pkg/kernel/lib/verifier.dart

// 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 kernel.checks;

import 'ast.dart';
import 'target/targets.dart';
import 'type_environment.dart' show StatefulStaticTypeContext, TypeEnvironment;

/// Stages at which verification can occur.
///
/// These can be used to enforce different invariants during different stages
/// of the compilation.
enum VerificationStage {
  /// Verification after the outline compilation.
  outline,

  /// Verification after the body, aka full, compilation, but before pre-
  /// constant evaluation transformations have been performed.
  beforePreConstantEvaluationTransformations,

  /// Verification after pre- constant evaluation transformations have been
  /// performed but before constant evaluation.
  beforeConstantEvaluation,

  /// Verification after constant evaluation but before modular transformations
  /// have been performed.
  afterConstantEvaluation,

  /// Verification after modular transformations have been performed.
  ///
  /// This is final stage of a normal compilation.
  afterModularTransformations,

  /// Verification after global transformations have been performed.
  ///
  /// The global transformation is an additional step performed by some
  /// backends which is not triggered by the front end compilation itself.
  afterGlobalTransformations;

  bool operator <(VerificationStage other) => index < other.index;
  bool operator <=(VerificationStage other) => index <= other.index;
  bool operator >(VerificationStage other) => index > other.index;
  bool operator >=(VerificationStage other) => index >= other.index;
}

/// Interface that defines how the AST is verified.
class Verification {
  const new();

  /// Returns `true` if [node] is allowed to have no file offset.
  bool allowNoFileOffset(VerificationStage stage, TreeNode node) {
    return node is Library;
  }

  /// Returns `true` if [node] is allowed to have location with a file offset
  /// that is not in the range of the enclosing file.
  bool allowInvalidLocation(VerificationStage stage, TreeNode node) {
    return false;
  }
}

void verifyComponent(
  Target target,
  VerificationStage stage,
  Component component, {
  bool skipPlatform = false,
  bool Function(Library library)? librarySkipFilter,
}) {
  VerifyingVisitor.check(
    target,
    stage,
    component,
    skipPlatform: skipPlatform,
    librarySkipFilter: librarySkipFilter,
  );
}

class VerificationErrorListener {
  const new();

  void reportError(
    String details, {
    required TreeNode? node,
    required Uri? problemUri,
    required int? problemOffset,
    required TreeNode? context,
    required TreeNode? origin,
  }) {
    throw new VerificationError(context, node, details);
  }
}

class VerificationError {
  final TreeNode? context;

  final TreeNode? node;

  final String details;

  new(this.context, this.node, this.details);

  @override
  String toString() {
    Location? location;
    try {
      location = node?.location ?? context?.location;
    } catch (_) {
      // TODO(ahe): Fix the compiler instead.
    }
    if (location != null) {
      String file = location.file.toString();
      return "$file:${location.line}:${location.column}: Verification error:"
          " $details";
    } else {
      return "Verification error: $details\n"
          "Context: '$context'.\n"
          "Node: '$node'.";
    }
  }
}

enum TypedefState { Done, BeingChecked }

class VerifyingVisitor {
  static void check(
    Target target,
    VerificationStage stage,
    Component component, {
    required bool skipPlatform,
    bool Function(Library library)? librarySkipFilter,
    VerificationErrorListener listener = const VerificationErrorListener(),
  }) {
    component.accept(
      new _VerifyingVisitor(
        target,
        stage,
        skipPlatform: skipPlatform,
        librarySkipFilter: librarySkipFilter,
        listener: listener,
      ),
    );
  }
}

/// Checks that a kernel component is well-formed.
///
/// This does not include any kind of type checking.
class _VerifyingVisitor extends RecursiveResultVisitor<void> {
  final Target target;

  Uri? fileUri;

  final VerificationErrorListener listener;

  final List<TreeNode> treeNodeStack = <TreeNode>[];
  final bool skipPlatform;
  final bool Function(Library library)? librarySkipFilter;

  final Set<Class> classes = new Set<Class>();
  final Set<Typedef> typedefs = new Set<Typedef>();
  Set<TypeParameter> typeParametersInScope = new Set<TypeParameter>();
  Set<StructuralParameter> structuralParametersInScope =
      new Set<StructuralParameter>();
  Set<Variable> variableDeclarationsInScope = new Set<Variable>();
  final List<Variable> variableStack = <Variable>[];
  final Map<Typedef, TypedefState> typedefState = <Typedef, TypedefState>{};
  final Set<Constant> seenConstants = <Constant>{};
  final Set<Member> _membersSeenByVerifier = new Set.identity();
  final List<Scope> scopeStack = [];

  Map<Reference, ExtensionMemberDescriptor>? _extensionsMembers;
  Map<Reference, ExtensionTypeMemberDescriptor>? _extensionTypeMembers;

  bool classTypeParametersAreInScope = false;

  /// The compilation stage at which this verification is performed.
  final VerificationStage stage;

  AsyncMarker currentAsyncMarker = AsyncMarker.Sync;

  bool inCatchBlock = false;

  bool inUnevaluatedConstant = false;

  bool inConstant = false;

  Library? currentLibrary;

  Member? currentMember;

  Class? currentClass;

  Extension? currentExtension;

  ExtensionTypeDeclaration? currentExtensionTypeDeclaration;

  TreeNode? currentParent;

  TreeNode? get currentClassOrExtensionOrMember =>
      currentMember ??
      currentClass ??
      currentExtension ??
      currentExtensionTypeDeclaration;

  new(
    this.target,
    this.stage, {
    required this.skipPlatform,
    required this.librarySkipFilter,
    required this.listener,
  });

  /// If true, relax certain checks for *outline* mode. For example, don't
  /// attempt to validate constructor initializers.
  bool get isOutline => stage == VerificationStage.outline;

  /// If true, assume that constant evaluation has been performed (with a
  /// target that did not opt out of any of the constant inlining) and report
  /// a verification error for anything that should have been removed by it.
  bool get afterConst => stage >= VerificationStage.afterConstantEvaluation;

  /// If true, constant fields and local variables are expected to be inlined.
  bool get constantsAreAlwaysInlined =>
      target.constantsBackend.alwaysInlineConstants;

  /// If true, constant local variables are expected to have been removed.
  bool get constantLocalsShouldBeRemoved => !target.constantsBackend.keepLocals;

  bool checkVariableInScopeStack(VariableBase node) {
    int occurrenceCount = 0;
    for (Scope scope in scopeStack) {
      for (VariableContext context in scope.contexts) {
        for (VariableBase currentVariable in context.variables) {
          if (identical(currentVariable, node)) {
            occurrenceCount++;
          }
        }
      }
    }

    switch (occurrenceCount) {
      case 1:
        return true;
      case 0:
        if (node is! SyntheticVariable && node.parent is Let) {
          // TODO(johnniwinther,cstefantsova): Let variables are not set up
          // correctly.
          problem(
            node,
            "Variable '${node.cosmeticName}' of the kind "
            "'${node.runtimeType}' wasn't found in the enclosing scopes.",
          );
        }
        return false;
      default:
        problem(
          node,
          "Variable '${node.cosmeticName}' of the kind "
          "'${node.runtimeType}' occurs multiple times "
          "(x${occurrenceCount}) in the enclosing contexts.",
        );
        return false;
    }
  }

  bool checkVariableIsInOwnContext(VariableBase node) {
    VariableContext variableContext;
    try {
      variableContext = node.context;
    } on Error {
      _reportMissingVariableContext(node);
      return false;
    }

    for (VariableBase variable in variableContext.variables) {
      if (identical(node, variable)) {
        return true;
      }
    }
    problem(
      node,
      "Variable '${node.cosmeticName}' of the kind '${node.runtimeType}' "
      "can't be found in its own context.",
    );
    return false;
  }

  void _reportMissingVariableContext(VariableBase node) {
    if (node is! SyntheticVariable && node.parent is Let) {
      // TODO(johnniwinther,cstefantsova): Let variables are not set up
      // correctly.
      problem(
        node,
        "A '${node.runtimeType}' variable with cosmetic name "
        "'${node.cosmeticName}' doesn't have its context set.",
      );
    }
  }

  void enterScopeProvider(ScopeProvider node) {
    if (node.scope case var scope?) {
      scopeStack.add(scope);

      if (target.flags.isClosureContextLoweringEnabled) {
        for (VariableContext context in scope.contexts) {
          for (VariableBase variable in context.variables) {
            VariableContext variableContext;
            try {
              variableContext = variable.context;
            } on Error {
              _reportMissingVariableContext(variable);
              continue;
            }

            if (!identical(context, variableContext)) {
              problem(
                node,
                "Variable '${variable.cosmeticName}' appears in a context "
                "that's not its own.",
              );
            }
          }
        }
      }
    }
  }

  void exitScopeProvider(ScopeProvider node) {
    if (node.scope case var scope?) {
      Scope removedScope = scopeStack.removeLast();
      if (!identical(removedScope, scope)) {
        // TODO(cstefantsova): This looks like an internal error. Should we
        // report it differently?
        problem(
          node,
          "Top scope on the stack doesn't match the scope of the exited "
          "ScopeProvider object ('${node.runtimeType}').",
        );
      }
    }
  }

