];
       }
       initializedFields![name] = assignmentOffset;
       if (builder.isAbstract) {
         return <Initializer>[
           buildInvalidInitializer(
               buildProblem(fasta.messageAbstractFieldConstructorInitializer,
                   fieldNameOffset, name.length),
               fieldNameOffset)
         ];
       } else if (builder.isExternal) {
         return <Initializer>[
           buildInvalidInitializer(
               buildProblem(fasta.messageExternalFieldConstructorInitializer,
                   fieldNameOffset, name.length),
               fieldNameOffset)
         ];
       } else if (builder.isFinal && builder.hasInitializer) {
         addProblem(
             fasta.templateFieldAlreadyInitializedAtDeclaration
                 .withArguments(name),
             assignmentOffset,
             noLength,
             context: [
               fasta.templateFieldAlreadyInitializedAtDeclarationCause
                   .withArguments(name)
                   .withLocation(uri, builder.charOffset, name.length)
             ]);
         MemberBuilder constructor =
             libraryBuilder.loader.getDuplicatedFieldInitializerError();
         Expression invocation = buildStaticInvocation(
             constructor.member,
             forest.createArguments(assignmentOffset, <Expression>[
               forest.createStringLiteral(assignmentOffset, name)
             ]),
             constness: Constness.explicitNew,
             charOffset: assignmentOffset);
         return <Initializer>[
           new ShadowInvalidFieldInitializer(
               builder.field,
               expression,
               new VariableDeclaration.forValue(
                   forest.createThrow(assignmentOffset, invocation)))
             ..fileOffset = assignmentOffset
         ];
       } else {
         if (formal != null && formal.type != null) {
           DartType formalType = formal.variable!.type;
           if (!typeEnvironment.isSubtypeOf(formalType, builder.fieldType,
               SubtypeCheckMode.withNullabilities)) {
             libraryBuilder.addProblem(
                 fasta.templateInitializingFormalTypeMismatch.withArguments(
                     name,
                     formalType,
                     builder.fieldType,
                     libraryBuilder.isNonNullableByDefault),
                 assignmentOffset,
                 noLength,
                 uri,
                 context: [
                   fasta.messageInitializingFormalTypeMismatchField.withLocation(
                       builder.fileUri, builder.charOffset, noLength)
                 ]);
           }
         }
         DeclaredSourceConstructorBuilder constructorBuilder =
             member as DeclaredSourceConstructorBuilder;
         constructorBuilder.registerInitializedField(builder);
         return builder.buildInitializer(assignmentOffset, expression,
             isSynthetic: formal != null);
       }
     } else {
       return <Initializer>[
         buildInvalidInitializer(
             buildProblem(
                 fasta.templateInitializerForStaticField.withArguments(name),
                 fieldNameOffset,
                 name.length),
             fieldNameOffset)
       ];
     }
   }

   @override
   Initializer buildSuperInitializer(
       bool isSynthetic, Constructor constructor, Arguments arguments,
       [int charOffset = -1]) {
     if (member.isConst && !constructor.isConst) {
       addProblem(fasta.messageConstConstructorWithNonConstSuper, charOffset,
           constructor.name.text.length);
     }
     needsImplicitSuperInitializer = false;
     return new SuperInitializer(constructor, arguments)
       ..fileOffset = charOffset
       ..isSynthetic = isSynthetic;
   }

   @override
   Initializer buildRedirectingInitializer(
       Constructor constructor, Arguments arguments,
       [int charOffset = -1]) {
     if (classBuilder!
         .checkConstructorCyclic(member.name!, constructor.name.text)) {
       int length = constructor.name.text.length;
       if (length == 0) length = "this".length;
       addProblem(fasta.messageConstructorCyclic, charOffset, length);
       // TODO(askesc): Produce invalid initializer.
     }
     needsImplicitSuperInitializer = false;
     return new RedirectingInitializer(constructor, arguments)
       ..fileOffset = charOffset;
   }

