// 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.class_builder;

import 'package:kernel/ast.dart'
    show
        Class,
        Constructor,
        DartType,
        DynamicType,
        FunctionNode,
        FunctionType,
        FutureOrType,
        InterfaceType,
        Member,
        Name,
        NullType,
        Nullability,
        Supertype,
        TreeNode,
        TypeParameter,
        getAsTypeArguments;
import 'package:kernel/class_hierarchy.dart'
    show ClassHierarchy, ClassHierarchyMembers;
import 'package:kernel/core_types.dart' show CoreTypes;
import 'package:kernel/src/legacy_erasure.dart';
import 'package:kernel/text/text_serialization_verifier.dart';
import 'package:kernel/type_algebra.dart' show Substitution, substitute;
import 'package:kernel/type_environment.dart'
    show SubtypeCheckMode, TypeEnvironment;

import '../fasta_codes.dart';
import '../kernel/kernel_helper.dart';
import '../kernel/redirecting_factory_body.dart' show RedirectingFactoryBody;
import '../loader.dart';
import '../modifier.dart';
import '../names.dart' show noSuchMethodName;
import '../problems.dart' show internalProblem, unhandled;
import '../scope.dart';
import '../source/source_factory_builder.dart';
import '../source/source_library_builder.dart' show SourceLibraryBuilder;
import '../source/source_loader.dart';
import '../source/source_member_builder.dart';
import '../type_inference/type_schema.dart' show UnknownType;
import '../util/helpers.dart' show DelayedActionPerformer;
import 'builder.dart';
import 'constructor_reference_builder.dart';
import 'declaration_builder.dart';
import 'function_builder.dart';
import 'library_builder.dart';
import 'member_builder.dart';
import 'metadata_builder.dart';
import 'named_type_builder.dart';
import 'never_type_declaration_builder.dart';
import 'nullability_builder.dart';
import 'type_alias_builder.dart';
import 'type_builder.dart';
import 'type_declaration_builder.dart';
import 'type_variable_builder.dart';
import 'void_type_declaration_builder.dart';

abstract class ClassBuilder implements DeclarationBuilder {
  /// The type variables declared on a class, extension or mixin declaration.
  List<TypeVariableBuilder>? get typeVariables;

  /// The type in the `extends` clause of a class declaration.
  ///
  /// Currently this also holds the synthesized super class for a mixin
  /// declaration.
  abstract TypeBuilder? supertypeBuilder;

  /// The type in the `implements` clause of a class or mixin declaration.
  abstract List<TypeBuilder>? interfaceBuilders;

  /// The types in the `on` clause of an extension or mixin declaration.
  List<TypeBuilder>? get onTypes;

  ConstructorScope get constructors;

  ConstructorScopeBuilder get constructorScopeBuilder;

  abstract ClassBuilder? actualOrigin;

  @override
  Uri get fileUri;

  bool get isAbstract;

  bool get isMacro;

  bool get declaresConstConstructor;

  bool get isMixin;

  bool get isMixinApplication;

  bool get isAnonymousMixinApplication;

  abstract TypeBuilder? mixedInTypeBuilder;

  void buildOutlineExpressions(
      SourceLibraryBuilder library,
      ClassHierarchy classHierarchy,
      List<DelayedActionPerformer> delayedActionPerformers,
      List<SynthesizedFunctionNode> synthesizedFunctionNodes);

  /// Registers a constructor redirection for this class and returns true if
  /// this redirection gives rise to a cycle that has not been reported before.
  bool checkConstructorCyclic(String source, String target);

  MemberBuilder? findConstructorOrFactory(
      String name, int charOffset, Uri uri, LibraryBuilder accessingLibrary);

  void forEach(void f(String name, Builder builder));

  /// The [Class] built by this builder.
  ///
  /// For a patch class the origin class is returned.
  Class get cls;

  @override
  ClassBuilder get origin;

  Class get actualCls;

  abstract bool isNullClass;

  @override
  InterfaceType get thisType;

  InterfaceType get legacyRawType;

  InterfaceType get nullableRawType;

  InterfaceType get nonNullableRawType;

  InterfaceType rawType(Nullability nullability);

  List<DartType> buildTypeArguments(
      LibraryBuilder library, List<TypeBuilder>? arguments);

  Supertype buildSupertype(
      LibraryBuilder library, List<TypeBuilder>? arguments);

  Supertype buildMixedInType(
      LibraryBuilder library, List<TypeBuilder>? arguments);

  void checkSupertypes(CoreTypes coreTypes);

  void handleSeenCovariant(
      ClassHierarchyMembers memberHierarchy,
      Member interfaceMember,
      bool isSetter,
      callback(Member interfaceMember, bool isSetter));

  bool hasUserDefinedNoSuchMethod(
      Class klass, ClassHierarchy hierarchy, Class objectClass);

  void checkMixinApplication(ClassHierarchy hierarchy, CoreTypes coreTypes);

