// 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.

// @dart = 2.9

library fasta.source_library_builder;

import 'dart:convert' show jsonEncode;

import 'package:_fe_analyzer_shared/src/scanner/token.dart' show Token;

import 'package:_fe_analyzer_shared/src/util/resolve_relative_uri.dart'
    show resolveRelativeUri;

import 'package:front_end/src/fasta/dill/dill_library_builder.dart'
    show DillLibraryBuilder;

import 'package:kernel/ast.dart' hide Combinator, MapEntry;

import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;

import 'package:kernel/clone.dart' show CloneVisitorNotMembers;

import 'package:kernel/reference_from_index.dart'
    show IndexedClass, IndexedContainer, IndexedLibrary;

import 'package:kernel/src/bounds_checks.dart'
    show
        TypeArgumentIssue,
        findTypeArgumentIssues,
        findTypeArgumentIssuesForInvocation,
        getGenericTypeName;

import 'package:kernel/type_algebra.dart' show Substitution, substitute;

import 'package:kernel/type_environment.dart'
    show SubtypeCheckMode, TypeEnvironment;

import '../../api_prototype/experimental_flags.dart';
import '../../base/nnbd_mode.dart';

import '../builder/builder.dart';
import '../builder/builtin_type_declaration_builder.dart';
import '../builder/class_builder.dart';
import '../builder/constructor_builder.dart';
import '../builder/constructor_reference_builder.dart';
import '../builder/dynamic_type_declaration_builder.dart';
import '../builder/enum_builder.dart';
import '../builder/extension_builder.dart';
import '../builder/field_builder.dart';
import '../builder/formal_parameter_builder.dart';
import '../builder/function_builder.dart';
import '../builder/function_type_builder.dart';
import '../builder/invalid_type_declaration_builder.dart';
import '../builder/library_builder.dart';
import '../builder/member_builder.dart';
import '../builder/metadata_builder.dart';
import '../builder/mixin_application_builder.dart';
import '../builder/name_iterator.dart';
import '../builder/named_type_builder.dart';
import '../builder/never_type_declaration_builder.dart';
import '../builder/nullability_builder.dart';
import '../builder/prefix_builder.dart';
import '../builder/procedure_builder.dart';
import '../builder/type_alias_builder.dart';
import '../builder/type_builder.dart';
import '../builder/type_declaration_builder.dart';
import '../builder/type_variable_builder.dart';
import '../builder/unresolved_type.dart';
import '../builder/void_type_declaration_builder.dart';

import '../combinator.dart' show Combinator;

import '../configuration.dart' show Configuration;

import '../export.dart' show Export;

import '../fasta_codes.dart';

import '../identifiers.dart' show QualifiedName, flattenName;

import '../import.dart' show Import;

import '../kernel/internal_ast.dart';

import '../kernel/kernel_builder.dart'
    show
        ImplicitFieldType,
        LoadLibraryBuilder,
        compareProcedures,
        toKernelCombinators;

import '../kernel/type_algorithms.dart'
    show
        calculateBounds,
        computeTypeVariableBuilderVariance,
        findGenericFunctionTypes,
        getInboundReferenceIssuesInType,
        getNonSimplicityIssuesForDeclaration,
        getNonSimplicityIssuesForTypeVariables,
        pendingVariance;

import '../loader.dart' show Loader;

import '../modifier.dart'
    show
        abstractMask,
        constMask,
        finalMask,
        declaresConstConstructorMask,
        hasInitializerMask,
        initializingFormalMask,
        lateMask,
        mixinDeclarationMask,
        namedMixinApplicationMask,
        staticMask;

import '../names.dart' show indexSetName;

import '../problems.dart' show unexpected, unhandled;

import '../scope.dart';

import '../type_inference/type_inferrer.dart' show TypeInferrerImpl;

import 'source_class_builder.dart' show SourceClassBuilder;

import 'source_extension_builder.dart' show SourceExtensionBuilder;

import 'source_loader.dart' show SourceLoader;

import 'source_type_alias_builder.dart';

class SourceLibraryBuilder extends LibraryBuilderImpl {
  static const String MALFORMED_URI_SCHEME = "org-dartlang-malformed-uri";

  final SourceLoader loader;

  final TypeParameterScopeBuilder libraryDeclaration;

  final List<ConstructorReferenceBuilder> constructorReferences =
      <ConstructorReferenceBuilder>[];

  final List<LibraryBuilder> parts = <LibraryBuilder>[];

  // Can I use library.parts instead? See SourceLibraryBuilder.addPart.
  final List<int> partOffsets = <int>[];

  final List<Import> imports = <Import>[];

  final List<Export> exports = <Export>[];

  final Scope importScope;

  final Uri fileUri;

  final Uri _packageUri;

  Uri get packageUriForTesting => _packageUri;

  final List<Object> accessors = <Object>[];

  String name;

  String partOfName;

  Uri partOfUri;

  List<MetadataBuilder> metadata;

  /// The current declaration that is being built. When we start parsing a
  /// declaration (class, method, and so on), we don't have enough information
  /// to create a builder and this object records its members and types until,
  /// for example, [addClass] is called.
  TypeParameterScopeBuilder currentTypeParameterScopeBuilder;

  /// Non-null if this library causes an error upon access, that is, there was
  /// an error reading its source.
  Message accessProblem;

  @override
  final Library library;

  final SourceLibraryBuilder actualOrigin;

  final List<FunctionBuilder> nativeMethods = <FunctionBuilder>[];

  final List<TypeVariableBuilder> boundlessTypeVariables =
      <TypeVariableBuilder>[];

  final List<UncheckedTypedefType> uncheckedTypedefTypes =
      <UncheckedTypedefType>[];

  // A list of alternating forwarders and the procedures they were generated
  // for.  Note that it may not include a forwarder-origin pair in cases when
  // the former does not need to be updated after the body of the latter was
  // built.
  final List<Procedure> forwardersOrigins = <Procedure>[];

  // List of types inferred in the outline.  Errors in these should be reported
  // differently than for specified types.
  // TODO(dmitryas):  Find a way to mark inferred types.
  final Set<DartType> inferredTypes = new Set<DartType>.identity();

  // While the bounds of type parameters aren't compiled yet, we can't tell the
  // default nullability of the corresponding type-parameter types.  This list
  // is used to collect such type-parameter types in order to set the
  // nullability after the bounds are built.
  final List<PendingNullability> _pendingNullabilities = <PendingNullability>[];

  // A library to use for Names generated when compiling code in this library.
  // This allows code generated in one library to use the private namespace of
  // another, for example during expression compilation (debugging).
  Library get nameOrigin => _nameOrigin ?? library;
  final Library _nameOrigin;

  final Library referencesFrom;
  final IndexedLibrary referencesFromIndexed;
  IndexedClass _currentClassReferencesFromIndexed;

  /// Exports that can't be serialized.
  ///
  /// The key is the name of the exported member.
  ///
  /// If the name is `dynamic` or `void`, this library reexports the
  /// corresponding type from `dart:core`, and the value is null.
  ///
  /// Otherwise, this represents an error (an ambiguous export). In this case,
  /// the error message is the corresponding value in the map.
  Map<String, String> unserializableExports;

  List<FieldBuilder> _implicitlyTypedFields;

  /// The language version of this library as defined by the language version
  /// of the package it belongs to, if present, or the current language version
  /// otherwise.
  ///
  /// This language version we be used as the language version for the library
  /// if the library does not contain an explicit @dart= annotation.
  final LanguageVersion packageLanguageVersion;

  /// The actual language version of this library. This is initially the
  /// [packageLanguageVersion] but will be updated if the library contains
  /// an explicit @dart= language version annotation.
  LanguageVersion _languageVersion;

  bool postponedProblemsIssued = false;
  List<PostponedProblem> postponedProblems;

  /// List of [PrefixBuilder]s for imports with prefixes.
  List<PrefixBuilder> _prefixBuilders;

  /// Set of extension declarations in scope. This is computed lazily in
  /// [forEachExtensionInScope].
  Set<ExtensionBuilder> _extensionsInScope;

  SourceLibraryBuilder.internal(
      SourceLoader loader,
      Uri fileUri,
      Uri packageUri,
      LanguageVersion packageLanguageVersion,
      Scope scope,
      SourceLibraryBuilder actualOrigin,
      Library library,
      Library nameOrigin,
      Library referencesFrom,
      bool referenceIsPartOwner)
      : this.fromScopes(
            loader,
            fileUri,
            packageUri,
            packageLanguageVersion,
            new TypeParameterScopeBuilder.library(),
            scope ?? new Scope.top(),
            actualOrigin,
            library,
            nameOrigin,
            referencesFrom);