   @override
   void handleOperator(Token token) {
     debugEvent("Operator");
     push(new Operator(token, token.charOffset));
   }

   @override
   void handleSymbolVoid(Token token) {
     debugEvent("SymbolVoid");
     push(new Identifier(token));
   }

   @override
   void handleInvalidFunctionBody(Token token) {
     if (member.isNative) {
       push(NullValue.FunctionBody);
     } else {
       push(forest.createBlock(offsetForToken(token), noLocation, <Statement>[
         buildProblemStatement(
             fasta.templateExpectedFunctionBody.withArguments(token),
             token.charOffset,
             length: token.length)
       ]));
     }
   }

   @override
   void handleTypeArgumentApplication(Token openAngleBracket) {
     assert(checkState(openAngleBracket, [
       ValueKinds.TypeArguments,
       unionOfKinds([ValueKinds.Generator, ValueKinds.Expression])
     ]));
     List<TypeBuilder>? typeArguments =
         pop() as List<TypeBuilder>?; // typeArguments
     if (libraryBuilder.enableConstructorTearOffsInLibrary) {
       Object? operand = pop();
       if (operand is Generator) {
         push(operand.applyTypeArguments(
             openAngleBracket.charOffset, typeArguments));
       } else if (operand is StaticTearOff &&
               (operand.target.isFactory || isTearOffLowering(operand.target)) ||
           operand is ConstructorTearOff ||
           operand is RedirectingFactoryTearOff) {
         push(buildProblem(fasta.messageConstructorTearOffWithTypeArguments,
             openAngleBracket.charOffset, noLength));
       } else {
         push(new Instantiation(
             toValue(operand),
             buildDartTypeArguments(typeArguments,
                 allowPotentiallyConstantType: true))
           ..fileOffset = openAngleBracket.charOffset);
       }
     } else {
       addProblem(
           templateExperimentNotEnabled.withArguments(
               'constructor-tearoffs',
               libraryBuilder.enableConstructorTearOffsVersionInLibrary
                   .toText()),
           openAngleBracket.charOffset,
           noLength);
     }
   }

   @override
   TypeBuilder validateTypeVariableUse(TypeBuilder typeBuilder,
       {required bool allowPotentiallyConstantType}) {
     // ignore: unnecessary_null_comparison
     assert(allowPotentiallyConstantType != null);
     _validateTypeVariableUseInternal(typeBuilder,
         allowPotentiallyConstantType: allowPotentiallyConstantType);
     return typeBuilder;
   }

   void _validateTypeVariableUseInternal(TypeBuilder? builder,
       {required bool allowPotentiallyConstantType}) {
     // ignore: unnecessary_null_comparison
     assert(allowPotentiallyConstantType != null);
     if (builder is NamedTypeBuilder) {
       if (builder.declaration!.isTypeVariable) {
         TypeVariableBuilder typeParameterBuilder =
             builder.declaration as TypeVariableBuilder;
         TypeParameter typeParameter = typeParameterBuilder.parameter;
         if (typeParameter.parent is Class ||
             typeParameter.parent is Extension) {
           switch (builder.instanceTypeVariableAccess) {
             case InstanceTypeVariableAccessState.Allowed:
               if (constantContext != ConstantContext.none &&
                   (!inConstructorInitializer ||
                       !allowPotentiallyConstantType)) {
                 LocatedMessage message =
                     fasta.messageTypeVariableInConstantContext.withLocation(
                         builder.fileUri!,
                         builder.charOffset!,
                         typeParameter.name!.length);
                 builder.bind(new InvalidTypeDeclarationBuilder(
                     typeParameter.name!, message));
                 addProblem(
                     message.messageObject, message.charOffset, message.length);
               }
               break;
             case InstanceTypeVariableAccessState.Disallowed:
               // TODO(johnniwinther): Can we unify this check with the similar
               // check in NamedTypeBuilder.buildTypeInternal. If we skip it
               // here, the error below (type variable in constant context) will
               // be emitted _instead_ of this (type variable in static context),
               // which seems like an odd prioritization.
               // TODO: Handle this case.
               LocatedMessage message = fasta.messageTypeVariableInStaticContext
                   .withLocation(builder.fileUri!, builder.charOffset!,
                       typeParameter.name!.length);
               builder.bind(new InvalidTypeDeclarationBuilder(
                   typeParameter.name!, message));
               addProblem(
                   message.messageObject, message.charOffset, message.length);
               break;
             case InstanceTypeVariableAccessState.Invalid:
               break;
             case InstanceTypeVariableAccessState.Unexpected:
               assert(false,
                   "Unexpected instance type variable $typeParameterBuilder");
               break;
           }
         }
       }
       if (builder.arguments != null) {
         for (TypeBuilder typeBuilder in builder.arguments!) {
           _validateTypeVariableUseInternal(typeBuilder,
               allowPotentiallyConstantType: allowPotentiallyConstantType);
         }
       }
     } else if (builder is FunctionTypeBuilder) {
       _validateTypeVariableUseInternal(builder.returnType,
           allowPotentiallyConstantType: allowPotentiallyConstantType);
       if (builder.formals != null) {
         for (FormalParameterBuilder formalParameterBuilder
             in builder.formals!) {
           _validateTypeVariableUseInternal(formalParameterBuilder.type,
               allowPotentiallyConstantType: allowPotentiallyConstantType);
         }
       }
     }
   }