  @override
  void defaultTreeNode(TreeNode node) {
    enterTreeNode(node);
    visitChildren(node);
    exitTreeNode(node);
  }

  @override
  void defaultConstantReference(Constant constant) {
    if (seenConstants.add(constant)) {
      constant.accept(this);
    }
  }

  @override
  void defaultConstant(Constant constant) {
    constant.visitChildren(this);
  }

  void problem(
    TreeNode? node,
    String details, {
    TreeNode? context,
    TreeNode? origin,
  }) {
    TreeNode? problemNode = node ?? context ?? currentClassOrExtensionOrMember;
    int offset = problemNode?.fileOffset ?? -1;
    Location? location = problemNode != null
        ? _getLocation(problemNode, allowInvalidLocation: true)
        : null;
    Uri? file = location?.file ?? fileUri;
    Uri? uri = file == null ? null : file;
    String verifierState = 'Target=${target.name}, $stage: ';
    listener.reportError(
      '$verifierState$details',
      problemUri: uri,
      problemOffset: offset,
      node: node,
      context: context ?? currentClassOrExtensionOrMember,
      origin: origin,
    );
  }

  TreeNode? enterParent(TreeNode node) {
    if (!identical(node.parent, currentParent)) {
      problem(
        node,
        "Incorrect parent pointer on ${node}:"
        " expected ${currentParent},"
        " but found: ${node.parent}.",
        context: currentParent,
      );
    }
    TreeNode? oldParent = currentParent;
    currentParent = node;
    return oldParent;
  }

  void exitParent(TreeNode? oldParent) {
    currentParent = oldParent;
  }

  int enterLocalScope() => variableStack.length;

  void exitLocalScope(int stackHeight) {
    for (int i = stackHeight; i < variableStack.length; ++i) {
      undeclareVariable(variableStack[i]);
    }
    variableStack.length = stackHeight;
  }

  /// Calls [f] with [node] set up as the parent node.
  void inTreeNode(TreeNode node, void Function() f) {
    TreeNode? oldParent = enterParent(node);
    f();
    exitParent(oldParent);
  }

  void visitChildren(TreeNode node) {
    inTreeNode(node, () => node.visitChildren(this));
  }

  void visitWithLocalScope(TreeNode node) {
    enterTreeNode(node);
    int stackHeight = enterLocalScope();
    visitChildren(node);
    exitLocalScope(stackHeight);
    exitTreeNode(node);
  }

  void declareVariable(Variable variable) {
    if (variableDeclarationsInScope.contains(variable)) {
      problem(variable, "Variable '$variable' declared more than once.");
    }
    variableDeclarationsInScope.add(variable);
    variableStack.add(variable);
  }

  void undeclareVariable(Variable variable) {
    variableDeclarationsInScope.remove(variable);
  }

  void declareTypeParameters(List<TypeParameter> parameters) {
    for (int i = 0; i < parameters.length; ++i) {
      TypeParameter parameter = parameters[i];
      if (identical(parameter.bound, TypeParameter.unsetBoundSentinel)) {
        problem(
          currentParent,
          "Missing bound for type parameter '$parameter'.",
        );
      }
      if (identical(
        parameter.defaultType,
        TypeParameter.unsetDefaultTypeSentinel,
      )) {
        problem(
          currentParent,
          "Missing default type for type parameter '$parameter'.",
        );
      }
      if (!typeParametersInScope.add(parameter)) {
        problem(parameter, "Type parameter '$parameter' redeclared.");
      }
    }
  }

  void declareStructuralParameters(List<StructuralParameter> parameters) {
    for (int i = 0; i < parameters.length; ++i) {
      StructuralParameter parameter = parameters[i];
      if (identical(parameter.bound, StructuralParameter.unsetBoundSentinel)) {
        problem(
          currentParent,
          "Missing bound for type parameter '$parameter'.",
        );
      }
      if (identical(
        parameter.defaultType,
        StructuralParameter.unsetDefaultTypeSentinel,
      )) {
        problem(
          currentParent,
          "Missing default type for type parameter '$parameter'.",
        );
      }
      if (!structuralParametersInScope.add(parameter)) {
        problem(currentParent, "Type parameter '$parameter' redeclared.");
      }
    }
  }

  void undeclareTypeParameters(List<TypeParameter> parameters) {
    typeParametersInScope.removeAll(parameters);
  }

  void undeclareStructuralParameters(List<StructuralParameter> parameters) {
    structuralParametersInScope.removeAll(parameters);
  }

  void checkVariableInScope(Variable variable, TreeNode where) {
    // TODO(cstefantsova): Support new variable model.
    if (!target.flags.isClosureContextLoweringEnabled &&
        !variableDeclarationsInScope.contains(variable)) {
      problem(where, "Variable '$variable' used out of scope.");
    }
  }

  void _declareMember(Member member) {
    if (!_membersSeenByVerifier.add(member)) {
      problem(
        member.function,
        "Member '$member' has been declared more than once.",
      );
    }
  }

  @override
  void visitComponent(Component component) {
    for (Library library in component.libraries) {
      for (Class class_ in library.classes) {
        if (!classes.add(class_)) {
          problem(class_, "Class '$class_' declared more than once.");
        }
      }
      for (Typedef typedef_ in library.typedefs) {
        if (!typedefs.add(typedef_)) {
          problem(typedef_, "Typedef '$typedef_' declared more than once.");
        }
      }

      library.forEachMember(_declareMember);
      for (Class class_ in library.classes) {
        class_.forEachMember(_declareMember);
      }
      for (ExtensionTypeDeclaration extensionTypeDeclaration
          in library.extensionTypeDeclarations) {
        extensionTypeDeclaration.procedures.forEach(_declareMember);
      }
    }
    visitChildren(component);
  }

  @override
  void visitLibrary(Library node) {
    if (skipPlatform &&
        node.importUri.isScheme('dart') &&
        // 'dart:test' is used in the unit tests and isn't an actual part of the
        // platform so we don't skip its verification.
        node.importUri.path != 'test') {
      return;
    }
    if (librarySkipFilter != null && librarySkipFilter!(node)) {
      return;
    }

    enterTreeNode(node);
    fileUri = checkLocation(node, node.name, node.fileUri);
    currentLibrary = node;
    TreeNode? oldParent = enterParent(node);
    _visitAnnotations(node.annotations);
    visitList(node.dependencies, this);
    visitList(node.parts, this);
    visitList(node.typedefs, this);
    visitList(node.classes, this);
    visitList(node.extensions, this);
    visitList(node.extensionTypeDeclarations, this);
    visitList(node.procedures, this);
    visitList(node.fields, this);
    exitParent(oldParent);
    currentLibrary = null;
    exitTreeNode(node);
    _extensionsMembers = null;
    _extensionTypeMembers = null;
  }

  Map<Reference, ExtensionMemberDescriptor> _computeExtensionMembers(
    Library library,
  ) {
    if (_extensionsMembers == null) {
      Map<Reference, ExtensionMemberDescriptor> map = _extensionsMembers = {};
      for (Extension extension in library.extensions) {
        for (ExtensionMemberDescriptor descriptor
            in extension.memberDescriptors) {
          Reference? memberReference = descriptor.memberReference;
          if (memberReference != null) {
            map[memberReference] = descriptor;
            Member member = memberReference.asMember;
            if (!member.isExtensionMember) {
              problem(
                member,
                "Member $member (${descriptor}) from $extension is not "
                " marked as an extension member.",
              );
            }
          }
          Reference? tearOffReference = descriptor.tearOffReference;
          if (tearOffReference != null) {
            map[tearOffReference] = descriptor;
            Member tearOff = tearOffReference.asMember;
            if (!tearOff.isExtensionMember) {
              problem(
                tearOff,
                "Tear-off $tearOff (${descriptor}) from $extension is not "
                "marked as an extension member.",
              );
            }
          }
          if (memberReference == null && tearOffReference == null) {
            problem(
              extension,
              "Both member and tear-off references are null in "
              "the descriptor $descriptor from $extension.",
            );
          }
        }
      }
    }
    return _extensionsMembers!;
  }

  @override
  void visitLibraryPart(LibraryPart node) {
    enterTreeNode(node);
    TreeNode? oldParent = enterParent(node);
    _visitAnnotations(node.annotations);
    exitParent(oldParent);
    exitTreeNode(node);
  }