  SourceLibraryBuilder.fromScopes(
      this.loader,
      this.fileUri,
      this._packageUri,
      this.packageLanguageVersion,
      this.libraryDeclaration,
      this.importScope,
      this.actualOrigin,
      this.library,
      this._nameOrigin,
      this.referencesFrom)
      : _languageVersion = packageLanguageVersion,
        currentTypeParameterScopeBuilder = libraryDeclaration,
        referencesFromIndexed =
            referencesFrom == null ? null : new IndexedLibrary(referencesFrom),
        super(
            fileUri, libraryDeclaration.toScope(importScope), new Scope.top()) {
    assert(
        _packageUri == null ||
            importUri.scheme != 'package' ||
            importUri.path.startsWith(_packageUri.path),
        "Foreign package uri '$_packageUri' set on library with import uri "
        "'${importUri}'.");
    assert(
        importUri.scheme != 'dart' || _packageUri == null,
        "Package uri '$_packageUri' set on dart: library with import uri "
        "'${importUri}'.");
  }

  bool _enableConstFunctionsInLibrary;
  bool _enableVarianceInLibrary;
  bool _enableNonfunctionTypeAliasesInLibrary;
  bool _enableNonNullableInLibrary;
  Version _enableNonNullableVersionInLibrary;
  bool _enableTripleShiftInLibrary;
  bool _enableExtensionMethodsInLibrary;
  bool _enableGenericMetadataInLibrary;
  bool _enableExtensionTypesInLibrary;

  bool get enableConstFunctionsInLibrary => _enableConstFunctionsInLibrary ??=
      loader.target.isExperimentEnabledInLibraryByVersion(
          ExperimentalFlag.constFunctions,
          _packageUri ?? importUri,
          languageVersion.version);

  bool get enableVarianceInLibrary => _enableVarianceInLibrary ??= loader.target
      .isExperimentEnabledInLibraryByVersion(ExperimentalFlag.variance,
          _packageUri ?? importUri, languageVersion.version);

  bool get enableNonfunctionTypeAliasesInLibrary =>
      _enableNonfunctionTypeAliasesInLibrary ??= loader.target
          .isExperimentEnabledInLibraryByVersion(
              ExperimentalFlag.nonfunctionTypeAliases,
              _packageUri ?? importUri,
              languageVersion.version);

  /// Returns `true` if the 'non-nullable' experiment is enabled for this
  /// library.
  ///
  /// Note that the library might still opt out of the experiment by having
  /// a version that is too low for opting in to the experiment.
  bool get enableNonNullableInLibrary => _enableNonNullableInLibrary ??=
      loader.target.isExperimentEnabledInLibrary(
              ExperimentalFlag.nonNullable, _packageUri ?? importUri) &&
          !isOptOutTest(library.importUri);

  Version get enableNonNullableVersionInLibrary =>
      _enableNonNullableVersionInLibrary ??= loader.target
          .getExperimentEnabledVersionInLibrary(
              ExperimentalFlag.nonNullable, _packageUri ?? importUri);

  bool get enableTripleShiftInLibrary => _enableTripleShiftInLibrary ??=
      loader.target.isExperimentEnabledInLibraryByVersion(
          ExperimentalFlag.tripleShift,
          _packageUri ?? importUri,
          languageVersion.version);

  bool get enableExtensionMethodsInLibrary =>
      _enableExtensionMethodsInLibrary ??= loader.target
          .isExperimentEnabledInLibraryByVersion(
              ExperimentalFlag.extensionMethods,
              _packageUri ?? importUri,
              languageVersion.version);

  bool get enableGenericMetadataInLibrary => _enableGenericMetadataInLibrary ??=
      loader.target.isExperimentEnabledInLibraryByVersion(
          ExperimentalFlag.genericMetadata,
          _packageUri ?? importUri,
          languageVersion.version);

  bool get enableExtensionTypesInLibrary => _enableExtensionTypesInLibrary ??=
      loader.target.isExperimentEnabledInLibraryByVersion(
          ExperimentalFlag.extensionTypes,
          _packageUri ?? importUri,
          languageVersion.version);

  void _updateLibraryNNBDSettings() {
    library.isNonNullableByDefault = isNonNullableByDefault;
    switch (loader.nnbdMode) {
      case NnbdMode.Weak:
        library.nonNullableByDefaultCompiledMode =
            NonNullableByDefaultCompiledMode.Weak;
        break;
      case NnbdMode.Strong:
        library.nonNullableByDefaultCompiledMode =
            NonNullableByDefaultCompiledMode.Strong;
        break;
      case NnbdMode.Agnostic:
        library.nonNullableByDefaultCompiledMode =
            NonNullableByDefaultCompiledMode.Agnostic;
        break;
    }
  }

  SourceLibraryBuilder(
      Uri uri,
      Uri fileUri,
      Uri packageUri,
      LanguageVersion packageLanguageVersion,
      Loader loader,
      SourceLibraryBuilder actualOrigin,
      {Scope scope,
      Library target,
      Library nameOrigin,
      Library referencesFrom,
      bool referenceIsPartOwner})
      : this.internal(
            loader,
            fileUri,
            packageUri,
            packageLanguageVersion,
            scope,
            actualOrigin,
            target ??
                (actualOrigin?.library ??
                    new Library(uri,
                        fileUri: fileUri,
                        reference: referenceIsPartOwner == true
                            ? null
                            : referencesFrom?.reference)
                  ..setLanguageVersion(packageLanguageVersion.version)),
            nameOrigin,
            referencesFrom,
            referenceIsPartOwner);

  @override
  bool get isPart => partOfName != null || partOfUri != null;

  List<UnresolvedType> get types => libraryDeclaration.types;

  @override
  bool get isSynthetic => accessProblem != null;

  TypeBuilder addType(TypeBuilder type, int charOffset) {
    currentTypeParameterScopeBuilder
        .addType(new UnresolvedType(type, charOffset, fileUri));
    return type;
  }

  bool _isNonNullableByDefault;

  @override
  bool get isNonNullableByDefault {
    assert(
        _isNonNullableByDefault == null ||
            _isNonNullableByDefault == _computeIsNonNullableByDefault(),
        "Unstable isNonNullableByDefault property, changed "
        "from ${_isNonNullableByDefault} to "
        "${_computeIsNonNullableByDefault()}");
    return _ensureIsNonNullableByDefault();
  }

  bool _ensureIsNonNullableByDefault() {
    if (_isNonNullableByDefault == null) {
      _isNonNullableByDefault = _computeIsNonNullableByDefault();
      _updateLibraryNNBDSettings();
    }
    return _isNonNullableByDefault;
  }

  bool _computeIsNonNullableByDefault() =>
      enableNonNullableInLibrary &&
      languageVersion.version >= enableNonNullableVersionInLibrary;

  static bool isOptOutTest(Uri uri) {
    String path = uri.path;
    for (String testDir in ['/tests/', '/generated_tests/']) {
      int start = path.indexOf(testDir);
      if (start == -1) continue;
      String rest = path.substring(start + testDir.length);
      return optOutTestPaths.any(rest.startsWith);
    }
    return false;
  }

  static const List<String> optOutTestPaths = [
    'co19_2/',
    'corelib_2/',
    'web_2/',
    'ffi_2',
    'language_2/',
    'lib_2/',
    'samples_2/',
    'service_2/',
    'standalone_2/',
    'vm/dart_2/', // in runtime/tests
  ];

  LanguageVersion get languageVersion {
    assert(
        _languageVersion.isFinal,
        "Attempting to read the language version of ${this} before has been "
        "finalized.");
    return _languageVersion;
  }

  void markLanguageVersionFinal() {
    _languageVersion.isFinal = true;
    _ensureIsNonNullableByDefault();
    if (!isNonNullableByDefault &&
        (loader.nnbdMode == NnbdMode.Strong ||
            loader.nnbdMode == NnbdMode.Agnostic)) {
      // In strong and agnostic mode, the language version is not allowed to
      // opt a library out of nnbd.
      if (_languageVersion.isExplicit) {
        addPostponedProblem(messageStrongModeNNBDButOptOut,
            _languageVersion.charOffset, _languageVersion.charCount, fileUri);
      } else {
        loader.registerStrongOptOutLibrary(this);
      }
      library.nonNullableByDefaultCompiledMode =
          NonNullableByDefaultCompiledMode.Invalid;
      loader.hasInvalidNnbdModeLibrary = true;
    }
  }

  /// Set the language version to an explicit major and minor version.
  ///
  /// The default language version specified by the .packages file is passed
  /// to the constructor, but the library can have source code that specifies
  /// another one which should be supported.
  ///
  /// Only the first registered language version is used.
  ///
  /// [offset] and [length] refers to the offset and length of the source code
  /// specifying the language version.
  void registerExplicitLanguageVersion(Version version,
      {int offset: 0, int length: noLength}) {
    if (_languageVersion.isExplicit) {
      // If more than once language version exists we use the first.
      return;
    }
    assert(!_languageVersion.isFinal);

    if (version > loader.target.currentSdkVersion) {
      // If trying to set a language version that is higher than the current sdk
      // version it's an error.
      addPostponedProblem(
          templateLanguageVersionTooHigh.withArguments(
              loader.target.currentSdkVersion.major,
              loader.target.currentSdkVersion.minor),
          offset,
          length,
          fileUri);
      // If the package set an OK version, but the file set an invalid version
      // we want to use the package version.
      _languageVersion = new InvalidLanguageVersion(
          fileUri, offset, length, packageLanguageVersion.version, true);
    } else {
      _languageVersion = new LanguageVersion(version, fileUri, offset, length);
    }
    library.setLanguageVersion(_languageVersion.version);
    _languageVersion.isFinal = true;
  }

  ConstructorReferenceBuilder addConstructorReference(Object name,
      List<TypeBuilder> typeArguments, String suffix, int charOffset) {
    ConstructorReferenceBuilder ref = new ConstructorReferenceBuilder(
        name, typeArguments, suffix, this, charOffset);
    constructorReferences.add(ref);
    return ref;
  }

  void beginNestedDeclaration(TypeParameterScopeKind kind, String name,
      {bool hasMembers: true}) {
    currentTypeParameterScopeBuilder =
        currentTypeParameterScopeBuilder.createNested(kind, name, hasMembers);
  }