   @override
   Expression evaluateArgumentsBefore(
       Arguments? arguments, Expression expression) {
     if (arguments == null) return expression;
     List<Expression> expressions =
         new List<Expression>.from(forest.argumentsPositional(arguments));
     for (NamedExpression named in forest.argumentsNamed(arguments)) {
       expressions.add(named.value);
     }
     for (Expression argument in expressions.reversed) {
       expression = new Let(
           new VariableDeclaration.forValue(argument,
               isFinal: true,
               type: coreTypes.objectRawType(libraryBuilder.nullable)),
           expression);
     }
     return expression;
   }

   @override
   bool isIdentical(Member? member) => member == coreTypes.identicalProcedure;

   @override
   Expression buildMethodInvocation(
       Expression receiver, Name name, Arguments arguments, int offset,
       {bool isConstantExpression: false, bool isNullAware: false}) {
     if (constantContext != ConstantContext.none &&
         !isConstantExpression &&
         !enableConstFunctionsInLibrary) {
       return buildProblem(
           fasta.templateNotConstantExpression
               .withArguments('Method invocation'),
           offset,
           name.text.length);
     }
     if (isNullAware) {
       VariableDeclarationImpl variable =
           createVariableDeclarationForValue(receiver);
       return new NullAwareMethodInvocation(
           variable,
           forest.createMethodInvocation(
               offset,
               createVariableGet(variable, receiver.fileOffset),
               name,
               arguments))
         ..fileOffset = receiver.fileOffset;
     } else {
       return forest.createMethodInvocation(offset, receiver, name, arguments);
     }
   }

   @override
   Expression buildSuperInvocation(Name name, Arguments arguments, int offset,
       {bool isConstantExpression: false,
       bool isNullAware: false,
       bool isImplicitCall: false}) {
     if (constantContext != ConstantContext.none &&
         !isConstantExpression &&
         !enableConstFunctionsInLibrary) {
       return buildProblem(
           fasta.templateNotConstantExpression
               .withArguments('Method invocation'),
           offset,
           name.text.length);
     }
     Member? target = lookupInstanceMember(name, isSuper: true);

     if (target == null || (target is Procedure && !target.isAccessor)) {
       if (target == null) {
         warnUnresolvedMethod(name, offset, isSuper: true);
       } else if (!areArgumentsCompatible(target.function!, arguments)) {
         target = null;
         addProblemErrorIfConst(
             fasta.templateSuperclassMethodArgumentMismatch
                 .withArguments(name.text),
             offset,
             name.text.length);
       }
       return new SuperMethodInvocation(name, arguments, target as Procedure?)
         ..fileOffset = offset;
     }
     if (isImplicitCall) {
       return buildProblem(
           fasta.messageImplicitSuperCallOfNonMethod, offset, noLength);
     } else {
       Expression receiver = new SuperPropertyGet(name, target)
         ..fileOffset = offset;
       return forest.createExpressionInvocation(
           arguments.fileOffset, receiver, arguments);
     }
   }