  @override
  void visitLibraryDependency(LibraryDependency node) {
    enterTreeNode(node);
    TreeNode? oldParent = enterParent(node);
    _visitAnnotations(node.annotations);
    visitList(node.combinators, this);
    exitParent(oldParent);
    exitTreeNode(node);
  }

  Map<Reference, ExtensionTypeMemberDescriptor> _computeExtensionTypeMembers(
    Library library,
  ) {
    if (_extensionTypeMembers == null) {
      Map<Reference, ExtensionTypeMemberDescriptor> map =
          _extensionTypeMembers = {};
      for (ExtensionTypeDeclaration extensionTypeDeclaration
          in library.extensionTypeDeclarations) {
        for (ExtensionTypeMemberDescriptor descriptor
            in extensionTypeDeclaration.memberDescriptors) {
          Reference? memberReference = descriptor.memberReference;
          if (memberReference != null) {
            map[memberReference] = descriptor;
            Member member = memberReference.asMember;
            if (!member.isExtensionTypeMember) {
              problem(
                member,
                "Member $member (${descriptor}) from "
                "$extensionTypeDeclaration is not marked as an extension "
                "type member.",
              );
            }
          }
          Reference? tearOffReference = descriptor.tearOffReference;
          if (tearOffReference != null) {
            map[tearOffReference] = descriptor;
            Member tearOff = tearOffReference.asMember;
            if (!tearOff.isExtensionTypeMember) {
              problem(
                tearOff,
                "Tear-off $tearOff (${descriptor}) from "
                "$extensionTypeDeclaration is not marked as an extension "
                "type member.",
              );
            }
          }
          if (memberReference == null && tearOffReference == null) {
            problem(
              extensionTypeDeclaration,
              "Both member and tear-off references are null in "
              "the descriptor $descriptor from $extensionTypeDeclaration.",
            );
          }
        }
      }
    }
    return _extensionTypeMembers!;
  }

  @override
  void visitExtension(Extension node) {
    enterTreeNode(node);
    fileUri = checkLocation(node, node.name, node.fileUri);
    currentExtension = node;
    _computeExtensionMembers(node.enclosingLibrary);
    declareTypeParameters(node.typeParameters);
    final TreeNode? oldParent = enterParent(node);
    _visitAnnotations(node.annotations);
    visitList(node.typeParameters, this);
    node.onType.accept(this);
    exitParent(oldParent);
    undeclareTypeParameters(node.typeParameters);
    currentExtension = null;
    exitTreeNode(node);
  }

  @override
  void visitExtensionTypeDeclaration(ExtensionTypeDeclaration node) {
    enterTreeNode(node);
    fileUri = checkLocation(node, node.name, node.fileUri);
    currentExtensionTypeDeclaration = node;
    _computeExtensionTypeMembers(node.enclosingLibrary);
    declareTypeParameters(node.typeParameters);
    final TreeNode? oldParent = enterParent(node);
    for (DartType type in node.implements) {
      if (!(type is ExtensionType || type is InterfaceType)) {
        problem(
          node,
          "Extension type can only implement extension types and interface "
          "types. Found $type.",
        );
      } else if (type is ExtensionType &&
              type.nullability == Nullability.nullable ||
          type is! ExtensionType && type.isPotentiallyNullable) {
        problem(
          node,
          "Extension type can only implement non-nullable types. "
          "Found $type.",
        );
      }
    }
    _visitAnnotations(node.annotations);
    visitList(node.typeParameters, this);
    node.declaredRepresentationType.accept(this);
    visitList(node.procedures, this);
    exitParent(oldParent);
    undeclareTypeParameters(node.typeParameters);
    currentExtensionTypeDeclaration = null;
    exitTreeNode(node);
  }

  void checkTypedef(Typedef node) {
    TypedefState? state = typedefState[node];
    if (state == TypedefState.Done) return;
    if (state == TypedefState.BeingChecked) {
      problem(node, "The typedef '$node' refers to itself", context: node);
    }
    assert(state == null);
    enterTreeNode(node);
    typedefState[node] = TypedefState.BeingChecked;
    Set<TypeParameter> savedTypeParameters = typeParametersInScope;
    typeParametersInScope = node.typeParameters.toSet();
    TreeNode? savedParent = currentParent;
    currentParent = node;
    // Visit children without checking the parent pointer on the typedef itself
    // since this can be called from a context other than its true parent.
    _visitAnnotations(node.annotations);
    visitList(node.typeParameters, this);
    node.type?.accept(this);
    currentParent = savedParent;
    typeParametersInScope = savedTypeParameters;
    typedefState[node] = TypedefState.Done;
    exitTreeNode(node);
  }

  @override
  void visitTypedef(Typedef node) {
    enterTreeNode(node);
    fileUri = checkLocation(node, node.name, node.fileUri);
    checkTypedef(node);
    // Enter and exit the node to check the parent pointer on the typedef node.
    exitParent(enterParent(node));
    exitTreeNode(node);
  }

  void _findExtensionMember(Member node) {
    assert(node.isExtensionMember);
    Map<Reference, ExtensionMemberDescriptor> extensionMembers =
        _computeExtensionMembers(node.enclosingLibrary);
    if (!extensionMembers.containsKey(node.reference)) {
      problem(
        node,
        "Extension member $node is not found in any extension of the "
        "enclosing library.",
      );
    }
  }

  void _findExtensionTypeMember(Member node) {
    assert(node.isExtensionTypeMember);
    Map<Reference, ExtensionTypeMemberDescriptor> extensionTypeMembers =
        _computeExtensionTypeMembers(node.enclosingLibrary);
    if (node is Procedure &&
        node.stubKind == ProcedureStubKind.RepresentationField) {
      if (extensionTypeMembers.containsKey(node.reference)) {
        problem(
          node,
          "Extension type representation field $node is found amongst the "
          "lowered extension type members of the enclosing library.",
        );
      }
    } else {
      if (!extensionTypeMembers.containsKey(node.reference)) {
        problem(
          node,
          "Extension type member $node is not found in any extension type "
          "declaration of the enclosing library.",
        );
      }
    }
  }

  @override
  void visitField(Field node) {
    enterTreeNode(node);
    enterScopeProvider(node);
    fileUri = checkLocation(node, node.name.text, node.fileUri);
    currentMember = node;
    TreeNode? oldParent = enterParent(node);
    bool isTopLevel = node.parent == currentLibrary;
    if (isTopLevel && !node.isStatic) {
      problem(
        node,
        "The top-level field '${node.name.text}' should be static",
        context: node,
      );
    }
    if (node.isConst && !node.isStatic) {
      problem(
        node,
        "The const field '${node.name.text}' should be static",
        context: node,
      );
    }
    bool isImmutable = node.isLate
        ? (node.isFinal && node.initializer != null)
        : (node.isFinal || node.isConst);
    if (isImmutable == node.hasSetter) {
      if (node.hasSetter) {
        problem(
          node,
          "The immutable field '${node.name.text}' has a setter reference",
          context: node,
        );
      } else {
        if (isOutline && node.isLate) {
          // TODO(johnniwinther): Should we add a flag on Field for having
          // a declared initializer?
          // The initializer is not included in the outline so we can't tell
          // whether it has an initializer or not.
        } else {
          problem(
            node,
            "The mutable field '${node.name.text}' has no setter reference",
            context: node,
          );
        }
      }
    }
    if (node.isExtensionMember) {
      _findExtensionMember(node);
    }
    if (node.isExtensionTypeMember) {
      _findExtensionTypeMember(node);
    }
    classTypeParametersAreInScope = !node.isStatic;
    node.thisVariable?.accept(this);
    node.initializer?.accept(this);
    node.type.accept(this);
    classTypeParametersAreInScope = false;
    _visitAnnotations(node.annotations);
    exitParent(oldParent);
    currentMember = null;
    exitScopeProvider(node);
    exitTreeNode(node);
  }

  void _visitAnnotations(List<Expression> annotations) {
    for (Expression annotation in annotations) {
      if (stage >= VerificationStage.afterConstantEvaluation) {
        if (!(annotation is ConstantExpression ||
            annotation is InvalidExpression)) {
          problem(
            annotation,
            "Unexpected annotation $annotation (${annotation.runtimeType}). "
            "Expected a ConstantExpression or InvalidExpression.",
          );
        }
      }
      annotation.accept(this);
    }
  }