  TypeParameterScopeBuilder endNestedDeclaration(
      TypeParameterScopeKind kind, String name) {
    assert(
        currentTypeParameterScopeBuilder.kind == kind,
        "Unexpected declaration. "
        "Trying to end a ${currentTypeParameterScopeBuilder.kind} as a $kind.");
    assert(
        (name?.startsWith(currentTypeParameterScopeBuilder.name) ??
                (name == currentTypeParameterScopeBuilder.name)) ||
            currentTypeParameterScopeBuilder.name == "operator" ||
            identical(name, "<syntax-error>"),
        "${name} != ${currentTypeParameterScopeBuilder.name}");
    TypeParameterScopeBuilder previous = currentTypeParameterScopeBuilder;
    currentTypeParameterScopeBuilder = currentTypeParameterScopeBuilder.parent;
    return previous;
  }

  bool uriIsValid(Uri uri) => uri.scheme != MALFORMED_URI_SCHEME;

  Uri resolve(Uri baseUri, String uri, int uriOffset, {isPart: false}) {
    if (uri == null) {
      addProblem(messageExpectedUri, uriOffset, noLength, fileUri);
      return new Uri(scheme: MALFORMED_URI_SCHEME);
    }
    Uri parsedUri;
    try {
      parsedUri = Uri.parse(uri);
    } on FormatException catch (e) {
      // Point to position in string indicated by the exception,
      // or to the initial quote if no position is given.
      // (Assumes the directive is using a single-line string.)
      addProblem(templateCouldNotParseUri.withArguments(uri, e.message),
          uriOffset + 1 + (e.offset ?? -1), 1, fileUri);
      return new Uri(
          scheme: MALFORMED_URI_SCHEME, query: Uri.encodeQueryComponent(uri));
    }
    if (isPart && baseUri.scheme == "dart") {
      // Resolve using special rules for dart: URIs
      return resolveRelativeUri(baseUri, parsedUri);
    } else {
      return baseUri.resolveUri(parsedUri);
    }
  }

  String computeAndValidateConstructorName(Object name, int charOffset,
      {isFactory: false}) {
    String className = currentTypeParameterScopeBuilder.name;
    String prefix;
    String suffix;
    if (name is QualifiedName) {
      prefix = name.qualifier;
      suffix = name.name;
    } else {
      prefix = name;
      suffix = null;
    }
    if (prefix == className) {
      return suffix ?? "";
    }
    if (suffix == null && !isFactory) {
      // A legal name for a regular method, but not for a constructor.
      return null;
    }

    addProblem(
        messageConstructorWithWrongName, charOffset, prefix.length, fileUri,
        context: [
          templateConstructorWithWrongNameContext
              .withArguments(currentTypeParameterScopeBuilder.name)
              .withLocation(
                  importUri,
                  currentTypeParameterScopeBuilder.charOffset,
                  currentTypeParameterScopeBuilder.name.length)
        ]);

    return suffix;
  }

  void addExport(
      List<MetadataBuilder> metadata,
      String uri,
      List<Configuration> configurations,
      List<Combinator> combinators,
      int charOffset,
      int uriOffset) {
    if (configurations != null) {
      for (Configuration config in configurations) {
        if (lookupImportCondition(config.dottedName) == config.condition) {
          uri = config.importUri;
          break;
        }
      }
    }

    LibraryBuilder exportedLibrary = loader.read(
        resolve(this.importUri, uri, uriOffset), charOffset,
        accessor: this);
    exportedLibrary.addExporter(this, combinators, charOffset);
    exports.add(new Export(this, exportedLibrary, combinators, charOffset));
  }

  String lookupImportCondition(String dottedName) {
    const String prefix = "dart.library.";
    if (!dottedName.startsWith(prefix)) return "";
    dottedName = dottedName.substring(prefix.length);
    if (!loader.target.uriTranslator.isLibrarySupported(dottedName)) return "";

    LibraryBuilder imported =
        loader.builders[new Uri(scheme: "dart", path: dottedName)];

    if (imported == null) {
      LibraryBuilder coreLibrary = loader.read(
          resolve(this.importUri,
              new Uri(scheme: "dart", path: "core").toString(), -1),
          -1,
          accessor: loader.first);
      imported = coreLibrary
          .loader.builders[new Uri(scheme: 'dart', path: dottedName)];
    }
    return imported != null && !imported.isSynthetic ? "true" : "";
  }

  void addImport(
      List<MetadataBuilder> metadata,
      String uri,
      List<Configuration> configurations,
      String prefix,
      List<Combinator> combinators,
      bool deferred,
      int charOffset,
      int prefixCharOffset,
      int uriOffset,
      int importIndex) {
    if (configurations != null) {
      for (Configuration config in configurations) {
        if (lookupImportCondition(config.dottedName) == config.condition) {
          uri = config.importUri;
          break;
        }
      }
    }

    LibraryBuilder builder = null;

    Uri resolvedUri;
    String nativePath;
    const String nativeExtensionScheme = "dart-ext:";
    if (uri.startsWith(nativeExtensionScheme)) {
      String strippedUri = uri.substring(nativeExtensionScheme.length);
      if (strippedUri.startsWith("package")) {
        resolvedUri = resolve(this.importUri, strippedUri,
            uriOffset + nativeExtensionScheme.length);
        resolvedUri = loader.target.translateUri(resolvedUri);
        nativePath = resolvedUri.toString();
      } else {
        resolvedUri = new Uri(scheme: "dart-ext", pathSegments: [uri]);
        nativePath = uri;
      }
    } else {
      resolvedUri = resolve(this.importUri, uri, uriOffset);
      builder = loader.read(resolvedUri, uriOffset, accessor: this);
    }

    imports.add(new Import(this, builder, deferred, prefix, combinators,
        configurations, charOffset, prefixCharOffset, importIndex,
        nativeImportPath: nativePath));
  }

  void addPart(List<MetadataBuilder> metadata, String uri, int charOffset) {
    Uri resolvedUri;
    Uri newFileUri;
    resolvedUri = resolve(this.importUri, uri, charOffset, isPart: true);
    newFileUri = resolve(fileUri, uri, charOffset);
    // TODO(johnniwinther): Add a LibraryPartBuilder instead of using
    // [LibraryBuilder] to represent both libraries and parts.
    parts.add(loader.read(resolvedUri, charOffset,
        fileUri: newFileUri, accessor: this));
    partOffsets.add(charOffset);

    // TODO(ahe): [metadata] should be stored, evaluated, and added to [part].
    LibraryPart part = new LibraryPart(<Expression>[], uri)
      ..fileOffset = charOffset;
    library.addPart(part);
  }

  void addPartOf(
      List<MetadataBuilder> metadata, String name, String uri, int uriOffset) {
    partOfName = name;
    if (uri != null) {
      partOfUri = resolve(this.importUri, uri, uriOffset);
      Uri newFileUri = resolve(fileUri, uri, uriOffset);
      LibraryBuilder library = loader.read(partOfUri, uriOffset,
          fileUri: newFileUri, accessor: this);
      if (loader.first == this) {
        // This is a part, and it was the first input. Let the loader know
        // about that.
        loader.first = library;
      }
    }
  }

  void addFields(List<MetadataBuilder> metadata, int modifiers, bool isTopLevel,
      TypeBuilder type, List<FieldInfo> fieldInfos) {
    for (FieldInfo info in fieldInfos) {
      bool isConst = modifiers & constMask != 0;
      bool isFinal = modifiers & finalMask != 0;
      bool potentiallyNeedInitializerInOutline = isConst || isFinal;
      Token startToken;
      if (potentiallyNeedInitializerInOutline || type == null) {
        startToken = info.initializerToken;
      }
      if (startToken != null) {
        // Extract only the tokens for the initializer expression from the
        // token stream.
        Token endToken = info.beforeLast;
        endToken.setNext(new Token.eof(endToken.next.offset));
        new Token.eof(startToken.previous.offset).setNext(startToken);
      }
      bool hasInitializer = info.initializerToken != null;
      addField(metadata, modifiers, isTopLevel, type, info.name,
          info.charOffset, info.charEndOffset, startToken, hasInitializer,
          constInitializerToken:
              potentiallyNeedInitializerInOutline ? startToken : null);
    }
  }