   @override
   void addProblem(Message message, int charOffset, int length,
       {bool wasHandled: false,
       List<LocatedMessage>? context,
       Severity? severity}) {
     libraryBuilder.addProblem(message, charOffset, length, uri,
         wasHandled: wasHandled, context: context, severity: severity);
   }

   @override
   void addProblemErrorIfConst(Message message, int charOffset, int length,
       {bool wasHandled: false, List<LocatedMessage>? context}) {
     // TODO(askesc): Instead of deciding on the severity, this method should
     // take two messages: one to use when a constant expression is
     // required and one to use otherwise.
     Severity severity = message.code.severity;
     if (constantContext != ConstantContext.none) {
       severity = Severity.error;
     }
     addProblem(message, charOffset, length,
         wasHandled: wasHandled, context: context, severity: severity);
   }

   @override
   Expression buildProblemErrorIfConst(
       Message message, int charOffset, int length,
       {bool wasHandled: false, List<LocatedMessage>? context}) {
     addProblemErrorIfConst(message, charOffset, length,
         wasHandled: wasHandled, context: context);
     String text = libraryBuilder.loader.target.context
         .format(message.withLocation(uri, charOffset, length), Severity.error)
         .plain;
     InvalidExpression expression = new InvalidExpression(text)
       ..fileOffset = charOffset;
     return expression;
   }

   @override
   void reportDuplicatedDeclaration(
       Builder existing, String name, int charOffset) {
     List<LocatedMessage>? context = existing.isSynthetic
         ? null
         : <LocatedMessage>[
             fasta.templateDuplicatedDeclarationCause
                 .withArguments(name)
                 .withLocation(
                     existing.fileUri!, existing.charOffset, name.length)
           ];
     addProblem(fasta.templateDuplicatedDeclaration.withArguments(name),
         charOffset, name.length,
         context: context);
   }

   @override
   void debugEvent(String name) {
     // printEvent('BodyBuilder: $name');
   }

   @override
   Expression wrapInDeferredCheck(
       Expression expression, PrefixBuilder prefix, int charOffset) {
     VariableDeclaration check = new VariableDeclaration.forValue(
         forest.checkLibraryIsLoaded(charOffset, prefix.dependency!));
     return new DeferredCheck(check, expression)..fileOffset = charOffset;
   }

   bool isErroneousNode(TreeNode node) {
     return libraryBuilder.loader.handledErrors.isNotEmpty &&
         forest.isErroneousNode(node);
   }

   @override
   DartType buildDartType(TypeBuilder typeBuilder,
       {required bool allowPotentiallyConstantType}) {
     return validateTypeVariableUse(typeBuilder,
             allowPotentiallyConstantType: allowPotentiallyConstantType)
         .build(libraryBuilder);
   }

   @override
   DartType buildTypeLiteralDartType(TypeBuilder typeBuilder,
       {required bool allowPotentiallyConstantType}) {
     return validateTypeVariableUse(typeBuilder,
             allowPotentiallyConstantType: allowPotentiallyConstantType)
         .buildTypeLiteralType(libraryBuilder);
   }

   @override
   List<DartType> buildDartTypeArguments(List<TypeBuilder>? unresolvedTypes,
       {required bool allowPotentiallyConstantType}) {
     if (unresolvedTypes == null) return <DartType>[];
     return new List<DartType>.generate(
         unresolvedTypes.length,
         (int i) => buildDartType(unresolvedTypes[i],
             allowPotentiallyConstantType: allowPotentiallyConstantType),
         growable: true);
   }