  @override
  void visitProcedure(Procedure node) {
    enterTreeNode(node);
    fileUri = checkLocation(node, node.name.text, node.fileUri);
    if (node.isExtensionMember) {
      _findExtensionMember(node);
    }
    if (node.isExtensionTypeMember) {
      _findExtensionTypeMember(node);
    }

    if (node.isRedirectingFactory &&
        node.function.redirectingFactoryTarget == null) {
      problem(
        node,
        "Procedure '${node.name}' doesn't have a redirecting "
        "factory target, but has the 'isRedirectingFactory' bit set.",
      );
    } else if (!node.isRedirectingFactory &&
        node.function.redirectingFactoryTarget != null) {
      problem(
        node,
        "Procedure '${node.name}' has redirecting factory target, but "
        "doesn't have the 'isRedirectingFactory' bit set.",
      );
    }

    currentMember = node;
    TreeNode? oldParent = enterParent(node);
    classTypeParametersAreInScope = !node.isStatic;
    if (node.isAbstract && node.isExternal) {
      problem(node, "Procedure cannot be both abstract and external.");
    }
    if (node.isMemberSignature && node.isForwardingStub) {
      problem(
        node,
        "Procedure cannot be both a member signature and a forwarding stub: "
        "$node.",
      );
    }
    if (node.isMemberSignature && node.isForwardingSemiStub) {
      problem(
        node,
        "Procedure cannot be both a member signature and a forwarding semi "
        "stub $node.",
      );
    }
    if (node.isMemberSignature && node.isNoSuchMethodForwarder) {
      problem(
        node,
        "Procedure cannot be both a member signature and a noSuchMethod "
        "forwarder $node.",
      );
    }
    if (node.isMemberSignature && node.memberSignatureOrigin == null) {
      problem(
        node,
        "Member signature must have a member signature origin $node.",
      );
    }
    if (node.abstractForwardingStubTarget != null &&
        !(node.isForwardingStub || node.isForwardingSemiStub)) {
      problem(
        node,
        "Only forwarding stubs can have a forwarding stub interface target "
        "$node.",
      );
    }
    if (node.concreteForwardingStubTarget != null &&
        !(node.isForwardingStub || node.isForwardingSemiStub)) {
      problem(
        node,
        "Only forwarding stubs can have a forwarding stub super target "
        "$node.",
      );
    }
    node.function.accept(this);
    classTypeParametersAreInScope = false;
    _visitAnnotations(node.annotations);
    exitParent(oldParent);
    // TODO(johnniwinther): Enable this invariant. Possibly by removing bodies
    // from external procedures declared with a body or by removing the external
    // flag from such procedures.
    /*if (node.isExternal) {
      if (node.function.body != null) {
        problem(node, "External procedure has non-null body.");
      }
    } else if (node.isAbstract) {
      if (node.function.body != null) {
        problem(node, "Abstract procedure has non-null body.");
      }
    } else {
      if (node.function.body == null) {
        problem(node, "Non-external/abstract procedure has no body.");
      }
    }*/
    currentMember = null;
    exitTreeNode(node);
  }

  @override
  void visitConstructor(Constructor node) {
    enterTreeNode(node);
    enterScopeProvider(node.function);
    fileUri = checkLocation(node, node.name.text, node.fileUri);
    currentMember = node;
    classTypeParametersAreInScope = true;
    if (node.isExtensionMember) {
      _findExtensionMember(node);
    }
    if (node.isExtensionTypeMember) {
      _findExtensionTypeMember(node);
    }

    // The constructor member needs special treatment due to parameters being
    // in scope in the initializer list.
    TreeNode? oldParent = enterParent(node);
    int stackHeight = enterLocalScope();
    visitChildren(node.function);
    visitList(node.initializers, this);
    if (!isOutline) {
      checkInitializers(node);
    }
    exitLocalScope(stackHeight);
    classTypeParametersAreInScope = false;
    _visitAnnotations(node.annotations);
    exitParent(oldParent);
    // TODO(johnniwinther): Enable this invariant. Possibly by removing bodies
    // from external constructors declared with a body or by removing the
    // external flag from such constructors.
    /*if (node.isExternal) {
      if (node.function.body != null) {
        problem(node, "External constructor has non-null body.");
      }
    } else {
      if (node.function.body == null) {
        problem(node, "Non-external constructor has no body.");
      }
    }*/
    classTypeParametersAreInScope = false;
    currentMember = null;
    exitScopeProvider(node.function);
    exitTreeNode(node);
  }

  @override
  void visitClass(Class node) {
    enterTreeNode(node);
    fileUri = checkLocation(node, node.name, node.fileUri);
    currentClass = node;
    declareTypeParameters(node.typeParameters);
    TreeNode? oldParent = enterParent(node);
    classTypeParametersAreInScope = false;
    _visitAnnotations(node.annotations);
    classTypeParametersAreInScope = true;
    visitList(node.typeParameters, this);
    visitList(node.fields, this);
    visitList(node.constructors, this);
    visitList(node.procedures, this);
    exitParent(oldParent);
    undeclareTypeParameters(node.typeParameters);
    currentClass = null;
    exitTreeNode(node);
  }

  @override
  void visitFunctionNode(FunctionNode node) {
    enterTreeNode(node);
    enterScopeProvider(node);
    declareTypeParameters(node.typeParameters);
    bool savedInCatchBlock = inCatchBlock;
    AsyncMarker savedAsyncMarker = currentAsyncMarker;
    currentAsyncMarker = node.asyncMarker;
    if (!isOutline) {
      if (node.asyncMarker == AsyncMarker.Async &&
          node.emittedValueType == null) {
        problem(
          node,
          "No future value type set for async function in opt-in library.",
        );
      }

      TreeNode? parent = node.parent;
      if (parent is! Procedure ||
          !parent.isAbstract &&
              !parent.isSynthetic &&
              !parent.isSyntheticForwarder) {
        for (
          int positionalIndex = 0;
          positionalIndex < node.positionalParameters.length;
          positionalIndex++
        ) {
          if (positionalIndex >= node.requiredParameterCount) {
            PositionalParameter positionalParameter =
                node.positionalParameters[positionalIndex];
            if (positionalParameter.defaultValue == null &&
                // Global transformations like TFA may not maintain this
                // invariant.
                stage != VerificationStage.afterGlobalTransformations) {
              problem(
                positionalParameter,
                "An optional positional parameter is expected to have a "
                "default value initializer, defined or synthesized.",
              );
            }
          }
        }
        for (NamedParameter namedParameter in node.namedParameters) {
          if (!namedParameter.isRequired &&
              namedParameter.defaultValue == null &&
              // Global transformations like TFA may not maintain this
              // invariant.
              stage != VerificationStage.afterGlobalTransformations) {
            problem(
              namedParameter,
              "An optional named parameter is expected to have a default "
              "value initializer, defined or synthesized.",
            );
          }
        }
      }
    }
    inCatchBlock = false;
    visitWithLocalScope(node);
    inCatchBlock = savedInCatchBlock;
    currentAsyncMarker = savedAsyncMarker;
    undeclareTypeParameters(node.typeParameters);
    exitScopeProvider(node);
    exitTreeNode(node);
  }

  @override
  void visitFunctionType(FunctionType node) {
    for (int i = 1; i < node.namedParameters.length; ++i) {
      if (node.namedParameters[i - 1].compareTo(node.namedParameters[i]) >= 0) {
        problem(
          currentParent,
          "Named parameters are not sorted on function type ($node).",
        );
      }
    }
    declareStructuralParameters(node.typeParameters);
    visitList(node.positionalParameters, this);
    visitList(node.namedParameters, this);
    node.returnType.accept(this);
    undeclareStructuralParameters(node.typeParameters);
  }

  @override
  void visitBlock(Block node) {
    enterScopeProvider(node);
    visitWithLocalScope(node);
    exitScopeProvider(node);
  }

  @override
  void visitForStatement(ForStatement node) {
    enterScopeProvider(node);
    visitWithLocalScope(node);
    exitScopeProvider(node);
  }

  @override
  void visitForInStatement(ForInStatement node) {
    enterScopeProvider(node);
    visitWithLocalScope(node);
    exitScopeProvider(node);
  }

  @override
  void visitWhileStatement(WhileStatement node) {
    enterScopeProvider(node);
    visitWithLocalScope(node);
    exitScopeProvider(node);
  }

  @override
  void visitLet(Let node) {
    if (_isCompileTimeErrorEncoding(node)) return;
    visitWithLocalScope(node);
  }

  @override
  void visitInvalidExpression(InvalidExpression node) {
    return;
  }

  @override
  void visitBlockExpression(BlockExpression node) {
    enterTreeNode(node);
    enterScopeProvider(node);
    int stackHeight = enterLocalScope();
    // Do not visit the block directly because the value expression needs to
    // be in its scope.
    TreeNode? oldParent = enterParent(node);
    enterParent(node.body);
    for (int i = 0; i < node.body.statements.length; ++i) {
      node.body.statements[i].accept(this);
    }
    exitParent(node);
    node.value.accept(this);
    exitParent(oldParent);
    exitLocalScope(stackHeight);
    exitScopeProvider(node);
    exitTreeNode(node);
  }