  @override
  Builder addBuilder(String name, Builder declaration, int charOffset,
      {Reference getterReference, Reference setterReference}) {
    // TODO(ahe): Set the parent correctly here. Could then change the
    // implementation of MemberBuilder.isTopLevel to test explicitly for a
    // LibraryBuilder.
    if (name == null) {
      unhandled("null", "name", charOffset, fileUri);
    }
    if (getterReference != null) {
      loader.buildersCreatedWithReferences[getterReference] = declaration;
    }
    if (setterReference != null) {
      loader.buildersCreatedWithReferences[setterReference] = declaration;
    }
    if (currentTypeParameterScopeBuilder == libraryDeclaration) {
      if (declaration is MemberBuilder) {
        declaration.parent = this;
      } else if (declaration is TypeDeclarationBuilder) {
        declaration.parent = this;
      } else if (declaration is PrefixBuilder) {
        assert(declaration.parent == this);
      } else {
        return unhandled(
            "${declaration.runtimeType}", "addBuilder", charOffset, fileUri);
      }
    } else {
      assert(currentTypeParameterScopeBuilder.parent == libraryDeclaration);
    }
    bool isConstructor = declaration is FunctionBuilder &&
        (declaration.isConstructor || declaration.isFactory);
    if (!isConstructor && name == currentTypeParameterScopeBuilder.name) {
      addProblem(
          messageMemberWithSameNameAsClass, charOffset, noLength, fileUri);
    }
    Map<String, Builder> members = isConstructor
        ? currentTypeParameterScopeBuilder.constructors
        : (declaration.isSetter
            ? currentTypeParameterScopeBuilder.setters
            : currentTypeParameterScopeBuilder.members);
    Builder existing = members[name];

    if (existing == declaration) return existing;

    if (declaration.next != null && declaration.next != existing) {
      unexpected(
          "${declaration.next.fileUri}@${declaration.next.charOffset}",
          "${existing?.fileUri}@${existing?.charOffset}",
          declaration.charOffset,
          declaration.fileUri);
    }
    declaration.next = existing;
    if (declaration is PrefixBuilder && existing is PrefixBuilder) {
      assert(existing.next is! PrefixBuilder);
      Builder deferred;
      Builder other;
      if (declaration.deferred) {
        deferred = declaration;
        other = existing;
      } else if (existing.deferred) {
        deferred = existing;
        other = declaration;
      }
      if (deferred != null) {
        addProblem(templateDeferredPrefixDuplicated.withArguments(name),
            deferred.charOffset, noLength, fileUri,
            context: [
              templateDeferredPrefixDuplicatedCause
                  .withArguments(name)
                  .withLocation(fileUri, other.charOffset, noLength)
            ]);
      }
      return existing
        ..exportScope.merge(declaration.exportScope,
            (String name, Builder existing, Builder member) {
          return computeAmbiguousDeclaration(
              name, existing, member, charOffset);
        });
    } else if (isDuplicatedDeclaration(existing, declaration)) {
      String fullName = name;
      if (isConstructor) {
        if (name.isEmpty) {
          fullName = currentTypeParameterScopeBuilder.name;
        } else {
          fullName = "${currentTypeParameterScopeBuilder.name}.$name";
        }
      }
      addProblem(templateDuplicatedDeclaration.withArguments(fullName),
          charOffset, fullName.length, declaration.fileUri,
          context: <LocatedMessage>[
            templateDuplicatedDeclarationCause
                .withArguments(fullName)
                .withLocation(
                    existing.fileUri, existing.charOffset, fullName.length)
          ]);
    } else if (declaration.isExtension) {
      // We add the extension declaration to the extension scope only if its
      // name is unique. Only the first of duplicate extensions is accessible
      // by name or by resolution and the remaining are dropped for the output.
      currentTypeParameterScopeBuilder.extensions.add(declaration);
    }
    if (declaration is PrefixBuilder) {
      _prefixBuilders ??= <PrefixBuilder>[];
      _prefixBuilders.add(declaration);
    }
    return members[name] = declaration;
  }

  bool isDuplicatedDeclaration(Builder existing, Builder other) {
    if (existing == null) return false;
    Builder next = existing.next;
    if (next == null) {
      if (existing.isGetter && other.isSetter) return false;
      if (existing.isSetter && other.isGetter) return false;
    } else {
      if (next is ClassBuilder && !next.isMixinApplication) return true;
    }
    if (existing is ClassBuilder && other is ClassBuilder) {
      // We allow multiple mixin applications with the same name. An
      // alternative is to share these mixin applications. This situation can
      // happen if you have `class A extends Object with Mixin {}` and `class B
      // extends Object with Mixin {}` in the same library.
      return !existing.isMixinApplication || !other.isMixinApplication;
    }
    return true;
  }

  /// Checks [scope] for conflicts between setters and non-setters and reports
  /// them in [sourceLibraryBuilder].
  ///
  /// If [checkForInstanceVsStaticConflict] is `true`, conflicts between
  /// instance and static members of the same name are reported.
  ///
  /// If [checkForMethodVsSetterConflict] is `true`, conflicts between
  /// methods and setters of the same name are reported.
  static void checkMemberConflicts(
      SourceLibraryBuilder sourceLibraryBuilder, Scope scope,
      {bool checkForInstanceVsStaticConflict,
      bool checkForMethodVsSetterConflict}) {
    assert(checkForInstanceVsStaticConflict != null);
    assert(checkForMethodVsSetterConflict != null);

    scope.forEachLocalSetter((String name, MemberBuilder setter) {
      Builder getable = scope.lookupLocalMember(name, setter: false);
      if (getable == null) {
        // Setter without getter.
        return;
      }

      bool isConflictingSetter = false;
      Set<Builder> conflictingGetables = {};
      for (Builder currentGetable = getable;
          currentGetable != null;
          currentGetable = currentGetable.next) {
        if (currentGetable is FieldBuilder) {
          if (currentGetable.isAssignable) {
            // Setter with writable field.
            isConflictingSetter = true;
            conflictingGetables.add(currentGetable);
          }
        } else if (checkForMethodVsSetterConflict && !currentGetable.isGetter) {
          // Setter with method.
          conflictingGetables.add(currentGetable);
        }
      }
      for (MemberBuilderImpl currentSetter = setter;
          currentSetter != null;
          currentSetter = currentSetter.next) {
        bool conflict = conflictingGetables.isNotEmpty;
        for (Builder currentGetable = getable;
            currentGetable != null;
            currentGetable = currentGetable.next) {
          if (checkForInstanceVsStaticConflict &&
              currentGetable.isDeclarationInstanceMember !=
                  currentSetter.isDeclarationInstanceMember) {
            conflict = true;
            conflictingGetables.add(currentGetable);
          }
        }
        if (isConflictingSetter) {
          currentSetter.isConflictingSetter = true;
        }
        if (conflict) {
          if (currentSetter.isConflictingSetter) {
            sourceLibraryBuilder.addProblem(
                templateConflictsWithImplicitSetter.withArguments(name),
                currentSetter.charOffset,
                noLength,
                currentSetter.fileUri);
          } else {
            sourceLibraryBuilder.addProblem(
                templateConflictsWithMember.withArguments(name),
                currentSetter.charOffset,
                noLength,
                currentSetter.fileUri);
          }
        }
      }
      for (Builder conflictingGetable in conflictingGetables) {
        // TODO(ahe): Context argument to previous message?
        sourceLibraryBuilder.addProblem(
            templateConflictsWithSetter.withArguments(name),
            conflictingGetable.charOffset,
            noLength,
            conflictingGetable.fileUri);
      }
    });
  }

  /// Builds the core AST structure of this library as needed for the outline.
  Library build(LibraryBuilder coreLibrary, {bool modifyTarget}) {
    checkMemberConflicts(this, scope,
        checkForInstanceVsStaticConflict: false,
        checkForMethodVsSetterConflict: true);

    Iterator<Builder> iterator = this.iterator;
    while (iterator.moveNext()) {
      buildBuilder(iterator.current, coreLibrary);
    }

    if (modifyTarget == false) return library;

    library.isSynthetic = isSynthetic;
    addDependencies(library, new Set<SourceLibraryBuilder>());

    library.name = name;
    library.procedures.sort(compareProcedures);

    if (unserializableExports != null) {
      Name fieldName = new Name("_exports#", library);
      Reference getterReference =
          referencesFromIndexed?.lookupGetterReference(fieldName);
      library.addField(new Field.immutable(fieldName,
          initializer: new StringLiteral(jsonEncode(unserializableExports)),
          isStatic: true,
          isConst: true,
          getterReference: getterReference));
    }

    return library;
  }

  void validatePart(SourceLibraryBuilder library, Set<Uri> usedParts) {
    if (library != null && parts.isNotEmpty) {
      // If [library] is null, we have already reported a problem that this
      // part is orphaned.
      List<LocatedMessage> context = <LocatedMessage>[
        messagePartInPartLibraryContext.withLocation(library.fileUri, -1, 1),
      ];
      for (int offset in partOffsets) {
        addProblem(messagePartInPart, offset, noLength, fileUri,
            context: context);
      }
      for (SourceLibraryBuilder part in parts) {
        // Mark this part as used so we don't report it as orphaned.
        usedParts.add(part.importUri);
      }
    }
    parts.clear();
    if (exporters.isNotEmpty) {
      List<LocatedMessage> context = <LocatedMessage>[
        messagePartExportContext.withLocation(fileUri, -1, 1),
      ];
      for (Export export in exporters) {
        export.exporter.addProblem(
            messagePartExport, export.charOffset, "export".length, null,
            context: context);
      }
    }
  }

  void includeParts(Set<Uri> usedParts) {
    Set<Uri> seenParts = new Set<Uri>();
    for (int i = 0; i < parts.length; i++) {
      LibraryBuilder part = parts[i];
      int partOffset = partOffsets[i];
      if (part == this) {
        addProblem(messagePartOfSelf, -1, noLength, fileUri);
      } else if (seenParts.add(part.fileUri)) {
        if (part.partOfLibrary != null) {
          addProblem(messagePartOfTwoLibraries, -1, noLength, part.fileUri,
              context: [
                messagePartOfTwoLibrariesContext.withLocation(
                    part.partOfLibrary.fileUri, -1, noLength),
                messagePartOfTwoLibrariesContext.withLocation(
                    this.fileUri, -1, noLength)
              ]);
        } else {
          if (isPatch) {
            usedParts.add(part.fileUri);
          } else {
            usedParts.add(part.importUri);
          }
          includePart(part, usedParts, partOffset);
        }
      } else {
        addProblem(templatePartTwice.withArguments(part.fileUri), -1, noLength,
            fileUri);
      }
    }
  }