  // Computes the function type of a given redirection target. Returns [null] if
  // the type of the target could not be computed.
  FunctionType? computeRedirecteeType(
      RedirectingFactoryBuilder factory, TypeEnvironment typeEnvironment);

  String computeRedirecteeName(ConstructorReferenceBuilder redirectionTarget);

  void checkRedirectingFactory(
      RedirectingFactoryBuilder factory, TypeEnvironment typeEnvironment);

  void checkRedirectingFactories(TypeEnvironment typeEnvironment);

  /// Returns a map which maps the type variables of [superclass] to their
  /// respective values as defined by the superclass clause of this class (and
  /// its superclasses).
  ///
  /// It's assumed that [superclass] is a superclass of this class.
  ///
  /// For example, given:
  ///
  ///     class Box<T> {}
  ///     class BeatBox extends Box<Beat> {}
  ///     class Beat {}
  ///
  /// We have:
  ///
  ///     [[BeatBox]].getSubstitutionMap([[Box]]) -> {[[Box::T]]: Beat]]}.
  ///
  /// It's an error if [superclass] isn't a superclass.
  Map<TypeParameter, DartType> getSubstitutionMap(Class superclass);

  /// Looks up the member by [name] on the class built by this class builder.
  ///
  /// If [isSetter] is `false`, only fields, methods, and getters with that name
  /// will be found.  If [isSetter] is `true`, only non-final fields and setters
  /// will be found.
  ///
  /// If [isSuper] is `false`, the member is found among the interface members
  /// the class built by this class builder. If [isSuper] is `true`, the member
  /// is found among the class members of the superclass.
  ///
  /// If this class builder is a patch, interface members declared in this
  /// patch are searched before searching the interface members in the origin
  /// class.
  Member? lookupInstanceMember(ClassHierarchy hierarchy, Name name,
      {bool isSetter: false, bool isSuper: false});

  /// Looks up the constructor by [name] on the class built by this class
  /// builder.
  ///
  /// If [isSuper] is `true`, constructors in the superclass are searched.
  Constructor? lookupConstructor(Name name, {bool isSuper: false});

  /// Calls [f] for each constructor declared in this class.
  ///
  /// If [includeInjectedConstructors] is `true`, constructors only declared in
  /// the patch class, if any, are included.
  void forEachConstructor(void Function(String, MemberBuilder) f,
      {bool includeInjectedConstructors: false});
}

abstract class ClassBuilderImpl extends DeclarationBuilderImpl
    implements ClassBuilder {
  @override
  List<TypeVariableBuilder>? typeVariables;

  @override
  TypeBuilder? supertypeBuilder;

  @override
  List<TypeBuilder>? interfaceBuilders;

  @override
  List<TypeBuilder>? onTypes;

  @override
  final ConstructorScope constructors;

  @override
  final ConstructorScopeBuilder constructorScopeBuilder;

  Map<String, ConstructorRedirection>? _redirectingConstructors;

  @override
  ClassBuilder? actualOrigin;

  @override
  bool isNullClass = false;

  InterfaceType? _legacyRawType;
  InterfaceType? _nullableRawType;
  InterfaceType? _nonNullableRawType;
  InterfaceType? _thisType;

  ClassBuilderImpl(
      List<MetadataBuilder>? metadata,
      int modifiers,
      String name,
      this.typeVariables,
      this.supertypeBuilder,
      this.interfaceBuilders,
      this.onTypes,
      Scope scope,
      this.constructors,
      LibraryBuilder parent,
      int charOffset)
      : constructorScopeBuilder = new ConstructorScopeBuilder(constructors),
        super(metadata, modifiers, name, parent, charOffset, scope);

  @override
  String get debugName => "ClassBuilder";

  @override
  bool get isAbstract => (modifiers & abstractMask) != 0;

  @override
  bool get isMixin => (modifiers & mixinDeclarationMask) != 0;

  @override
  bool get isMixinApplication => mixedInTypeBuilder != null;

  @override
  bool get isNamedMixinApplication {
    return isMixinApplication && (modifiers & namedMixinApplicationMask) != 0;
  }

  @override
  bool get isAnonymousMixinApplication {
    return isMixinApplication && !isNamedMixinApplication;
  }

  @override
  bool get declaresConstConstructor =>
      (modifiers & declaresConstConstructorMask) != 0;

  @override
  void forEachConstructor(void Function(String, MemberBuilder) f,
      {bool includeInjectedConstructors: false}) {
    if (isPatch) {
      actualOrigin!.forEachConstructor(f,
          includeInjectedConstructors: includeInjectedConstructors);
    } else {
      constructors.forEach(f);
    }
  }