  @override
  void visitCatch(Catch node) {
    enterScopeProvider(node);
    bool savedInCatchBlock = inCatchBlock;
    inCatchBlock = true;
    visitWithLocalScope(node);
    inCatchBlock = savedInCatchBlock;
    exitScopeProvider(node);
  }

  @override
  void visitReturnStatement(ReturnStatement node) {
    switch (currentAsyncMarker) {
      case AsyncMarker.Sync:
      case AsyncMarker.Async:
        // ok
        break;
      case AsyncMarker.SyncStar:
      case AsyncMarker.AsyncStar:
        if (node.expression != null) {
          problem(
            node,
            "Return statement in function with async marker: "
            "$currentAsyncMarker",
          );
        }
        break;
    }
    super.visitReturnStatement(node);
  }

  @override
  void visitYieldStatement(YieldStatement node) {
    switch (currentAsyncMarker) {
      case AsyncMarker.Sync:
      case AsyncMarker.Async:
        problem(
          node,
          "Yield statement in function with async marker: "
          "$currentAsyncMarker",
        );
        break;
      case AsyncMarker.SyncStar:
      case AsyncMarker.AsyncStar:
        // ok
        break;
    }
    super.visitYieldStatement(node);
  }

  @override
  void visitRethrow(Rethrow node) {
    if (!inCatchBlock) {
      problem(node, "Rethrow must be inside a Catch block.");
    }
  }

  @override
  void defaultVariable(Variable node) {
    return _verifyVariableDeclaration(node);
  }

  void _verifyVariableDeclaration(Variable node) {
    enterTreeNode(node);
    visitChildren(node);
    declareVariable(node);
    if (afterConst && node.isConst && constantLocalsShouldBeRemoved) {
      Expression? initializer = node.initializer;
      if (!(initializer is InvalidExpression ||
          initializer is ConstantExpression &&
              initializer.constant is UnevaluatedConstant)) {
        problem(node, "Constant VariableDeclaration");
      }
    }
    exitTreeNode(node);
  }

  @override
  void visitCatchVariable(CatchVariable node) {
    _verifyVariable(node);
  }

  @override
  void visitLocalVariable(LocalVariable node) {
    _verifyVariable(node);
  }

  @override
  void visitLocalFunctionVariable(LocalFunctionVariable node) {
    _verifyVariable(node);
  }

  @override
  void visitLateVariable(LateVariable node) {
    _verifyVariable(node);
  }

  @override
  void visitConstVariable(ConstVariable node) {
    _verifyVariable(node);
  }

  @override
  void visitPositionalParameter(PositionalParameter node) {
    // TODO(johnniwinther): Verify that only optional parameters have default
    //  values.
    _verifyVariable(node);
  }

  @override
  void visitNamedParameter(NamedParameter node) {
    // TODO(johnniwinther): Verify that only optional parameters have default
    //  values.
    _verifyVariable(node);
  }

  @override
  void visitSyntheticVariable(SyntheticVariable node) {
    _verifyVariable(node);
  }

  @override
  void visitThisVariable(ThisVariable node) {
    _verifyVariable(node);
  }

  void _verifyVariable(Variable node) {
    enterTreeNode(node);
    TreeNode? oldParent = enterParent(node);
    _visitAnnotations(node.annotations);
    exitParent(oldParent);
    declareVariable(node);
    exitTreeNode(node);

    if (target.flags.isClosureContextLoweringEnabled && !isOutline) {
      checkVariableInScopeStack(node);
      checkVariableIsInOwnContext(node);
    }
  }

  @override
  void visitVariableGet(VariableGet node) {
    enterTreeNode(node);
    checkVariableInScope(node.variable, node);
    visitChildren(node);
    if (constantsAreAlwaysInlined &&
        afterConst &&
        node.variable.isConst &&
        !inUnevaluatedConstant) {
      problem(node, "VariableGet of const variable '${node.variable}'.");
    }
    exitTreeNode(node);
  }

  @override
  void visitVariableSet(VariableSet node) {
    enterTreeNode(node);
    checkVariableInScope(node.variable, node);
    visitChildren(node);
    exitTreeNode(node);
  }

  @override
  void visitStaticGet(StaticGet node) {
    enterTreeNode(node);
    visitChildren(node);
    // TODO(johnniwinther): Can this be deleted now?
    // Currently Constructor.hasGetter returns `false` even though the CFE uses
    // it as a getter for internal purposes:
    //
    // CFE is letting all call site of a redirecting constructor be resolved
    // to the real target.  In order to resolve it, it seems to add a body into
    // the redirecting-factory constructor which caches the target constructor.
    // That cache is via a `StaticGet(real-constructor)` node, which we make
    // here pass the verifier.
    if (!node.target.hasGetter && node.target is! Constructor) {
      problem(node, "StaticGet of '${node.target}' without getter.");
    }
    if (node.target.isInstanceMember) {
      problem(node, "StaticGet of '${node.target}' that's an instance member.");
    }
    if (constantsAreAlwaysInlined &&
        afterConst &&
        node.target is Field &&
        node.target.isConst) {
      problem(node, "StaticGet of const field '${node.target}'.");
    }
    exitTreeNode(node);
  }

  @override
  void visitStaticSet(StaticSet node) {
    enterTreeNode(node);
    visitChildren(node);
    if (!node.target.hasSetter) {
      problem(node, "StaticSet to '${node.target}' without setter.");
    }
    if (node.target.isInstanceMember) {
      problem(node, "StaticSet to '${node.target}' that's an instance member.");
    }
    exitTreeNode(node);
  }

  @override
  void visitStaticInvocation(StaticInvocation node) {
    enterTreeNode(node);
    checkTargetedInvocation(node.target, node);
    if (node.target.isInstanceMember) {
      problem(
        node,
        "StaticInvocation of '${node.target}' that's an instance member.",
      );
    }
    if (node.isConst &&
        !(node.target.isConst &&
            node.target.isExternal &&
            node.target.kind == ProcedureKind.Factory) &&
        !(node.target.isConst && node.target.isExtensionTypeMember)) {
      problem(
        node,
        "Constant StaticInvocation of '${node.target}' that isn't"
        " a const external factory or a const extension type constructor.",
      );
    }
    if (afterConst && node.isConst && !inUnevaluatedConstant) {
      problem(node, "Constant StaticInvocation.");
    }
    exitTreeNode(node);
  }

  @override
  void visitTypedefTearOff(TypedefTearOff node) {
    _checkTypedefTearOff(node);
    declareStructuralParameters(node.structuralParameters);
    super.visitTypedefTearOff(node);
    undeclareStructuralParameters(node.structuralParameters);
  }

  void checkTargetedInvocation(Member target, InvocationExpression node) {
    visitChildren(node);
    if (target.function == null) {
      problem(node, "${node.runtimeType} without function.");
    }
    if (!areArgumentsCompatible(node.arguments, target.function!)) {
      problem(
        node,
        "${node.runtimeType} with incompatible arguments for '${target}'.",
      );
    }
    int expectedTypeParameters = target is Constructor
        ? target.enclosingClass.typeParameters.length
        : target.function!.typeParameters.length;
    if (node.arguments.types.length != expectedTypeParameters) {
      problem(
        node,
        "${node.runtimeType} with wrong number of type arguments"
        " for '${target}'.",
      );
    }
  }

  @override
  void visitConstructorInvocation(ConstructorInvocation node) {
    enterTreeNode(node);
    checkTargetedInvocation(node.target, node);
    if (node.target.enclosingClass.isAbstract) {
      problem(node, "$node of abstract class ${node.target.enclosingClass}.");
    }
    if (node.isConst && !node.target.isConst) {
      problem(
        node,
        "Constant ConstructorInvocation fo '${node.target}' that"
        " isn't const.",
      );
    }
    if (afterConst && node.isConst && !inUnevaluatedConstant) {
      problem(node, "Invocation of const constructor '${node.target}'.");
    }
    exitTreeNode(node);
  }

  bool areArgumentsCompatible(Arguments arguments, FunctionNode function) {
    if (arguments.positional.length < function.requiredParameterCount) {
      return false;
    }
    if (arguments.positional.length > function.positionalParameters.length) {
      return false;
    }
    namedLoop:
    for (int i = 0; i < arguments.named.length; ++i) {
      NamedExpression argument = arguments.named[i];
      String name = argument.name;
      for (int j = 0; j < function.namedParameters.length; ++j) {
        if (function.namedParameters[j].parameterName == name) {
          continue namedLoop;
        }
      }
      return false;
    }
    return true;
  }

  @override
  void visitListLiteral(ListLiteral node) {
    enterTreeNode(node);
    visitChildren(node);
    if (afterConst && node.isConst && !inUnevaluatedConstant) {
      problem(node, "Constant list literal.");
    }
    exitTreeNode(node);
  }