  bool includePart(LibraryBuilder part, Set<Uri> usedParts, int partOffset) {
    if (part is SourceLibraryBuilder) {
      if (part.partOfUri != null) {
        if (uriIsValid(part.partOfUri) && part.partOfUri != importUri) {
          // This is an error, but the part is not removed from the list of
          // parts, so that metadata annotations can be associated with it.
          addProblem(
              templatePartOfUriMismatch.withArguments(
                  part.fileUri, importUri, part.partOfUri),
              partOffset,
              noLength,
              fileUri);
          return false;
        }
      } else if (part.partOfName != null) {
        if (name != null) {
          if (part.partOfName != name) {
            // This is an error, but the part is not removed from the list of
            // parts, so that metadata annotations can be associated with it.
            addProblem(
                templatePartOfLibraryNameMismatch.withArguments(
                    part.fileUri, name, part.partOfName),
                partOffset,
                noLength,
                fileUri);
            return false;
          }
        } else {
          // This is an error, but the part is not removed from the list of
          // parts, so that metadata annotations can be associated with it.
          addProblem(
              templatePartOfUseUri.withArguments(
                  part.fileUri, fileUri, part.partOfName),
              partOffset,
              noLength,
              fileUri);
          return false;
        }
      } else {
        // This is an error, but the part is not removed from the list of parts,
        // so that metadata annotations can be associated with it.
        assert(!part.isPart);
        if (uriIsValid(part.fileUri)) {
          addProblem(templateMissingPartOf.withArguments(part.fileUri),
              partOffset, noLength, fileUri);
        }
        return false;
      }

      // Language versions have to match. Except if (at least) one of them is
      // invalid in which case we've already gotten an error about this.
      if (languageVersion != part.languageVersion &&
          languageVersion.valid &&
          part.languageVersion.valid) {
        // This is an error, but the part is not removed from the list of
        // parts, so that metadata annotations can be associated with it.
        List<LocatedMessage> context = <LocatedMessage>[];
        if (languageVersion.isExplicit) {
          context.add(messageLanguageVersionLibraryContext.withLocation(
              languageVersion.fileUri,
              languageVersion.charOffset,
              languageVersion.charCount));
        }
        if (part.languageVersion.isExplicit) {
          context.add(messageLanguageVersionPartContext.withLocation(
              part.languageVersion.fileUri,
              part.languageVersion.charOffset,
              part.languageVersion.charCount));
        }
        addProblem(
            messageLanguageVersionMismatchInPart, partOffset, noLength, fileUri,
            context: context);
      }

      part.validatePart(this, usedParts);
      NameIterator partDeclarations = part.nameIterator;
      while (partDeclarations.moveNext()) {
        String name = partDeclarations.name;
        Builder declaration = partDeclarations.current;

        if (declaration.next != null) {
          List<Builder> duplicated = <Builder>[];
          while (declaration.next != null) {
            duplicated.add(declaration);
            partDeclarations.moveNext();
            declaration = partDeclarations.current;
          }
          duplicated.add(declaration);
          // Handle duplicated declarations in the part.
          //
          // Duplicated declarations are handled by creating a linked list using
          // the `next` field. This is preferred over making all scope entries
          // be a `List<Declaration>`.
          //
          // We maintain the linked list so that the last entry is easy to
          // recognize (it's `next` field is null). This means that it is
          // reversed with respect to source code order. Since kernel doesn't
          // allow duplicated declarations, we ensure that we only add the first
          // declaration to the kernel tree.
          //
          // Since the duplicated declarations are stored in reverse order, we
          // iterate over them in reverse order as this is simpler and normally
          // not a problem. However, in this case we need to call [addBuilder]
          // in source order as it would otherwise create cycles.
          //
          // We also need to be careful preserving the order of the links. The
          // part library still keeps these declarations in its scope so that
          // DietListener can find them.
          for (int i = duplicated.length; i > 0; i--) {
            Builder declaration = duplicated[i - 1];
            // No reference: There should be no duplicates when using
            // references.
            addBuilder(name, declaration, declaration.charOffset);
          }
        } else {
          // No reference: The part is in the same loader so the reference
          // - if needed - was already added.
          addBuilder(name, declaration, declaration.charOffset);
        }
      }
      types.addAll(part.types);
      constructorReferences.addAll(part.constructorReferences);
      part.partOfLibrary = this;
      part.scope.becomePartOf(scope);
      // TODO(ahe): Include metadata from part?

      nativeMethods.addAll(part.nativeMethods);
      boundlessTypeVariables.addAll(part.boundlessTypeVariables);
      // Check that the targets are different. This is not normally a problem
      // but is for patch files.
      if (library != part.library && part.library.problemsAsJson != null) {
        library.problemsAsJson ??= <String>[];
        library.problemsAsJson.addAll(part.library.problemsAsJson);
      }
      List<FieldBuilder> partImplicitlyTypedFields =
          part.takeImplicitlyTypedFields();
      if (partImplicitlyTypedFields != null) {
        if (_implicitlyTypedFields == null) {
          _implicitlyTypedFields = partImplicitlyTypedFields;
        } else {
          _implicitlyTypedFields.addAll(partImplicitlyTypedFields);
        }
      }
      return true;
    } else {
      assert(part is DillLibraryBuilder);
      // Trying to add a dill library builder as a part means that it exists
      // as a stand-alone library in the dill file.
      // This means, that it's not a part (if it had been it would be been
      // "merged in" to the real library and thus not been a library on its own)
      // so we behave like if it's a library with a missing "part of"
      // declaration (i.e. as it was a SourceLibraryBuilder without a "part of"
      // declaration).
      if (uriIsValid(part.fileUri)) {
        addProblem(templateMissingPartOf.withArguments(part.fileUri),
            partOffset, noLength, fileUri);
      }
      return false;
    }
  }

  void buildInitialScopes() {
    NameIterator iterator = nameIterator;
    while (iterator.moveNext()) {
      addToExportScope(iterator.name, iterator.current);
    }
  }

  void addImportsToScope() {
    bool explicitCoreImport = this == loader.coreLibrary;
    for (Import import in imports) {
      if (import.imported == loader.coreLibrary) {
        explicitCoreImport = true;
      }
      if (import.imported?.isPart ?? false) {
        addProblem(
            templatePartOfInLibrary.withArguments(import.imported.fileUri),
            import.charOffset,
            noLength,
            fileUri);
      }
      import.finalizeImports(this);
    }
    if (!explicitCoreImport) {
      loader.coreLibrary.exportScope.forEach((String name, Builder member) {
        addToScope(name, member, -1, true);
      });
    }

    exportScope.forEach((String name, Builder member) {
      if (member.parent != this) {
        switch (name) {
          case "dynamic":
          case "void":
          case "Never":
            unserializableExports ??= <String, String>{};
            unserializableExports[name] = null;
            break;

          default:
            if (member is InvalidTypeDeclarationBuilder) {
              unserializableExports ??= <String, String>{};
              unserializableExports[name] = member.message.message;
            } else {
              // Eventually (in #buildBuilder) members aren't added to the
              // library if the have 'next' pointers, so don't add them as
              // additionalExports either. Add the last one only (the one that
              // will eventually be added to the library).
              Builder memberLast = member;
              while (memberLast.next != null) {
                memberLast = memberLast.next;
              }
              if (memberLast is ClassBuilder) {
                library.additionalExports.add(memberLast.cls.reference);
              } else if (memberLast is TypeAliasBuilder) {
                library.additionalExports.add(memberLast.typedef.reference);
              } else if (memberLast is ExtensionBuilder) {
                library.additionalExports.add(memberLast.extension.reference);
              } else if (memberLast is MemberBuilder) {
                for (Member member in memberLast.exportedMembers) {
                  if (member is Field) {
                    // For fields add both getter and setter references
                    // so replacing a field with a getter/setter pair still
                    // exports correctly.
                    library.additionalExports.add(member.getterReference);
                    if (member.hasSetter) {
                      library.additionalExports.add(member.setterReference);
                    }
                  } else {
                    library.additionalExports.add(member.reference);
                  }
                }
              } else {
                unhandled('member', 'exportScope', memberLast.charOffset,
                    memberLast.fileUri);
              }
            }
        }
      }
    });
  }

  @override
  void addToScope(String name, Builder member, int charOffset, bool isImport) {
    Builder existing =
        importScope.lookupLocalMember(name, setter: member.isSetter);
    if (existing != null) {
      if (existing != member) {
        importScope.addLocalMember(
            name,
            computeAmbiguousDeclaration(name, existing, member, charOffset,
                isImport: isImport),
            setter: member.isSetter);
      }
    } else {
      importScope.addLocalMember(name, member, setter: member.isSetter);
    }
    if (member.isExtension) {
      importScope.addExtension(member);
    }
  }

  /// Resolves all unresolved types in [types]. The list of types is cleared
  /// when done.
  int resolveTypes() {
    int typeCount = types.length;
    for (UnresolvedType t in types) {
      t.resolveIn(scope, this);
      t.checkType(this);
    }
    types.clear();
    return typeCount;
  }

  @override
  int resolveConstructors(_) {
    int count = 0;
    Iterator<Builder> iterator = this.iterator;
    while (iterator.moveNext()) {
      count += iterator.current.resolveConstructors(this);
    }
    return count;
  }

  @override
  String get fullNameForErrors {
    // TODO(ahe): Consider if we should use relativizeUri here. The downside to
    // doing that is that this URI may be used in an error message. Ideally, we
    // should create a class that represents qualified names that we can
    // relativize when printing a message, but still store the full URI in
    // .dill files.
    return name ?? "<library '$fileUri'>";
  }