  @override
  void buildOutlineExpressions(
      SourceLibraryBuilder library,
      ClassHierarchy classHierarchy,
      List<DelayedActionPerformer> delayedActionPerformers,
      List<SynthesizedFunctionNode> synthesizedFunctionNodes) {
    void build(String ignore, Builder declaration) {
      SourceMemberBuilder member = declaration as SourceMemberBuilder;
      member.buildOutlineExpressions(library, classHierarchy,
          delayedActionPerformers, synthesizedFunctionNodes);
    }

    MetadataBuilder.buildAnnotations(isPatch ? origin.cls : cls, metadata,
        library, this, null, fileUri, library.scope);
    if (typeVariables != null) {
      for (int i = 0; i < typeVariables!.length; i++) {
        typeVariables![i].buildOutlineExpressions(library, this, null,
            classHierarchy, delayedActionPerformers, scope.parent!);
      }
    }

    constructors.forEach(build);
    scope.forEach(build);
  }

  /// Registers a constructor redirection for this class and returns true if
  /// this redirection gives rise to a cycle that has not been reported before.
  @override
  bool checkConstructorCyclic(String source, String target) {
    ConstructorRedirection? redirect = new ConstructorRedirection(target);
    _redirectingConstructors ??= <String, ConstructorRedirection>{};
    _redirectingConstructors![source] = redirect;
    while (redirect != null) {
      if (redirect.cycleReported) return false;
      if (redirect.target == source) {
        redirect.cycleReported = true;
        return true;
      }
      redirect = _redirectingConstructors![redirect.target];
    }
    return false;
  }

  @override
  Builder? findStaticBuilder(
      String name, int charOffset, Uri fileUri, LibraryBuilder accessingLibrary,
      {bool isSetter: false}) {
    if (accessingLibrary.nameOriginBuilder.origin !=
            library.nameOriginBuilder.origin &&
        name.startsWith("_")) {
      return null;
    }
    Builder? declaration = isSetter
        ? scope.lookupSetter(name, charOffset, fileUri, isInstanceScope: false)
        : scope.lookup(name, charOffset, fileUri, isInstanceScope: false);
    if (declaration == null && isPatch) {
      return origin.findStaticBuilder(
          name, charOffset, fileUri, accessingLibrary,
          isSetter: isSetter);
    }
    return declaration;
  }

  @override
  MemberBuilder? findConstructorOrFactory(
      String name, int charOffset, Uri uri, LibraryBuilder accessingLibrary) {
    if (accessingLibrary.nameOriginBuilder.origin !=
            library.nameOriginBuilder.origin &&
        name.startsWith("_")) {
      return null;
    }
    MemberBuilder? declaration =
        constructors.lookup(name == 'new' ? '' : name, charOffset, uri);
    if (declaration == null && isPatch) {
      return origin.findConstructorOrFactory(
          name, charOffset, uri, accessingLibrary);
    }
    return declaration;
  }

  @override
  void forEach(void f(String name, Builder builder)) {
    scope.forEach(f);
  }

  @override
  Builder? lookupLocalMember(String name,
      {bool setter: false, bool required: false}) {
    Builder? builder = scope.lookupLocalMember(name, setter: setter);
    if (builder == null && isPatch) {
      builder = origin.scope.lookupLocalMember(name, setter: setter);
    }
    if (required && builder == null) {
      internalProblem(
          templateInternalProblemNotFoundIn.withArguments(
              name, fullNameForErrors),
          -1,
          null);
    }
    return builder;
  }

  /// Find the first member of this class with [name]. This method isn't
  /// suitable for scope lookups as it will throw an error if the name isn't
  /// declared. The [scope] should be used for that. This method is used to
  /// find a member that is known to exist and it will pick the first
  /// declaration if the name is ambiguous.
  ///
  /// For example, this method is convenient for use when building synthetic
  /// members, such as those of an enum.
  MemberBuilder? firstMemberNamed(String name) {
    MemberBuilder declaration =
        lookupLocalMember(name, required: true) as MemberBuilder;
    while (declaration.next != null) {
      declaration = declaration.next as MemberBuilder;
    }
    return declaration;
  }

  @override
  ClassBuilder get origin => actualOrigin ?? this;

  @override
  InterfaceType get thisType {
    return _thisType ??= new InterfaceType(cls, library.nonNullable,
        getAsTypeArguments(cls.typeParameters, library.library));
  }

  @override
  InterfaceType get legacyRawType {
    return _legacyRawType ??= new InterfaceType(cls, Nullability.legacy,
        new List<DartType>.filled(typeVariablesCount, const DynamicType()));
  }