  @override
  void visitSetLiteral(SetLiteral node) {
    enterTreeNode(node);
    visitChildren(node);
    if (afterConst && node.isConst && !inUnevaluatedConstant) {
      problem(node, "Constant set literal.");
    }
    exitTreeNode(node);
  }

  @override
  void visitMapLiteral(MapLiteral node) {
    enterTreeNode(node);
    visitChildren(node);
    if (afterConst && node.isConst && !inUnevaluatedConstant) {
      problem(node, "Constant map literal.");
    }
    exitTreeNode(node);
  }

  @override
  void visitSymbolLiteral(SymbolLiteral node) {
    enterTreeNode(node);
    if (afterConst && !inUnevaluatedConstant) {
      problem(node, "Symbol literal.");
    }
    exitTreeNode(node);
  }

  @override
  void visitContinueSwitchStatement(ContinueSwitchStatement node) {
    enterTreeNode(node);
    if (node.target.parent == null) {
      problem(node, "Target has no parent.");
    } else {
      SwitchStatement statement = node.target.parent as SwitchStatement;
      for (SwitchCase switchCase in statement.cases) {
        if (switchCase == node.target) {
          exitTreeNode(node);
          return;
        }
      }
      problem(node, "Switch case isn't child of parent.");
    }
    exitTreeNode(node);
  }

  @override
  void visitInstanceConstant(InstanceConstant constant) {
    constant.visitChildren(this);
    if (constant.typeArguments.length !=
        constant.classNode.typeParameters.length) {
      problem(
        currentParent,
        "Constant $constant provides ${constant.typeArguments.length}"
        " type arguments, but the class declares"
        " ${constant.classNode.typeParameters.length} parameters.",
      );
    }
    Set<Class> superClasses = <Class>{};
    int fieldCount = 0;
    for (Class? cls = constant.classNode; cls != null; cls = cls.superclass) {
      superClasses.add(cls);
      for (Field f in cls.fields) {
        if (!f.isStatic && !f.isConst) fieldCount++;
      }
    }
    if (constant.fieldValues.length != fieldCount) {
      problem(
        currentParent,
        "Constant $constant provides ${constant.fieldValues.length}"
        " field values, but the class declares"
        " $fieldCount fields.",
      );
    }
    for (Reference fieldRef in constant.fieldValues.keys) {
      Field field = fieldRef.asField;
      if (!superClasses.contains(field.enclosingClass)) {
        problem(
          currentParent,
          "Constant $constant refers to field $field,"
          " which does not belong to the right class.",
        );
      }
    }
  }

  @override
  void visitUnevaluatedConstant(UnevaluatedConstant constant) {
    bool savedInUnevaluatedConstant = inUnevaluatedConstant;
    inUnevaluatedConstant = true;
    TreeNode? oldParent = currentParent;
    currentParent = null;
    constant.expression.accept(this);
    currentParent = oldParent;
    inUnevaluatedConstant = savedInUnevaluatedConstant;
  }

  @override
  void defaultMemberReference(Member node) {
    if (!_membersSeenByVerifier.contains(node)) {
      problem(
        node,
        "Dangling reference to '$node', parent is: '${node.parent}'.",
      );
    }
  }

  @override
  void visitClassReference(Class node) {
    if (!classes.contains(node)) {
      problem(
        node,
        "Dangling reference to '$node', parent is: '${node.parent}'.",
      );
    }
  }

  @override
  void visitTypedefReference(Typedef node) {
    if (!typedefs.contains(node)) {
      problem(
        node,
        "Dangling reference to '$node', parent is: '${node.parent}'",
      );
    }
  }

  @override
  void visitTypeParameterType(TypeParameterType node) {
    TypeParameter parameter = node.parameter;
    GenericDeclaration? declaration = parameter.declaration;
    if (!typeParametersInScope.contains(parameter)) {
      problem(
        currentParent,
        "Type parameter '$parameter' referenced out of"
        " scope, declaration is: '${declaration}'.",
      );
    }
    if (declaration is Class && !classTypeParametersAreInScope) {
      problem(
        currentParent,
        "Type parameter '$parameter' referenced from"
        " static context, declaration is: '${declaration}'.",
      );
    }
    defaultDartType(node);
  }

  @override
  void visitInterfaceType(InterfaceType node) {
    if (isNullType(node) && node.nullability != Nullability.nullable) {
      problem(localContext, "Found a not nullable Null type: ${node}");
    }
    defaultDartType(node);
    if (node.typeArguments.length != node.classNode.typeParameters.length) {
      problem(
        currentParent,
        "Type $node provides ${node.typeArguments.length}"
        " type arguments, but the class declares"
        " ${node.classNode.typeParameters.length} parameters.",
      );
    }
    if (node.classNode.isAnonymousMixin) {
      bool isOk = false;
      if (currentParent is FunctionNode) {
        TreeNode? functionNodeParent = currentParent!.parent;
        if (functionNodeParent is Constructor) {
          if (functionNodeParent.parent == node.classNode) {
            // We only allow references to anonymous mixins in types as the
            // return type of its own constructor.
            isOk = true;
          }
        }
      }
      if (!isOk) {
        problem(
          currentParent,
          "Type $node references an anonymous mixin class.",
        );
      }
    }
  }

  @override
  void visitTypedefType(TypedefType node) {
    checkTypedef(node.typedefNode);
    defaultDartType(node);
    if (node.typeArguments.length != node.typedefNode.typeParameters.length) {
      problem(
        currentParent,
        "The typedef type $node provides ${node.typeArguments.length}"
        " type arguments, but the typedef declares"
        " ${node.typedefNode.typeParameters.length} parameters.",
      );
    }
  }

  @override
  void visitConstantExpression(ConstantExpression node) {
    enterTreeNode(node);
    inTreeNode(node, () {
      bool oldInConstant = inConstant;
      node.type.accept(this);
      // Only visit the [Constant] in constant context.
      inConstant = true;
      node.constant.accept(this);
      inConstant = oldInConstant;
    });
    exitTreeNode(node);
  }

  @override
  void visitTypeParameter(TypeParameter node) {
    if (identical(node.bound, TypeParameter.unsetBoundSentinel)) {
      problem(node, "Unset bound on type parameter $node");
    }
    if (identical(node.defaultType, TypeParameter.unsetDefaultTypeSentinel)) {
      problem(node, "Unset default type on type parameter $node");
    }
    // ignore: deprecated_member_use_from_same_package
    if (node.parent == null) {
      // TODO(johnniwinther): Enable this check.
      // problem(node, "Type parameter without parent: $node");
      node.visitChildren(this);
    } else {
      visitChildren(node);
    }
  }

  @override
  void visitTypedefTearOffConstant(TypedefTearOffConstant node) {
    _checkTypedefTearOff(node);
    declareStructuralParameters(node.parameters);
    super.visitTypedefTearOffConstant(node);
    undeclareStructuralParameters(node.parameters);
  }

  void _checkInterfaceTarget(Expression node, Member interfaceTarget) {
    if (!interfaceTarget.isInstanceMember) {
      problem(
        node,
        "Interface target $interfaceTarget is not an instance member.",
      );
    }
    if (interfaceTarget is Procedure &&
        interfaceTarget.stubKind == ProcedureStubKind.RepresentationField) {
      problem(
        node,
        "Representation field used as interface target: $interfaceTarget.",
      );
    }
    if (interfaceTarget.enclosingClass == null) {
      problem(
        node,
        "Interface target $interfaceTarget does not have an "
        "enclosing class.",
      );
    }
  }

  @override
  void visitInstanceInvocation(InstanceInvocation node) {
    if (node.name != node.interfaceTarget.name) {
      problem(
        node,
        "Instance invocation with name '${node.name}' has a "
        "target with name '${node.interfaceTarget.name}'.",
      );
    }
    _checkInterfaceTarget(node, node.interfaceTarget);
    super.visitInstanceInvocation(node);
  }

  @override
  void visitInstanceGet(InstanceGet node) {
    if (node.name != node.interfaceTarget.name) {
      problem(
        node,
        "Instance get with name '${node.name}' has a "
        "target with name '${node.interfaceTarget.name}'.",
      );
    }
    _checkInterfaceTarget(node, node.interfaceTarget);
    super.visitInstanceGet(node);
  }

  @override
  void visitInstanceTearOff(InstanceTearOff node) {
    if (node.name != node.interfaceTarget.name) {
      problem(
        node,
        "Instance tear-off with name '${node.name}' has a "
        "target with name '${node.interfaceTarget.name}'.",
      );
    }
    _checkInterfaceTarget(node, node.interfaceTarget);
    super.visitInstanceTearOff(node);
  }

  @override
  void visitInstanceSet(InstanceSet node) {
    if (node.name != node.interfaceTarget.name) {
      problem(
        node,
        "Instance set with name '${node.name}' has a "
        "target with name '${node.interfaceTarget.name}'.",
      );
    }
    _checkInterfaceTarget(node, node.interfaceTarget);
    super.visitInstanceSet(node);
  }