  @override
  void recordAccess(int charOffset, int length, Uri fileUri) {
    accessors.add(fileUri);
    accessors.add(charOffset);
    accessors.add(length);
    if (accessProblem != null) {
      addProblem(accessProblem, charOffset, length, fileUri);
    }
  }

  void addProblemAtAccessors(Message message) {
    if (accessProblem == null) {
      if (accessors.isEmpty && this == loader.first) {
        // This is the entry point library, and nobody access it directly. So
        // we need to report a problem.
        loader.addProblem(message, -1, 1, null);
      }
      for (int i = 0; i < accessors.length; i += 3) {
        Uri accessor = accessors[i];
        int charOffset = accessors[i + 1];
        int length = accessors[i + 2];
        addProblem(message, charOffset, length, accessor);
      }
      accessProblem = message;
    }
  }

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

  Uri get importUri => library.importUri;

  void addSyntheticDeclarationOfDynamic() {
    addBuilder("dynamic",
        new DynamicTypeDeclarationBuilder(const DynamicType(), this, -1), -1);
  }

  void addSyntheticDeclarationOfNever() {
    addBuilder(
        "Never",
        new NeverTypeDeclarationBuilder(
            const NeverType.nonNullable(), this, -1),
        -1);
  }

  void addSyntheticDeclarationOfNull() {
    // TODO(dmitryas): Uncomment the following when the Null class is removed
    // from the SDK.
    //addBuilder("Null", new NullTypeBuilder(const NullType(), this, -1), -1);
  }

  TypeBuilder addNamedType(Object name, NullabilityBuilder nullabilityBuilder,
      List<TypeBuilder> arguments, int charOffset) {
    return addType(
        new NamedTypeBuilder(
            name, nullabilityBuilder, arguments, fileUri, charOffset),
        charOffset);
  }

  TypeBuilder addMixinApplication(
      TypeBuilder supertype, List<TypeBuilder> mixins, int charOffset) {
    return addType(
        new MixinApplicationBuilder(supertype, mixins, fileUri, charOffset),
        charOffset);
  }

  TypeBuilder addVoidType(int charOffset) {
    // 'void' is always nullable.
    return addNamedType(
        "void", const NullabilityBuilder.nullable(), null, charOffset)
      ..bind(
          new VoidTypeDeclarationBuilder(const VoidType(), this, charOffset));
  }

  /// Add a problem that might not be reported immediately.
  ///
  /// Problems will be issued after source information has been added.
  /// Once the problems has been issued, adding a new "postponed" problem will
  /// be issued immediately.
  void addPostponedProblem(
      Message message, int charOffset, int length, Uri fileUri) {
    if (postponedProblemsIssued) {
      addProblem(message, charOffset, length, fileUri);
    } else {
      postponedProblems ??= <PostponedProblem>[];
      postponedProblems
          .add(new PostponedProblem(message, charOffset, length, fileUri));
    }
  }

  void issuePostponedProblems() {
    postponedProblemsIssued = true;
    if (postponedProblems == null) return;
    for (int i = 0; i < postponedProblems.length; ++i) {
      PostponedProblem postponedProblem = postponedProblems[i];
      addProblem(postponedProblem.message, postponedProblem.charOffset,
          postponedProblem.length, postponedProblem.fileUri);
    }
    postponedProblems = null;
  }

  @override
  FormattedMessage addProblem(
      Message message, int charOffset, int length, Uri fileUri,
      {bool wasHandled: false,
      List<LocatedMessage> context,
      Severity severity,
      bool problemOnLibrary: false}) {
    FormattedMessage formattedMessage = super.addProblem(
        message, charOffset, length, fileUri,
        wasHandled: wasHandled,
        context: context,
        severity: severity,
        problemOnLibrary: true);
    if (formattedMessage != null) {
      library.problemsAsJson ??= <String>[];
      library.problemsAsJson.add(formattedMessage.toJsonString());
    }
    return formattedMessage;
  }

  void addClass(
      List<MetadataBuilder> metadata,
      int modifiers,
      String className,
      List<TypeVariableBuilder> typeVariables,
      TypeBuilder supertype,
      List<TypeBuilder> interfaces,
      int startOffset,
      int nameOffset,
      int endOffset,
      int supertypeOffset) {
    _addClass(
        TypeParameterScopeKind.classDeclaration,
        metadata,
        modifiers,
        className,
        typeVariables,
        supertype,
        interfaces,
        startOffset,
        nameOffset,
        endOffset,
        supertypeOffset);
  }

  void addMixinDeclaration(
      List<MetadataBuilder> metadata,
      int modifiers,
      String className,
      List<TypeVariableBuilder> typeVariables,
      TypeBuilder supertype,
      List<TypeBuilder> interfaces,
      int startOffset,
      int nameOffset,
      int endOffset,
      int supertypeOffset) {
    _addClass(
        TypeParameterScopeKind.mixinDeclaration,
        metadata,
        modifiers,
        className,
        typeVariables,
        supertype,
        interfaces,
        startOffset,
        nameOffset,
        endOffset,
        supertypeOffset);
  }

  void _addClass(
      TypeParameterScopeKind kind,
      List<MetadataBuilder> metadata,
      int modifiers,
      String className,
      List<TypeVariableBuilder> typeVariables,
      TypeBuilder supertype,
      List<TypeBuilder> interfaces,
      int startOffset,
      int nameOffset,
      int endOffset,
      int supertypeOffset) {
    // Nested declaration began in `OutlineBuilder.beginClassDeclaration`.
    TypeParameterScopeBuilder declaration =
        endNestedDeclaration(kind, className)
          ..resolveTypes(typeVariables, this);
    assert(declaration.parent == libraryDeclaration);
    Map<String, MemberBuilder> members = declaration.members;
    Map<String, MemberBuilder> constructors = declaration.constructors;
    Map<String, MemberBuilder> setters = declaration.setters;

    Scope classScope = new Scope(
        local: members,
        setters: setters,
        parent: scope.withTypeVariables(typeVariables),
        debugName: "class $className",
        isModifiable: false);

    // When looking up a constructor, we don't consider type variables or the
    // library scope.
    ConstructorScope constructorScope =
        new ConstructorScope(className, constructors);
    bool isMixinDeclaration = false;
    if (modifiers & mixinDeclarationMask != 0) {
      isMixinDeclaration = true;
      modifiers = (modifiers & ~mixinDeclarationMask) | abstractMask;
    }
    if (declaration.declaresConstConstructor) {
      modifiers |= declaresConstConstructorMask;
    }
    Class referencesFromClass;
    if (referencesFrom != null) {
      referencesFromClass = referencesFromIndexed.lookupClass(className);
      assert(referencesFromClass == null ||
          _currentClassReferencesFromIndexed != null);
    }
    ClassBuilder classBuilder = new SourceClassBuilder(
        metadata,
        modifiers,
        className,
        typeVariables,
        applyMixins(supertype, startOffset, nameOffset, endOffset, className,
            isMixinDeclaration,
            typeVariables: typeVariables),
        interfaces,
        // TODO(johnniwinther): Add the `on` clause types of a mixin declaration
        // here.
        null,
        classScope,
        constructorScope,
        this,
        new List<ConstructorReferenceBuilder>.from(constructorReferences),
        startOffset,
        nameOffset,
        endOffset,
        referencesFromClass,
        _currentClassReferencesFromIndexed,
        isMixinDeclaration: isMixinDeclaration);

    constructorReferences.clear();
    Map<String, TypeVariableBuilder> typeVariablesByName =
        checkTypeVariables(typeVariables, classBuilder);
    void setParent(String name, MemberBuilder member) {
      while (member != null) {
        member.parent = classBuilder;
        member = member.next;
      }
    }

    void setParentAndCheckConflicts(String name, MemberBuilder member) {
      if (typeVariablesByName != null) {
        TypeVariableBuilder tv = typeVariablesByName[name];
        if (tv != null) {
          classBuilder.addProblem(
              templateConflictsWithTypeVariable.withArguments(name),
              member.charOffset,
              name.length,
              context: [
                messageConflictsWithTypeVariableCause.withLocation(
                    tv.fileUri, tv.charOffset, name.length)
              ]);
        }
      }
      setParent(name, member);
    }

    members.forEach(setParentAndCheckConflicts);
    constructors.forEach(setParentAndCheckConflicts);
    setters.forEach(setParentAndCheckConflicts);
    addBuilder(className, classBuilder, nameOffset,
        getterReference: referencesFromClass?.reference);
  }