  @override
  InterfaceType get nullableRawType {
    return _nullableRawType ??= new InterfaceType(cls, Nullability.nullable,
        new List<DartType>.filled(typeVariablesCount, const DynamicType()));
  }

  @override
  InterfaceType get nonNullableRawType {
    return _nonNullableRawType ??= new InterfaceType(
        cls,
        Nullability.nonNullable,
        new List<DartType>.filled(typeVariablesCount, const DynamicType()));
  }

  @override
  InterfaceType rawType(Nullability nullability) {
    switch (nullability) {
      case Nullability.legacy:
        return legacyRawType;
      case Nullability.nullable:
        return nullableRawType;
      case Nullability.nonNullable:
        return nonNullableRawType;
      case Nullability.undetermined:
      default:
        return unhandled("$nullability", "rawType", noOffset, noUri);
    }
  }

  @override
  DartType buildTypeWithBuiltArguments(LibraryBuilder library,
      Nullability nullability, List<DartType>? arguments) {
    assert(arguments == null || cls.typeParameters.length == arguments.length);
    if (isNullClass) {
      return const NullType();
    }
    if (name == "FutureOr") {
      LibraryBuilder parentLibrary = parent as LibraryBuilder;
      if (parentLibrary.importUri.scheme == "dart" &&
          parentLibrary.importUri.path == "async") {
        assert(arguments != null && arguments.length == 1);
        return new FutureOrType(arguments!.single, nullability);
      }
    }
    return arguments == null
        ? rawType(nullability)
        : new InterfaceType(cls, nullability, arguments);
  }

  @override
  int get typeVariablesCount => typeVariables?.length ?? 0;

  @override
  List<DartType> buildTypeArguments(
      LibraryBuilder library, List<TypeBuilder>? arguments) {
    if (arguments == null && typeVariables == null) {
      return <DartType>[];
    }

    if (arguments == null && typeVariables != null) {
      List<DartType> result = new List<DartType>.generate(typeVariables!.length,
          (int i) => typeVariables![i].defaultType!.build(library),
          growable: true);
      if (library is SourceLibraryBuilder) {
        library.inferredTypes.addAll(result);
      }
      return result;
    }

    if (arguments != null && arguments.length != typeVariablesCount) {
      // That should be caught and reported as a compile-time error earlier.
      return unhandled(
          templateTypeArgumentMismatch
              .withArguments(typeVariablesCount)
              .problemMessage,
          "buildTypeArguments",
          -1,
          null);
    }

    assert(arguments!.length == typeVariablesCount);
    List<DartType> result = new List<DartType>.generate(
        arguments!.length, (int i) => arguments[i].build(library),
        growable: true);
    return result;
  }

  @override
  DartType buildType(LibraryBuilder library,
      NullabilityBuilder nullabilityBuilder, List<TypeBuilder>? arguments) {
    return buildTypeWithBuiltArguments(
        library,
        nullabilityBuilder.build(library),
        buildTypeArguments(library, arguments));
  }

  @override
  Supertype buildSupertype(
      LibraryBuilder library, List<TypeBuilder>? arguments) {
    Class cls = isPatch ? origin.cls : this.cls;
    List<DartType> typeArguments = buildTypeArguments(library, arguments);
    if (!library.isNonNullableByDefault) {
      for (int i = 0; i < typeArguments.length; ++i) {
        typeArguments[i] = legacyErasure(typeArguments[i]);
      }
    }
    return new Supertype(cls, typeArguments);
  }

  @override
  Supertype buildMixedInType(
      LibraryBuilder library, List<TypeBuilder>? arguments) {
    Class cls = isPatch ? origin.cls : this.cls;
    if (arguments != null) {
      return new Supertype(cls, buildTypeArguments(library, arguments));
    } else {
      return new Supertype(
          cls,
          new List<DartType>.filled(
              cls.typeParameters.length, const UnknownType(),
              growable: true));
    }
  }

  @override
  void checkSupertypes(CoreTypes coreTypes) {
    // This method determines whether the class (that's being built) its super
    // class appears both in 'extends' and 'implements' clauses and whether any
    // interface appears multiple times in the 'implements' clause.
    // Moreover, it checks that `FutureOr` and `void` are not among the
    // supertypes.

    void fail(NamedTypeBuilder target, Message message,
        TypeAliasBuilder? aliasBuilder) {
      int nameOffset = target.nameOffset;
      int nameLength = target.nameLength;
      // TODO(eernst): nameOffset not fully implemented; use backup.
      if (nameOffset == -1) {
        nameOffset = this.charOffset;
        nameLength = noLength;
      }
      if (aliasBuilder != null) {
        addProblem(message, nameOffset, nameLength, context: [
          messageTypedefCause.withLocation(
              aliasBuilder.fileUri, aliasBuilder.charOffset, noLength),
        ]);
      } else {
        addProblem(message, nameOffset, nameLength);
      }
    }