   @override
   String constructorNameForDiagnostics(String name,
       {String? className, bool isSuper: false}) {
     if (className == null) {
       Class cls = classBuilder!.cls;
       if (isSuper) {
         cls = cls.superclass!;
         while (cls.isMixinApplication) {
           cls = cls.superclass!;
         }
       }
       className = cls.name;
     }
     return name.isEmpty ? className : "$className.$name";
   }

   @override
   void handleNewAsIdentifier(Token token) {
     if (!libraryBuilder.enableConstructorTearOffsInLibrary) {
       addProblem(
           templateExperimentNotEnabled.withArguments(
               'constructor-tearoffs',
               libraryBuilder.enableConstructorTearOffsVersionInLibrary
                   .toText()),
           token.charOffset,
           token.length);
     }
   }
 }

 abstract class EnsureLoaded {
   void ensureLoaded(Member? member);
   bool isLoaded(Member? member);
 }

 class Operator {
   final Token token;
   String get name => token.stringValue!;

   final int charOffset;

   Operator(this.token, this.charOffset);

   @override
   String toString() => "operator($name)";
 }

 class JumpTarget extends BuilderImpl {
   final List<Statement> users = <Statement>[];

   final JumpTargetKind kind;

   final int functionNestingLevel;

   @override
   final MemberBuilder parent;

   @override
   final int charOffset;

   JumpTarget(
       this.kind, this.functionNestingLevel, this.parent, this.charOffset);

   @override
   Uri get fileUri => parent.fileUri!;

   bool get isBreakTarget => kind == JumpTargetKind.Break;

   bool get isContinueTarget => kind == JumpTargetKind.Continue;

   bool get isGotoTarget => kind == JumpTargetKind.Goto;

   bool get hasUsers => users.isNotEmpty;

   void addBreak(Statement statement) {
     assert(isBreakTarget);
     users.add(statement);
   }

   void addContinue(Statement statement) {
     assert(isContinueTarget);
     users.add(statement);
   }

   void addGoto(Statement statement) {
     assert(isGotoTarget);
     users.add(statement);
   }

   void resolveBreaks(
       Forest forest, LabeledStatement target, Statement targetStatement) {
     assert(isBreakTarget);
     for (Statement user in users) {
       BreakStatementImpl breakStatement = user as BreakStatementImpl;
       breakStatement.target = target;
       breakStatement.targetStatement = targetStatement;
     }
     users.clear();
   }

   List<BreakStatementImpl>? resolveContinues(
       Forest forest, LabeledStatement target) {
     assert(isContinueTarget);
     List<BreakStatementImpl> statements = <BreakStatementImpl>[];
     for (Statement user in users) {
       BreakStatementImpl breakStatement = user as BreakStatementImpl;
       breakStatement.target = target;
       statements.add(breakStatement);
     }
     users.clear();
     return statements;
   }

   void resolveGotos(Forest forest, SwitchCase target) {
     assert(isGotoTarget);
     for (Statement user in users) {
       ContinueSwitchStatement continueSwitchStatement =
           user as ContinueSwitchStatement;
       continueSwitchStatement.target = target;
     }
     users.clear();
   }

   @override
   String get fullNameForErrors => "<jump-target>";
 }

 class LabelTarget extends BuilderImpl implements JumpTarget {
   @override
   final MemberBuilder parent;

   final JumpTarget breakTarget;

   final JumpTarget continueTarget;

   @override
   final int functionNestingLevel;

   @override
   final int charOffset;

   LabelTarget(this.parent, this.functionNestingLevel, this.charOffset)
       : breakTarget = new JumpTarget(
             JumpTargetKind.Break, functionNestingLevel, parent, charOffset),
         continueTarget = new JumpTarget(
             JumpTargetKind.Continue, functionNestingLevel, parent, charOffset);

   @override
   Uri get fileUri => parent.fileUri!;

   @override
   bool get hasUsers => breakTarget.hasUsers || continueTarget.hasUsers;

   @override
   List<Statement> get users => unsupported("users", charOffset, fileUri);

   @override
   JumpTargetKind get kind => unsupported("kind", charOffset, fileUri);