  Map<String, TypeVariableBuilder> checkTypeVariables(
      List<TypeVariableBuilder> typeVariables, Builder owner) {
    if (typeVariables?.isEmpty ?? true) return null;
    Map<String, TypeVariableBuilder> typeVariablesByName =
        <String, TypeVariableBuilder>{};
    for (TypeVariableBuilder tv in typeVariables) {
      TypeVariableBuilder existing = typeVariablesByName[tv.name];
      if (existing != null) {
        if (existing.isExtensionTypeParameter) {
          // The type parameter from the extension is shadowed by the type
          // parameter from the member. Rename the shadowed type parameter.
          existing.parameter.name = '#${existing.name}';
          typeVariablesByName[tv.name] = tv;
        } else {
          addProblem(messageTypeVariableDuplicatedName, tv.charOffset,
              tv.name.length, fileUri,
              context: [
                templateTypeVariableDuplicatedNameCause
                    .withArguments(tv.name)
                    .withLocation(
                        fileUri, existing.charOffset, existing.name.length)
              ]);
        }
      } else {
        typeVariablesByName[tv.name] = tv;
        if (owner is ClassBuilder) {
          // Only classes and type variables can't have the same name. See
          // [#29555](https://github.com/dart-lang/sdk/issues/29555).
          if (tv.name == owner.name) {
            addProblem(messageTypeVariableSameNameAsEnclosing, tv.charOffset,
                tv.name.length, fileUri);
          }
        }
      }
    }
    return typeVariablesByName;
  }

  void checkGetterSetterTypes(ProcedureBuilder getterBuilder,
      ProcedureBuilder setterBuilder, TypeEnvironment typeEnvironment) {
    DartType getterType;
    List<TypeParameter> getterExtensionTypeParameters;
    if (getterBuilder.isExtensionInstanceMember) {
      // An extension instance getter
      //
      //     extension E<T> on A {
      //       T get property => ...
      //     }
      //
      // is encoded as a top level method
      //
      //   T# E#get#property<T#>(A #this) => ...
      //
      Procedure procedure = getterBuilder.procedure;
      getterType = procedure.function.returnType;
      getterExtensionTypeParameters = procedure.function.typeParameters;
    } else {
      getterType = getterBuilder.procedure.getterType;
    }
    DartType setterType;
    if (setterBuilder.isExtensionInstanceMember) {
      // An extension instance setter
      //
      //     extension E<T> on A {
      //       void set property(T value) { ... }
      //     }
      //
      // is encoded as a top level method
      //
      //   void E#set#property<T#>(A #this, T# value) { ... }
      //
      Procedure procedure = setterBuilder.procedure;
      setterType = procedure.function.positionalParameters[1].type;
      if (getterExtensionTypeParameters != null &&
          getterExtensionTypeParameters.isNotEmpty) {
        // We substitute the setter type parameters for the getter type
        // parameters to check them below in a shared context.
        List<TypeParameter> setterExtensionTypeParameters =
            procedure.function.typeParameters;
        assert(getterExtensionTypeParameters.length ==
            setterExtensionTypeParameters.length);
        setterType = Substitution.fromPairs(
                setterExtensionTypeParameters,
                new List<DartType>.generate(
                    getterExtensionTypeParameters.length,
                    (int index) => new TypeParameterType.forAlphaRenaming(
                        setterExtensionTypeParameters[index],
                        getterExtensionTypeParameters[index])))
            .substituteType(setterType);
      }
    } else {
      setterType = setterBuilder.procedure.setterType;
    }

    if (getterType is InvalidType || setterType is InvalidType) {
      // Don't report a problem as something else is wrong that has already
      // been reported.
    } else {
      bool isValid = typeEnvironment.isSubtypeOf(
          getterType,
          setterType,
          library.isNonNullableByDefault
              ? SubtypeCheckMode.withNullabilities
              : SubtypeCheckMode.ignoringNullabilities);
      if (!isValid && !library.isNonNullableByDefault) {
        // Allow assignability in legacy libraries.
        isValid = typeEnvironment.isSubtypeOf(
            setterType, getterType, SubtypeCheckMode.ignoringNullabilities);
      }
      if (!isValid) {
        String getterMemberName = getterBuilder.fullNameForErrors;
        String setterMemberName = setterBuilder.fullNameForErrors;
        Template<Message Function(DartType, String, DartType, String, bool)>
            template = library.isNonNullableByDefault
                ? templateInvalidGetterSetterType
                : templateInvalidGetterSetterTypeLegacy;
        addProblem(
            template.withArguments(getterType, getterMemberName, setterType,
                setterMemberName, library.isNonNullableByDefault),
            getterBuilder.charOffset,
            getterBuilder.name.length,
            getterBuilder.fileUri,
            context: [
              templateInvalidGetterSetterTypeSetterContext
                  .withArguments(setterMemberName)
                  .withLocation(setterBuilder.fileUri, setterBuilder.charOffset,
                      setterBuilder.name.length)
            ]);
      }
    }
  }

  void addExtensionDeclaration(
      List<MetadataBuilder> metadata,
      int modifiers,
      String extensionName,
      List<TypeVariableBuilder> typeVariables,
      TypeBuilder type,
      int startOffset,
      int nameOffset,
      int endOffset) {
    // Nested declaration began in `OutlineBuilder.beginExtensionDeclaration`.
    TypeParameterScopeBuilder declaration = endNestedDeclaration(
        TypeParameterScopeKind.extensionDeclaration, extensionName)
      ..resolveTypes(typeVariables, this);
    assert(declaration.parent == libraryDeclaration);
    Map<String, MemberBuilder> members = declaration.members;
    Map<String, MemberBuilder> constructors = declaration.constructors;
    Map<String, MemberBuilder> setters = declaration.setters;

    Scope classScope = new Scope(
        local: members,
        setters: setters,
        parent: scope.withTypeVariables(typeVariables),
        debugName: "extension $extensionName",
        isModifiable: false);

    Extension referenceFrom =
        referencesFromIndexed?.lookupExtension(extensionName);

    ExtensionBuilder extensionBuilder = new SourceExtensionBuilder(
        metadata,
        modifiers,
        extensionName,
        typeVariables,
        type,
        classScope,
        this,
        startOffset,
        nameOffset,
        endOffset,
        referenceFrom);

    constructorReferences.clear();
    Map<String, TypeVariableBuilder> typeVariablesByName =
        checkTypeVariables(typeVariables, extensionBuilder);
    void setParent(String name, MemberBuilder member) {
      while (member != null) {
        member.parent = extensionBuilder;
        member = member.next;
      }
    }

    void setParentAndCheckConflicts(String name, MemberBuilder member) {
      if (typeVariablesByName != null) {
        TypeVariableBuilder tv = typeVariablesByName[name];
        if (tv != null) {
          extensionBuilder.addProblem(
              templateConflictsWithTypeVariable.withArguments(name),
              member.charOffset,
              name.length,
              context: [
                messageConflictsWithTypeVariableCause.withLocation(
                    tv.fileUri, tv.charOffset, name.length)
              ]);
        }
      }
      setParent(name, member);
    }

    members.forEach(setParentAndCheckConflicts);
    constructors.forEach(setParentAndCheckConflicts);
    setters.forEach(setParentAndCheckConflicts);
    addBuilder(extensionName, extensionBuilder, nameOffset,
        getterReference: referenceFrom?.reference);
  }

  TypeBuilder applyMixins(TypeBuilder type, int startCharOffset, int charOffset,
      int charEndOffset, String subclassName, bool isMixinDeclaration,
      {List<MetadataBuilder> metadata,
      String name,
      List<TypeVariableBuilder> typeVariables,
      int modifiers,
      List<TypeBuilder> interfaces}) {
    if (name == null) {
      // The following parameters should only be used when building a named
      // mixin application.
      if (metadata != null) {
        unhandled("metadata", "unnamed mixin application", charOffset, fileUri);
      } else if (interfaces != null) {
        unhandled(
            "interfaces", "unnamed mixin application", charOffset, fileUri);
      }
    }
    if (type is MixinApplicationBuilder) {
      // Documentation below assumes the given mixin application is in one of
      // these forms:
      //
      //     class C extends S with M1, M2, M3;
      //     class Named = S with M1, M2, M3;
      //
      // When we refer to the subclass, we mean `C` or `Named`.

      /// The current supertype.
      ///
      /// Starts out having the value `S` and on each iteration of the loop
      /// below, it will take on the value corresponding to:
      ///
      /// 1. `S with M1`.
      /// 2. `(S with M1) with M2`.
      /// 3. `((S with M1) with M2) with M3`.
      TypeBuilder supertype = type.supertype ?? loader.target.objectType;

      /// The variable part of the mixin application's synthetic name. It
      /// starts out as the name of the superclass, but is only used after it
      /// has been combined with the name of the current mixin. In the examples
      /// from above, it will take these values:
      ///
      /// 1. `S&M1`
      /// 2. `S&M1&M2`
      /// 3. `S&M1&M2&M3`.
      ///
      /// The full name of the mixin application is obtained by prepending the
      /// name of the subclass (`C` or `Named` in the above examples) to the
      /// running name. For the example `C`, that leads to these full names:
      ///
      /// 1. `_C&S&M1`
      /// 2. `_C&S&M1&M2`
      /// 3. `_C&S&M1&M2&M3`.
      ///
      /// For a named mixin application, the last name has been given by the
      /// programmer, so for the example `Named` we see these full names:
      ///
      /// 1. `_Named&S&M1`
      /// 2. `_Named&S&M1&M2`
      /// 3. `Named`.
      String runningName = extractName(supertype.name);

      /// True when we're building a named mixin application. Notice that for
      /// the `Named` example above, this is only true on the last
      /// iteration because only the full mixin application is named.
      bool isNamedMixinApplication;

      /// The names of the type variables of the subclass.
      Set<String> typeVariableNames;
      if (typeVariables != null) {
        typeVariableNames = new Set<String>();
        for (TypeVariableBuilder typeVariable in typeVariables) {
          typeVariableNames.add(typeVariable.name);
        }
      }

      /// Helper function that returns `true` if a type variable with a name
      /// from [typeVariableNames] is referenced in [type].
      bool usesTypeVariables(TypeBuilder type) {
        if (type is NamedTypeBuilder) {
          if (type.declaration is TypeVariableBuilder) {
            return typeVariableNames.contains(type.declaration.name);
          }