    // Extract and check superclass (if it exists).
    ClassBuilder? superClass;
    TypeBuilder? superClassType = supertypeBuilder;
    if (superClassType is NamedTypeBuilder) {
      TypeDeclarationBuilder? decl = superClassType.declaration;
      TypeAliasBuilder? aliasBuilder; // Non-null if a type alias is use.
      if (decl is TypeAliasBuilder) {
        aliasBuilder = decl;
        decl = aliasBuilder.unaliasDeclaration(superClassType.arguments,
            isUsedAsClass: true,
            usedAsClassCharOffset: superClassType.charOffset,
            usedAsClassFileUri: superClassType.fileUri);
      }
      // TODO(eernst): Should gather 'restricted supertype' checks in one place,
      // e.g., dynamic/int/String/Null and more are checked elsewhere.
      if (decl is VoidTypeDeclarationBuilder) {
        fail(superClassType, messageExtendsVoid, aliasBuilder);
      } else if (decl is NeverTypeDeclarationBuilder) {
        fail(superClassType, messageExtendsNever, aliasBuilder);
      } else if (decl is ClassBuilder) {
        superClass = decl;
      }
    }
    if (interfaceBuilders == null) return;

    // Validate interfaces.
    Map<ClassBuilder, int>? problems;
    Map<ClassBuilder, int>? problemsOffsets;
    Set<ClassBuilder> implemented = new Set<ClassBuilder>();
    for (TypeBuilder type in interfaceBuilders!) {
      if (type is NamedTypeBuilder) {
        int? charOffset = type.charOffset;
        TypeDeclarationBuilder? typeDeclaration = type.declaration;
        TypeDeclarationBuilder? decl;
        TypeAliasBuilder? aliasBuilder; // Non-null if a type alias is used.
        if (typeDeclaration is TypeAliasBuilder) {
          aliasBuilder = typeDeclaration;
          decl = aliasBuilder.unaliasDeclaration(type.arguments,
              isUsedAsClass: true,
              usedAsClassCharOffset: type.charOffset,
              usedAsClassFileUri: type.fileUri);
        } else {
          decl = typeDeclaration;
        }
        if (decl is ClassBuilder) {
          ClassBuilder interface = decl;
          if (superClass == interface) {
            addProblem(
                templateImplementsSuperClass.withArguments(interface.name),
                this.charOffset,
                noLength);
          } else if (interface.cls.name == "FutureOr" &&
              interface.cls.enclosingLibrary.importUri.scheme == "dart" &&
              interface.cls.enclosingLibrary.importUri.path == "async") {
            addProblem(messageImplementsFutureOr, this.charOffset, noLength);
          } else if (implemented.contains(interface)) {
            // Aggregate repetitions.
            problems ??= <ClassBuilder, int>{};
            problems[interface] ??= 0;
            problems[interface] = problems[interface]! + 1;
            problemsOffsets ??= <ClassBuilder, int>{};
            problemsOffsets[interface] ??= charOffset ?? TreeNode.noOffset;
          } else {
            implemented.add(interface);
          }
        }
        if (decl != superClass) {
          // TODO(eernst): Have all 'restricted supertype' checks in one place.
          if (decl is VoidTypeDeclarationBuilder) {
            fail(type, messageImplementsVoid, aliasBuilder);
          } else if (decl is NeverTypeDeclarationBuilder) {
            fail(type, messageImplementsNever, aliasBuilder);
          }
        }
      }
    }
    if (problems != null) {
      problems.forEach((ClassBuilder interface, int repetitions) {
        addProblem(
            templateImplementsRepeated.withArguments(
                interface.name, repetitions),
            problemsOffsets![interface]!,
            noLength);
      });
    }
  }

  @override
  void handleSeenCovariant(
      ClassHierarchyMembers memberHierarchy,
      Member interfaceMember,
      bool isSetter,
      callback(Member interfaceMember, bool isSetter)) {
    // When a parameter is covariant we have to check that we also
    // override the same member in all parents.
    for (Supertype supertype in interfaceMember.enclosingClass!.supers) {
      Member? member = memberHierarchy.getInterfaceMember(
          supertype.classNode, interfaceMember.name,
          setter: isSetter);
      if (member != null) {
        callback(member, isSetter);
      }
    }
  }

  @override
  bool hasUserDefinedNoSuchMethod(
      Class klass, ClassHierarchy hierarchy, Class objectClass) {
    Member? noSuchMethod = hierarchy.getDispatchTarget(klass, noSuchMethodName);
    return noSuchMethod != null && noSuchMethod.enclosingClass != objectClass;
  }