   @override
   bool get isBreakTarget => true;

   @override
   bool get isContinueTarget => true;

   @override
   bool get isGotoTarget => false;

   @override
   void addBreak(Statement statement) {
     breakTarget.addBreak(statement);
   }

   @override
   void addContinue(Statement statement) {
     continueTarget.addContinue(statement);
   }

   @override
   void addGoto(Statement statement) {
     unsupported("addGoto", charOffset, fileUri);
   }

   @override
   void resolveBreaks(
       Forest forest, LabeledStatement target, Statement targetStatement) {
     breakTarget.resolveBreaks(forest, target, targetStatement);
   }

   @override
   List<BreakStatementImpl>? resolveContinues(
       Forest forest, LabeledStatement target) {
     return continueTarget.resolveContinues(forest, target);
   }

   @override
   void resolveGotos(Forest forest, SwitchCase target) {
     unsupported("resolveGotos", charOffset, fileUri);
   }

   @override
   String get fullNameForErrors => "<label-target>";
 }

 class FormalParameters {
   final List<FormalParameterBuilder>? parameters;
   final int charOffset;
   final int length;
   final Uri uri;

   FormalParameters(this.parameters, this.charOffset, this.length, this.uri) {
     if (parameters?.isEmpty ?? false) {
       throw "Empty parameters should be null";
     }
   }

   FunctionNode buildFunctionNode(
       SourceLibraryBuilder library,
       TypeBuilder? returnType,
       List<TypeVariableBuilder>? typeParameters,
       AsyncMarker asyncModifier,
       Statement body,
       int fileEndOffset) {
     FunctionType type = toFunctionType(
             returnType, const NullabilityBuilder.omitted(), typeParameters)
         .build(library) as FunctionType;
     List<VariableDeclaration> positionalParameters = <VariableDeclaration>[];
     List<VariableDeclaration> namedParameters = <VariableDeclaration>[];
     if (parameters != null) {
       for (FormalParameterBuilder parameter in parameters!) {
         if (parameter.isNamed) {
           namedParameters.add(parameter.variable!);
         } else {
           positionalParameters.add(parameter.variable!);
         }
       }
       namedParameters.sort((VariableDeclaration a, VariableDeclaration b) {
         return a.name!.compareTo(b.name!);
       });
     }
     return new FunctionNode(body,
         typeParameters: type.typeParameters,
         positionalParameters: positionalParameters,
         namedParameters: namedParameters,
         requiredParameterCount: type.requiredParameterCount,
         returnType: type.returnType,
         asyncMarker: asyncModifier)
       ..fileOffset = charOffset
       ..fileEndOffset = fileEndOffset;
   }

   TypeBuilder toFunctionType(
       TypeBuilder? returnType, NullabilityBuilder nullabilityBuilder,
       [List<TypeVariableBuilder>? typeParameters]) {
     return new FunctionTypeBuilder(returnType, typeParameters, parameters,
         nullabilityBuilder, uri, charOffset);
   }

   Scope computeFormalParameterScope(
       Scope parent, Builder declaration, ExpressionGeneratorHelper helper) {
     if (parameters == null) return parent;
     assert(parameters!.isNotEmpty);
     Map<String, Builder> local = <String, Builder>{};

     for (FormalParameterBuilder parameter in parameters!) {
       Builder? existing = local[parameter.name];
       if (existing != null) {
         helper.reportDuplicatedDeclaration(
             existing, parameter.name, parameter.charOffset);
       } else {
         local[parameter.name] = parameter;
       }
     }
     return new Scope(
         local: local,
         parent: parent,
         debugName: "formals",
         isModifiable: false);
   }

   @override
   String toString() {
     return "FormalParameters($parameters, $charOffset, $uri)";
   }
 }