  /// Invoked by all visit methods if the visited node is a [TreeNode].
  // TODO(johnniwinther): Merge this with enter/exitParent.
  void enterTreeNode(TreeNode node) {
    treeNodeStack.add(node);
    testLocation(node);
  }

  /// Invoked by all visit methods if the visited node is a [TreeNode].
  void exitTreeNode(TreeNode node) {
    if (treeNodeStack.isEmpty) {
      throw new StateError(
        "Attempting to exit tree node '${node}' "
        "when the tree node stack is empty.",
      );
    }
    if (!identical(treeNodeStack.last, node)) {
      throw new StateError(
        "Attempting to exit tree node '${node}' "
        "when another node '${treeNodeStack.last}' is active.",
      );
    }
    treeNodeStack.removeLast();
  }

  TreeNode? getLastSeenTreeNode({bool withLocation = false}) {
    assert(treeNodeStack.isNotEmpty);
    for (int i = treeNodeStack.length - 1; i >= 0; --i) {
      TreeNode node = treeNodeStack[i];
      if (withLocation && !_hasLocation(_getLocation(node), node)) continue;
      return node;
    }
    return null;
  }

  TreeNode? getSameLibraryLastSeenTreeNode({bool withLocation = false}) {
    if (treeNodeStack.isEmpty) return null;
    if (currentLibrary == null) return null;

    for (int i = treeNodeStack.length - 1; i >= 0; --i) {
      TreeNode node = treeNodeStack[i];
      Location? location = _getLocation(node);
      if (withLocation && !_hasLocation(location, node)) continue;
      if (location != null && location.file == currentLibrary!.fileUri) {
        return node;
      }
    }
    return null;
  }

  /// Returns the `TreeNode.location` while handling [RangeError]s caused by
  /// file offsets not within the range of the enclosing file.
  Location? _getLocation(TreeNode node, {bool allowInvalidLocation = false}) {
    try {
      return node.location;
    } on RangeError catch (e) {
      if (allowInvalidLocation ||
          target.verification.allowInvalidLocation(stage, node)) {
        return null;
      }
      problem(
        node,
        "Invalid location with target '${target.name}' on "
        "${node} (${node.runtimeType}): $e",
      );
    }
    return null;
  }

  bool _hasLocation(Location? location, TreeNode node) {
    return location != null && node.fileOffset != TreeNode.noOffset;
  }

  bool _isInSameLibrary(Library? library, TreeNode node) {
    if (library == null) return false;
    Location? location = _getLocation(node);
    if (location == null) return false;
    return library.fileUri == location.file;
  }

  TreeNode? get localContext {
    TreeNode? result = getSameLibraryLastSeenTreeNode(withLocation: true);
    if (result == null &&
        currentClassOrExtensionOrMember != null &&
        _isInSameLibrary(currentLibrary, currentClassOrExtensionOrMember!)) {
      result = currentClassOrExtensionOrMember;
    }
    return result;
  }

  TreeNode? get remoteContext {
    TreeNode? result = getLastSeenTreeNode(withLocation: true);
    if (result != null && _isInSameLibrary(currentLibrary, result)) {
      result = null;
    }
    return result;
  }

  // We disable the location test for now, at least these tests currently fail:
  //  outline/dartdevc/factory_patch/main
  //  outline/general/constructor_patch/main
  //  outline/general/factory_patch/main
  //  outline/general/mixin_from_patch/main
  //  outline/general/multiple_class_patches/main
  //  outline/general/patch_extends_implements/main
  //  outline/nnbd/platform_optional_parameters/main
  static const bool doTestLocation = false;

  void testLocation(TreeNode node) {
    if (!doTestLocation) return;
    // When these comes from patching (and in the future from augmentation) they
    // don't point correctly.
    if (node is LibraryDependency || node is LibraryPart) return;
    try {
      if (node.fileOffset != TreeNode.noOffset) {
        node.location;
      }
    } catch (e) {
      problem(
        node,
        "${node.runtimeType} crashes when  asked for location: '$e'",
        context: node,
      );
    }
  }

  Uri checkLocation(TreeNode node, String? name, Uri fileUri) {
    if (name == null || name.contains("#")) {
      // TODO(ahe): Investigate if these checks can be enabled:
      // if (node.fileUri != null && node is! Library) {
      //   problem(node, "A synthetic node shouldn't have a fileUri",
      //       context: node);
      // }
      // if (node.fileOffset != -1) {
      //   problem(node, "A synthetic node shouldn't have a fileOffset",
      //       context: node);
      // }
      return fileUri;
    } else {
      if (node.fileOffset == TreeNode.noOffset &&
          !target.verification.allowNoFileOffset(stage, node)) {
        problem(node, "'$name' has no fileOffset", context: node);
      }
      return fileUri;
    }
  }

  void checkSuperInvocation(TreeNode node) {
    Member? containingMember = getContainingMember(node);
    if (containingMember == null) {
      problem(node, 'Super call outside of any member');
    } else {
      if (!containingMember.containsSuperCalls) {
        problem(
          node,
          'Super call in a member lacking TransformerFlag.superCalls',
        );
      }
    }
  }

  Member? getContainingMember(TreeNode? node) {
    while (node != null) {
      if (node is Member) return node;
      node = node.parent;
    }
    return null;
  }

  @override
  void visitAsExpression(AsExpression node) {
    enterTreeNode(node);
    super.visitAsExpression(node);
    if (node.fileOffset == TreeNode.noOffset &&
        !node.isUnchecked &&
        !target.verification.allowNoFileOffset(stage, node)) {
      TreeNode? parent = node.parent;
      while (parent != null) {
        if (parent.fileOffset != TreeNode.noOffset) break;
        parent = parent.parent;
      }
      problem(parent, "No offset for $node", context: node);
    }
    exitTreeNode(node);
  }

  @override
  void visitExpressionStatement(ExpressionStatement node) {
    // Bypass verification of the [StaticGet] in [RedirectingFactoryBody] as
    // this is a static get without a getter.
    enterTreeNode(node);
    super.visitExpressionStatement(node);
    exitTreeNode(node);
  }

  bool isNullType(DartType node) => node is NullType;

  bool isObjectClass(Class c) {
    return c.name == "Object" &&
        c.enclosingLibrary.importUri.isScheme("dart") &&
        c.enclosingLibrary.importUri.path == "core";
  }

  bool isTopType(DartType node) {
    return node is DynamicType ||
        node is VoidType ||
        node is InterfaceType &&
            isObjectClass(node.classNode) &&
            node.nullability == Nullability.nullable ||
        node is FutureOrType && isTopType(node.typeArgument);
  }

  bool isFutureOrNull(DartType node) {
    return isNullType(node) ||
        node is FutureOrType && isFutureOrNull(node.typeArgument);
  }

  @override
  void defaultDartType(DartType node) {
    if (!AllowedTypes.isAllowed(node, inConstant: inConstant)) {
      final TreeNode? localContext = this.localContext;
      final TreeNode? remoteContext = this.remoteContext;
      problem(
        localContext,
        "Unexpected appearance of the disallowed type $node"
        "${inConstant ? " inside a constant" : ""}.",
        origin: remoteContext,
      );
    }
    super.defaultDartType(node);
  }

  @override
  void visitSuperMethodInvocation(SuperMethodInvocation node) {
    enterTreeNode(node);
    checkSuperInvocation(node);
    super.visitSuperMethodInvocation(node);
    exitTreeNode(node);
  }

  @override
  void visitSuperPropertyGet(SuperPropertyGet node) {
    enterTreeNode(node);
    checkSuperInvocation(node);
    super.visitSuperPropertyGet(node);
    exitTreeNode(node);
  }

  @override
  void visitSuperPropertySet(SuperPropertySet node) {
    enterTreeNode(node);
    checkSuperInvocation(node);
    super.visitSuperPropertySet(node);
    exitTreeNode(node);
  }

  void _checkConstructorTearOff(Node node, Member tearOffTarget) {
    if (tearOffTarget.enclosingLibrary.importUri.isScheme('dart')) {
      // Platform libraries are not compilation with test flags and might
      // contain tear-offs not expected when testing lowerings.
      return;
    }
    if (tearOffTarget is Constructor &&
        target.isConstructorTearOffLoweringEnabled) {
      problem(
        node is TreeNode ? node : getLastSeenTreeNode(),
        '${node.runtimeType} nodes for generative constructors should be '
        'lowered for target "${target.name}".',
      );
    }
    if (tearOffTarget is Procedure &&
        tearOffTarget.isFactory &&
        target.isFactoryTearOffLoweringEnabled) {
      problem(
        node is TreeNode ? node : getLastSeenTreeNode(),
        '${node.runtimeType} nodes for factory constructors should be '
        'lowered for target "${target.name}".',
      );
    }
  }