  @override
  String get fullNameForErrors {
    return isMixinApplication && !isNamedMixinApplication
        ? "${supertypeBuilder!.fullNameForErrors} with "
            "${mixedInTypeBuilder!.fullNameForErrors}"
        : name;
  }

  @override
  void checkMixinApplication(ClassHierarchy hierarchy, CoreTypes coreTypes) {
    TypeEnvironment typeEnvironment = new TypeEnvironment(coreTypes, hierarchy);
    // A mixin declaration can only be applied to a class that implements all
    // the declaration's superclass constraints.
    InterfaceType supertype = cls.supertype!.asInterfaceType;
    Substitution substitution = Substitution.fromSupertype(cls.mixedInType!);
    for (Supertype constraint in cls.mixedInClass!.superclassConstraints()) {
      InterfaceType requiredInterface =
          substitution.substituteSupertype(constraint).asInterfaceType;
      InterfaceType? implementedInterface = hierarchy.getTypeAsInstanceOf(
          supertype, requiredInterface.classNode, library.library);
      if (implementedInterface == null ||
          !typeEnvironment.areMutualSubtypes(
              implementedInterface,
              requiredInterface,
              library.isNonNullableByDefault
                  ? SubtypeCheckMode.withNullabilities
                  : SubtypeCheckMode.ignoringNullabilities)) {
        library.addProblem(
            templateMixinApplicationIncompatibleSupertype.withArguments(
                supertype,
                requiredInterface,
                cls.mixedInType!.asInterfaceType,
                library.isNonNullableByDefault),
            cls.fileOffset,
            noLength,
            cls.fileUri);
      }
    }
  }

  @override
  FunctionType? computeRedirecteeType(
      RedirectingFactoryBuilder factory, TypeEnvironment typeEnvironment) {
    ConstructorReferenceBuilder redirectionTarget = factory.redirectionTarget;
    Builder? targetBuilder = redirectionTarget.target;
    FunctionNode targetNode;
    if (targetBuilder == null) return null;
    if (targetBuilder is FunctionBuilder) {
      targetNode = targetBuilder.function;
    } else if (targetBuilder is AmbiguousBuilder) {
      // Multiple definitions with the same name: An error has already been
      // issued.
      // TODO(http://dartbug.com/35294): Unfortunate error; see also
      // https://dart-review.googlesource.com/c/sdk/+/85390/.
      return null;
    } else {
      unhandled("${redirectionTarget.target}", "computeRedirecteeType",
          charOffset, fileUri);
    }

    List<DartType>? typeArguments = factory.getTypeArguments();
    FunctionType targetFunctionType =
        targetNode.computeFunctionType(library.nonNullable);
    if (typeArguments != null &&
        targetFunctionType.typeParameters.length != typeArguments.length) {
      addProblemForRedirectingFactory(
          factory,
          templateTypeArgumentMismatch
              .withArguments(targetFunctionType.typeParameters.length),
          redirectionTarget.charOffset,
          noLength);
      return null;
    }

    // Compute the substitution of the target class type parameters if
    // [redirectionTarget] has any type arguments.
    Substitution? substitution;
    bool hasProblem = false;
    if (typeArguments != null && typeArguments.length > 0) {
      substitution = Substitution.fromPairs(
          targetFunctionType.typeParameters, typeArguments);
      for (int i = 0; i < targetFunctionType.typeParameters.length; i++) {
        TypeParameter typeParameter = targetFunctionType.typeParameters[i];
        DartType typeParameterBound =
            substitution.substituteType(typeParameter.bound);
        DartType typeArgument = typeArguments[i];
        // Check whether the [typeArgument] respects the bounds of
        // [typeParameter].
        Loader loader = library.loader;
        if (!typeEnvironment.isSubtypeOf(typeArgument, typeParameterBound,
            SubtypeCheckMode.ignoringNullabilities)) {
          addProblemForRedirectingFactory(
              factory,
              templateRedirectingFactoryIncompatibleTypeArgument.withArguments(
                  typeArgument,
                  typeParameterBound,
                  library.isNonNullableByDefault),
              redirectionTarget.charOffset,
              noLength);
          hasProblem = true;
        } else if (library.isNonNullableByDefault && loader is SourceLoader) {
          if (!typeEnvironment.isSubtypeOf(typeArgument, typeParameterBound,
              SubtypeCheckMode.withNullabilities)) {
            addProblemForRedirectingFactory(
                factory,
                templateRedirectingFactoryIncompatibleTypeArgument
                    .withArguments(typeArgument, typeParameterBound,
                        library.isNonNullableByDefault),
                redirectionTarget.charOffset,
                noLength);
            hasProblem = true;
          }
        }
      }
    } else if (typeArguments == null &&
        targetFunctionType.typeParameters.length > 0) {
      // TODO(hillerstrom): In this case, we need to perform type inference on
      // the redirectee to obtain actual type arguments which would allow the
      // following program to type check:
      //
      //    class A<T> {
      //       factory A() = B;
      //    }
      //    class B<T> implements A<T> {
      //       B();
      //    }
      //
      return null;
    }