 /// Returns a block like this:
 ///
 ///     {
 ///       statement;
 ///       body;
 ///     }
 ///
 /// If [body] is a [Block], it's returned with [statement] prepended to it.
 Block combineStatements(Statement statement, Statement body) {
   if (body is Block) {
     if (statement is Block) {
       body.statements.insertAll(0, statement.statements);
       setParents(statement.statements, body);
     } else {
       body.statements.insert(0, statement);
       statement.parent = body;
     }
     return body;
   } else {
     return new Block(<Statement>[statement, body])
       ..fileOffset = statement.fileOffset;
   }
 }

 /// DartDocTest(
 ///   debugName("myClassName", "myName", "myPrefix"),
 ///   "myPrefix.myClassName.myName"
 /// )
 /// DartDocTest(
 ///   debugName("myClassName", "myName"),
 ///   "myClassName.myName"
 /// )
 /// DartDocTest(
 ///   debugName("myClassName", ""),
 ///   "myClassName"
 /// )
 /// DartDocTest(
 ///   debugName("", ""),
 ///   ""
 /// )
 String debugName(String className, String name, [String? prefix]) {
   String result = name.isEmpty ? className : "$className.$name";
   return prefix == null ? result : "$prefix.$result";
 }

 // TODO(johnniwinther): This is a bit ad hoc. Call sites should know what kind
 // of objects can be anticipated and handle these directly.
 String getNodeName(Object node) {
   if (node is Identifier) {
     return node.name;
   } else if (node is Builder) {
     return node.fullNameForErrors;
   } else if (node is QualifiedName) {
     return flattenName(node, node.charOffset, null);
   } else {
     return unhandled("${node.runtimeType}", "getNodeName", -1, null);
   }
 }

 /// A data holder used to hold the information about a label that is pushed on
 /// the stack.
 class Label {
   String name;
   int charOffset;

   Label(this.name, this.charOffset);

   @override
   String toString() => "label($name)";
 }

 class ForInElements {
   VariableDeclaration? explicitVariableDeclaration;
   VariableDeclaration? syntheticVariableDeclaration;
   Expression? syntheticAssignment;
   Expression? expressionProblem;
   Statement? expressionEffects;

   VariableDeclaration get variable =>
       (explicitVariableDeclaration ?? syntheticVariableDeclaration)!;
 }

 class _BodyBuilderCloner extends CloneVisitorNotMembers {
   final BodyBuilder bodyBuilder;

   _BodyBuilderCloner(this.bodyBuilder);

   @override
   TreeNode visitStaticInvocation(StaticInvocation node) {
     if (node is FactoryConstructorInvocation) {
       FactoryConstructorInvocation result = new FactoryConstructorInvocation(
           node.target, clone(node.arguments),
           isConst: node.isConst)
         ..hasBeenInferred = node.hasBeenInferred;
       bodyBuilder.redirectingFactoryInvocations.add(result);
       return result;
     } else if (node is TypeAliasedFactoryInvocation) {
       TypeAliasedFactoryInvocation result = new TypeAliasedFactoryInvocation(
           node.typeAliasBuilder, node.target, clone(node.arguments),
           isConst: node.isConst)
         ..hasBeenInferred = node.hasBeenInferred;
       bodyBuilder.typeAliasedFactoryInvocations.add(result);
       return result;
     }
     return super.visitStaticInvocation(node);
   }

   @override
   TreeNode visitConstructorInvocation(ConstructorInvocation node) {
     if (node is TypeAliasedConstructorInvocation) {
       TypeAliasedConstructorInvocation result =
           new TypeAliasedConstructorInvocation(
               node.typeAliasBuilder, node.target, clone(node.arguments),
               isConst: node.isConst)
             ..hasBeenInferred = node.hasBeenInferred;
       bodyBuilder.typeAliasedConstructorInvocations.add(result);
       return result;
     }
     return super.visitConstructorInvocation(node);
   }

   @override
   TreeNode visitArguments(Arguments node) {
     if (node is ArgumentsImpl) {
       return ArgumentsImpl.clone(node, node.positional.map(clone).toList(),
           node.named.map(clone).toList(), node.types.map(visitType).toList());
     }
     return super.visitArguments(node);
   }
 }