  @override
  void visitConstructorTearOff(ConstructorTearOff node) {
    _checkConstructorTearOff(node, node.target);
    super.visitConstructorTearOff(node);
  }

  @override
  void visitConstructorTearOffConstant(ConstructorTearOffConstant node) {
    _checkConstructorTearOff(node, node.target);
    super.visitConstructorTearOffConstant(node);
  }

  void _checkTypedefTearOff(Node node) {
    if (target.isTypedefTearOffLoweringEnabled) {
      problem(
        node is TreeNode ? node : getLastSeenTreeNode(),
        '${node.runtimeType} nodes for typedefs should be '
        'lowered for target "${target.name}".',
      );
    }
  }

  void _checkRedirectingFactoryTearOff(Node node) {
    if (target.isRedirectingFactoryTearOffLoweringEnabled) {
      problem(
        node is TreeNode ? node : getLastSeenTreeNode(),
        'ConstructorTearOff nodes for redirecting factories should be '
        'lowered for target "${target.name}".',
      );
    }
  }

  @override
  void visitRedirectingFactoryTearOff(RedirectingFactoryTearOff node) {
    enterScopeProvider(node.function);
    _checkRedirectingFactoryTearOff(node);
    super.visitRedirectingFactoryTearOff(node);
    exitScopeProvider(node.function);
  }

  @override
  void visitRedirectingFactoryTearOffConstant(
    RedirectingFactoryTearOffConstant node,
  ) {
    enterScopeProvider(node.function);
    _checkRedirectingFactoryTearOff(node);
    super.visitRedirectingFactoryTearOffConstant(node);
    exitScopeProvider(node.function);
  }

  @override
  void visitSwitchStatement(SwitchStatement node) {
    if (node.expressionTypeInternal == null) {
      problem(node, 'SwitchStatement.expressionType has not been set.');
    }
    super.visitSwitchStatement(node);
  }

  @override
  void visitListConcatenation(ListConcatenation node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      if (!inUnevaluatedConstant) {
        problem(node, "Unexpected internal node $node.");
      }
    }
  }

  @override
  void visitSetConcatenation(SetConcatenation node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      if (!inUnevaluatedConstant) {
        problem(node, "Unexpected internal node $node.");
      }
    }
  }

  @override
  void visitMapConcatenation(MapConcatenation node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      if (!inUnevaluatedConstant) {
        problem(node, "Unexpected internal node $node.");
      }
    }
  }

  @override
  void visitInstanceCreation(InstanceCreation node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      if (!inUnevaluatedConstant) {
        problem(node, "Unexpected internal node $node.");
      }
    }
  }

  @override
  void visitFileUriExpression(FileUriExpression node) {
    if (!target.supportsFileUriExpression) {
      if (stage >= VerificationStage.afterConstantEvaluation) {
        if (!inUnevaluatedConstant) {
          problem(node, "Unexpected internal node $node.");
        }
      }
    }
  }

  @override
  void visitPatternAssignment(PatternAssignment node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      problem(node, "Unexpected internal node $node.");
    }
  }

  @override
  void visitPatternVariableDeclaration(PatternVariableDeclaration node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      problem(node, "Unexpected internal node $node.");
    }
  }

  @override
  void visitIfCaseStatement(IfCaseStatement node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      problem(node, "Unexpected internal node $node.");
    }
  }

  @override
  void visitPatternSwitchStatement(PatternSwitchStatement node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      problem(node, "Unexpected internal node $node.");
    }
  }

  @override
  void defaultPattern(Pattern node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      problem(node, "Unexpected internal node $node.");
    }
  }

  @override
  void visitSwitchExpression(SwitchExpression node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      problem(node, "Unexpected internal node $node.");
    }
  }

  @override
  void visitSwitchExpressionCase(SwitchExpressionCase node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      problem(node, "Unexpected internal node $node.");
    }
  }

  @override
  void visitPatternGuard(PatternGuard node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      problem(node, "Unexpected internal node $node.");
    }
  }

  @override
  void visitPatternSwitchCase(PatternSwitchCase node) {
    if (stage >= VerificationStage.afterConstantEvaluation) {
      problem(node, "Unexpected internal node $node.");
    }
  }
}

class StaticTypeError {
  TreeNode context;
  String message;

  new({required this.context, required this.message});
}

class VerifyGetStaticType extends RecursiveVisitor {
  final TypeEnvironment env;
  Member? currentMember;
  final StatefulStaticTypeContext _staticTypeContext;
  final List<StaticTypeError> errors = [];

  new(this.env)
    : _staticTypeContext = new StatefulStaticTypeContext.stacked(env);

  @override
  void visitLibrary(Library node) {
    _staticTypeContext.enterLibrary(node);
    super.visitLibrary(node);
    _staticTypeContext.leaveLibrary(node);
  }

  @override
  void visitField(Field node) {
    currentMember = node;
    _staticTypeContext.enterMember(node);
    super.visitField(node);
    _staticTypeContext.leaveMember(node);
    currentMember = node;
  }

  @override
  void visitProcedure(Procedure node) {
    currentMember = node;
    _staticTypeContext.enterMember(node);
    super.visitProcedure(node);
    _staticTypeContext.leaveMember(node);
    currentMember = node;
  }

  @override
  void visitConstructor(Constructor node) {
    currentMember = node;
    _staticTypeContext.enterMember(node);
    super.visitConstructor(node);
    _staticTypeContext.leaveMember(node);
    currentMember = null;
  }

  @override
  void visitLet(Let node) {
    if (_isCompileTimeErrorEncoding(node)) return;
    super.visitLet(node);
  }

  @override
  void visitAsExpression(AsExpression node) {
    if (node.isCovarianceCheck &&
        node.operand.getStaticType(_staticTypeContext) == node.type) {
      String message =
          "The operand of the as-check with isCovarianceCheck flag set has the "
          "same static type as the target type of the check. "
          "Operand node kind is '${node.operand.runtimeType}'. Target check "
          "type is '${node.type}'.";
      errors.add(new StaticTypeError(context: node, message: message));
      // TODO(cstefantsova): Make sure the 'errors' are reported, then remove
      // the throw statement below.
      throw message;
    }
  }

  @override
  void visitInvalidExpression(InvalidExpression node) {
    return;
  }

  @override
  void defaultExpression(Expression node) {
    try {
      node.getStaticType(_staticTypeContext);
    } catch (_) {
      print(
        'Error in $currentMember in ${currentMember?.fileUri}: '
        '$node (${node.runtimeType})',
      );
      rethrow;
    }
    super.defaultExpression(node);
  }
}

void checkInitializers(Constructor constructor) {
  // TODO(ahe): I'll add more here in other CLs.
}

bool _isCompileTimeErrorEncoding(TreeNode? node) {
  return node is Let && node.value is InvalidExpression;
}

class AllowedTypes implements DartTypeVisitor<bool> {
  static bool isAllowed(DartType type, {required bool inConstant}) {
    return type.accept(
      inConstant
          ? const AllowedTypes(inConstant: true)
          : const AllowedTypes(inConstant: false),
    );
  }

  final bool inConstant;

  const new({required this.inConstant});

  @override
  bool visitAuxiliaryType(AuxiliaryType node) => false;

  @override
  bool visitDynamicType(DynamicType node) => true;

  @override
  bool visitFunctionType(FunctionType node) => true;

  @override
  bool visitFutureOrType(FutureOrType node) => true;

  @override
  bool visitExtensionType(ExtensionType node) => !inConstant;

  @override
  bool visitInterfaceType(InterfaceType node) => true;

  @override
  bool visitIntersectionType(IntersectionType node) => true;

  @override
  bool visitInvalidType(InvalidType node) => true;

  @override
  bool visitNeverType(NeverType node) => true;

  @override
  bool visitNullType(NullType node) => true;

  @override
  bool visitRecordType(RecordType node) => true;

  @override
  bool visitTypeParameterType(TypeParameterType node) => true;

  @override
  bool visitStructuralParameterType(StructuralParameterType node) => true;

  @override
  bool visitTypedefType(TypedefType node) => true;

  @override
  bool visitVoidType(VoidType node) => true;

  @override
  bool visitFunctionTypeParameterType(FunctionTypeParameterType node) {
    // TODO(cstefantsova): Implement visitFunctionTypeParameterType.
    throw new UnimplementedError(
      "Unimplemented support for $node (${node.runtimeType}).",
    );
  }

  @override
  bool visitClassTypeParameterType(ClassTypeParameterType node) {
    // TODO(cstefantsova): Implement visitClassTypeParameterType.
    throw new UnimplementedError(
      "Unimplemented support for $node (${node.runtimeType}).",
    );
  }
}