    // Substitute if necessary.
    targetFunctionType = substitution == null
        ? targetFunctionType
        : (substitution.substituteType(targetFunctionType.withoutTypeParameters)
            as FunctionType);

    return hasProblem ? null : targetFunctionType;
  }

  @override
  String computeRedirecteeName(ConstructorReferenceBuilder redirectionTarget) {
    String targetName = redirectionTarget.fullNameForErrors;
    if (targetName == "") {
      return redirectionTarget.target!.parent!.fullNameForErrors;
    } else {
      return targetName;
    }
  }

  bool _isCyclicRedirectingFactory(RedirectingFactoryBuilder factory) {
    // We use the [tortoise and hare algorithm]
    // (https://en.wikipedia.org/wiki/Cycle_detection#Tortoise_and_hare) to
    // handle cycles.
    Builder? tortoise = factory;
    Builder? hare = factory.redirectionTarget.target;
    if (hare == factory) {
      return true;
    }
    while (tortoise != hare) {
      // Hare moves 2 steps forward.
      if (hare is! RedirectingFactoryBuilder) {
        return false;
      }
      hare = hare.redirectionTarget.target;
      if (hare == factory) {
        return true;
      }
      if (hare is! RedirectingFactoryBuilder) {
        return false;
      }
      hare = hare.redirectionTarget.target;
      if (hare == factory) {
        return true;
      }
      // Tortoise moves one step forward. No need to test type of tortoise
      // as it follows hare which already checked types.
      tortoise =
          (tortoise as RedirectingFactoryBuilder).redirectionTarget.target;
    }
    // Cycle found, but original factory doesn't belong to a cycle.
    return false;
  }

  void addProblemForRedirectingFactory(RedirectingFactoryBuilder factory,
      Message message, int charOffset, int length) {
    addProblem(message, charOffset, length);
    String text = library.loader.target.context
        .format(
            message.withLocation(fileUri, charOffset, length), Severity.error)
        .plain;
    factory.body = new RedirectingFactoryBody.error(text);
  }

  @override
  void checkRedirectingFactory(
      RedirectingFactoryBuilder factory, TypeEnvironment typeEnvironment) {
    // Check that factory declaration is not cyclic.
    if (_isCyclicRedirectingFactory(factory)) {
      addProblemForRedirectingFactory(
          factory,
          templateCyclicRedirectingFactoryConstructors
              .withArguments("${factory.member.enclosingClass!.name}"
                  "${factory.name == '' ? '' : '.${factory.name}'}"),
          factory.charOffset,
          noLength);
      return;
    }

    // The factory type cannot contain any type parameters other than those of
    // its enclosing class, because constructors cannot specify type parameters
    // of their own.
    FunctionType factoryType = factory.function
        .computeThisFunctionType(library.nonNullable)
        .withoutTypeParameters;
    FunctionType? redirecteeType =
        computeRedirecteeType(factory, typeEnvironment);

    // TODO(hillerstrom): It would be preferable to know whether a failure
    // happened during [_computeRedirecteeType].
    if (redirecteeType == null) {
      return;
    }

    // Check whether [redirecteeType] <: [factoryType].
    Loader loader = library.loader;
    if (!typeEnvironment.isSubtypeOf(
        redirecteeType, factoryType, SubtypeCheckMode.ignoringNullabilities)) {
      addProblemForRedirectingFactory(
          factory,
          templateIncompatibleRedirecteeFunctionType.withArguments(
              redirecteeType, factoryType, library.isNonNullableByDefault),
          factory.redirectionTarget.charOffset,
          noLength);
    } else if (library.isNonNullableByDefault && loader is SourceLoader) {
      if (!typeEnvironment.isSubtypeOf(
          redirecteeType, factoryType, SubtypeCheckMode.withNullabilities)) {
        addProblemForRedirectingFactory(
            factory,
            templateIncompatibleRedirecteeFunctionType.withArguments(
                redirecteeType, factoryType, library.isNonNullableByDefault),
            factory.redirectionTarget.charOffset,
            noLength);
      }
    }
  }

  @override
  void checkRedirectingFactories(TypeEnvironment typeEnvironment) {
    Map<String, MemberBuilder> constructors = this.constructors.local;
    for (Builder? constructor in constructors.values) {
      do {
        if (constructor is RedirectingFactoryBuilder) {
          checkRedirectingFactory(constructor, typeEnvironment);
        }
        constructor = constructor!.next;
      } while (constructor != null);
    }
  }

  @override
  Map<TypeParameter, DartType> getSubstitutionMap(Class superclass) {
    Supertype? supertype = cls.supertype;
    Map<TypeParameter, DartType> substitutionMap = <TypeParameter, DartType>{};
    List<DartType> arguments;
    List<TypeParameter> variables;
    Class? classNode;

    while (classNode != superclass) {
      classNode = supertype!.classNode;
      arguments = supertype.typeArguments;
      variables = classNode.typeParameters;
      supertype = classNode.supertype;
      if (variables.isNotEmpty) {
        Map<TypeParameter, DartType> directSubstitutionMap =
            <TypeParameter, DartType>{};
        for (int i = 0; i < variables.length; i++) {
          DartType argument =
              i < arguments.length ? arguments[i] : const DynamicType();
          // ignore: unnecessary_null_comparison
          if (substitutionMap != null) {
            // TODO(ahe): Investigate if requiring the caller to use
            // `substituteDeep` from `package:kernel/type_algebra.dart` instead
            // of `substitute` is faster. If so, we can simply this code.
            argument = substitute(argument, substitutionMap);
          }
          directSubstitutionMap[variables[i]] = argument;
        }
        substitutionMap = directSubstitutionMap;
      }
    }

    return substitutionMap;
  }

  @override
  Member? lookupInstanceMember(ClassHierarchy hierarchy, Name name,
      {bool isSetter: false, bool isSuper: false}) {
    Class? instanceClass = cls;
    if (isPatch) {
      assert(identical(instanceClass, origin.cls),
          "Found ${origin.cls} expected $instanceClass");
      if (isSuper) {
        // The super class is only correctly found through the origin class.
        instanceClass = origin.cls;
      } else {
        Member? member =
            hierarchy.getInterfaceMember(instanceClass, name, setter: isSetter);
        if (member?.parent == instanceClass) {
          // Only if the member is found in the patch can we use it.
          return member;
        } else {
          // Otherwise, we need to keep searching in the origin class.
          instanceClass = origin.cls;
        }
      }
    }

    if (isSuper) {
      instanceClass = instanceClass.superclass;
      if (instanceClass == null) return null;
    }
    Member? target = isSuper
        ? hierarchy.getDispatchTarget(instanceClass, name, setter: isSetter)
        : hierarchy.getInterfaceMember(instanceClass, name, setter: isSetter);
    if (isSuper && target == null) {
      if (cls.isMixinDeclaration ||
          (library.loader.target.backendTarget.enableSuperMixins &&
              this.isAbstract)) {
        target =
            hierarchy.getInterfaceMember(instanceClass, name, setter: isSetter);
      }
    }
    return target;
  }

  @override
  Constructor? lookupConstructor(Name name, {bool isSuper: false}) {
    if (name.text == "new") {
      name = new Name("", name.library);
    }

    Class? instanceClass = cls;
    if (isSuper) {
      instanceClass = instanceClass.superclass;
    }
    if (instanceClass != null) {
      for (Constructor constructor in instanceClass.constructors) {
        if (constructor.name == name) {
          return constructor;
        }
      }
    }

    /// Performs a similar lookup to [lookupConstructor], but using a slower
    /// implementation.
    Constructor? lookupConstructorWithPatches(Name name, bool isSuper) {
      ClassBuilder? builder = this.origin;

      ClassBuilder? getSuperclass(ClassBuilder builder) {
        // This way of computing the superclass is slower than using the kernel
        // objects directly.
        TypeBuilder? supertype = builder.supertypeBuilder;
        if (supertype is NamedTypeBuilder) {
          TypeDeclarationBuilder? builder = supertype.declaration;
          if (builder is ClassBuilder) return builder;
          if (builder is TypeAliasBuilder) {
            TypeDeclarationBuilder? declarationBuilder =
                builder.unaliasDeclaration(supertype.arguments,
                    isUsedAsClass: true,
                    usedAsClassCharOffset: supertype.charOffset,
                    usedAsClassFileUri: supertype.fileUri);
            if (declarationBuilder is ClassBuilder) return declarationBuilder;
          }
        }
        return null;
      }

      if (isSuper) {
        builder = getSuperclass(builder)?.origin;
      }
      if (builder != null) {
        Class cls = builder.cls;
        for (Constructor constructor in cls.constructors) {
          if (constructor.name == name) return constructor;
        }
      }
      return null;
    }

    return lookupConstructorWithPatches(name, isSuper);
  }
}

class ConstructorRedirection {
  String target;
  bool cycleReported;

  ConstructorRedirection(this.target) : cycleReported = false;
}