          List<TypeBuilder> typeArguments = type.arguments;
          if (typeArguments != null && typeVariables != null) {
            for (TypeBuilder argument in typeArguments) {
              if (usesTypeVariables(argument)) {
                return true;
              }
            }
          }
        } else if (type is FunctionTypeBuilder) {
          if (type.formals != null) {
            for (FormalParameterBuilder formal in type.formals) {
              if (usesTypeVariables(formal.type)) {
                return true;
              }
            }
          }
          List<TypeVariableBuilder> typeVariables = type.typeVariables;
          if (typeVariables != null) {
            for (TypeVariableBuilder variable in typeVariables) {
              if (usesTypeVariables(variable.bound)) {
                return true;
              }
            }
          }
          return usesTypeVariables(type.returnType);
        }
        return false;
      }

      /// Iterate over the mixins from left to right. At the end of each
      /// iteration, a new [supertype] is computed that is the mixin
      /// application of [supertype] with the current mixin.
      for (int i = 0; i < type.mixins.length; i++) {
        TypeBuilder mixin = type.mixins[i];
        isNamedMixinApplication = name != null && mixin == type.mixins.last;
        bool isGeneric = false;
        if (!isNamedMixinApplication) {
          if (supertype is NamedTypeBuilder) {
            isGeneric = isGeneric || usesTypeVariables(supertype);
          }
          if (mixin is NamedTypeBuilder) {
            runningName += "&${extractName(mixin.name)}";
            isGeneric = isGeneric || usesTypeVariables(mixin);
          }
        }
        String fullname =
            isNamedMixinApplication ? name : "_$subclassName&$runningName";
        List<TypeVariableBuilder> applicationTypeVariables;
        List<TypeBuilder> applicationTypeArguments;
        if (isNamedMixinApplication) {
          // If this is a named mixin application, it must be given all the
          // declarated type variables.
          applicationTypeVariables = typeVariables;
        } else {
          // Otherwise, we pass the fresh type variables to the mixin
          // application in the same order as they're declared on the subclass.
          if (isGeneric) {
            this.beginNestedDeclaration(
                TypeParameterScopeKind.unnamedMixinApplication,
                "mixin application");

            applicationTypeVariables = copyTypeVariables(
                typeVariables, currentTypeParameterScopeBuilder);

            List<TypeBuilder> newTypes = <TypeBuilder>[];
            if (supertype is NamedTypeBuilder && supertype.arguments != null) {
              for (int i = 0; i < supertype.arguments.length; ++i) {
                supertype.arguments[i] = supertype.arguments[i].clone(newTypes);
              }
            }
            if (mixin is NamedTypeBuilder && mixin.arguments != null) {
              for (int i = 0; i < mixin.arguments.length; ++i) {
                mixin.arguments[i] = mixin.arguments[i].clone(newTypes);
              }
            }
            for (TypeBuilder newType in newTypes) {
              currentTypeParameterScopeBuilder
                  .addType(new UnresolvedType(newType, -1, null));
            }

            TypeParameterScopeBuilder mixinDeclaration = this
                .endNestedDeclaration(
                    TypeParameterScopeKind.unnamedMixinApplication,
                    "mixin application");
            mixinDeclaration.resolveTypes(applicationTypeVariables, this);

            applicationTypeArguments = <TypeBuilder>[];
            for (TypeVariableBuilder typeVariable in typeVariables) {
              applicationTypeArguments.add(addNamedType(typeVariable.name,
                  const NullabilityBuilder.omitted(), null, charOffset)
                ..bind(
                    // The type variable types passed as arguments to the
                    // generic class representing the anonymous mixin
                    // application should refer back to the type variables of
                    // the class that extend the anonymous mixin application.
                    typeVariable));
            }
          }
        }
        final int computedStartCharOffset =
            (isNamedMixinApplication ? metadata : null) == null
                ? startCharOffset
                : metadata.first.charOffset;

        Class referencesFromClass;
        IndexedClass referencesFromIndexedClass;
        if (referencesFrom != null) {
          referencesFromClass = referencesFromIndexed.lookupClass(fullname);
          referencesFromIndexedClass =
              referencesFromIndexed.lookupIndexedClass(fullname);
        }

        SourceClassBuilder application = new SourceClassBuilder(
          isNamedMixinApplication ? metadata : null,
          isNamedMixinApplication
              ? modifiers | namedMixinApplicationMask
              : abstractMask,
          fullname,
          applicationTypeVariables,
          isMixinDeclaration ? null : supertype,
          isNamedMixinApplication
              ? interfaces
              : isMixinDeclaration
                  ? [supertype, mixin]
                  : null,
          null, // No `on` clause types.
          new Scope(
              local: <String, MemberBuilder>{},
              setters: <String, MemberBuilder>{},
              parent: scope.withTypeVariables(typeVariables),
              debugName: "mixin $fullname ",
              isModifiable: false),
          new ConstructorScope(fullname, <String, MemberBuilder>{}),
          this,
          <ConstructorReferenceBuilder>[],
          computedStartCharOffset,
          charOffset,
          charEndOffset,
          referencesFromClass,
          referencesFromIndexedClass,
          mixedInTypeBuilder: isMixinDeclaration ? null : mixin,
        );
        // TODO(ahe, kmillikin): Should always be true?
        // pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart can't
        // handle that :(
        application.cls.isAnonymousMixin = !isNamedMixinApplication;
        addBuilder(fullname, application, charOffset,
            getterReference: referencesFromClass?.reference);
        supertype = addNamedType(fullname, const NullabilityBuilder.omitted(),
            applicationTypeArguments, charOffset);
      }
      return supertype;
    } else {
      return type;
    }
  }

  void addNamedMixinApplication(
      List<MetadataBuilder> metadata,
      String name,
      List<TypeVariableBuilder> typeVariables,
      int modifiers,
      TypeBuilder mixinApplication,
      List<TypeBuilder> interfaces,
      int startCharOffset,
      int charOffset,
      int charEndOffset) {
    // Nested declaration began in `OutlineBuilder.beginNamedMixinApplication`.
    endNestedDeclaration(TypeParameterScopeKind.namedMixinApplication, name)
        .resolveTypes(typeVariables, this);
    NamedTypeBuilder supertype = applyMixins(mixinApplication, startCharOffset,
        charOffset, charEndOffset, name, false,
        metadata: metadata,
        name: name,
        typeVariables: typeVariables,
        modifiers: modifiers,
        interfaces: interfaces);
    checkTypeVariables(typeVariables, supertype.declaration);
  }

  void addField(
      List<MetadataBuilder> metadata,
      int modifiers,
      bool isTopLevel,
      TypeBuilder type,
      String name,
      int charOffset,
      int charEndOffset,
      Token initializerToken,
      bool hasInitializer,
      {Token constInitializerToken}) {
    if (hasInitializer) {
      modifiers |= hasInitializerMask;
    }
    final bool fieldIsLateWithLowering = (modifiers & lateMask) != 0 &&
        loader.target.backendTarget.isLateFieldLoweringEnabled(
            hasInitializer: hasInitializer,
            isFinal: (modifiers & finalMask) != 0,
            isStatic: isTopLevel || (modifiers & staticMask) != 0);
    final bool isInstanceMember = currentTypeParameterScopeBuilder.kind ==
            TypeParameterScopeKind.classDeclaration &&
        (modifiers & staticMask) == 0;
    String className;
    if (isInstanceMember) {
      className = currentTypeParameterScopeBuilder.name;
    }
    final bool isExtension = currentTypeParameterScopeBuilder.kind ==
        TypeParameterScopeKind.extensionDeclaration;
    String extensionName;
    if (isExtension) {
      extensionName = currentTypeParameterScopeBuilder.name;
    }

    Reference fieldGetterReference;
    Reference fieldSetterReference;
    Reference lateIsSetGetterReference;
    Reference lateIsSetSetterReference;
    Reference lateGetterReference;
    Reference lateSetterReference;
    if (referencesFrom != null) {
      String nameToLookup = SourceFieldBuilder.createFieldName(
          FieldNameType.Field, name,
          isInstanceMember: isInstanceMember,
          className: className,
          isExtensionMethod: isExtension,
          extensionName: extensionName,
          isSynthesized: fieldIsLateWithLowering);
      IndexedContainer indexedContainer =
          _currentClassReferencesFromIndexed ?? referencesFromIndexed;
      Name nameToLookupName = new Name(nameToLookup, indexedContainer.library);
      fieldGetterReference =
          indexedContainer.lookupGetterReference(nameToLookupName);
      fieldSetterReference =
          indexedContainer.lookupSetterReference(nameToLookupName);
      if (fieldIsLateWithLowering) {
        String lateIsSetName = SourceFieldBuilder.createFieldName(
            FieldNameType.IsSetField, name,
            isInstanceMember: isInstanceMember,
            className: className,
            isExtensionMethod: isExtension,
            extensionName: extensionName,
            isSynthesized: fieldIsLateWithLowering);
        Name lateIsSetNameName =
            new Name(lateIsSetName, indexedContainer.library);
        lateIsSetGetterReference =
            indexedContainer.lookupGetterReference(lateIsSetNameName);
        lateIsSetSetterReference =
            indexedContainer.lookupSetterReference(lateIsSetNameName);
        lateGetterReference = indexedContainer.lookupGetterReference(new Name(
            SourceFieldBuilder.createFieldName(FieldNameType.Getter, name,
                isInstanceMember: isInstanceMember,
                className: className,
                isExtensionMethod: isExtension,
                extensionName: extensionName,
                isSynthesized: fieldIsLateWithLowering),
            indexedContainer.library));
        lateSetterReference = indexedContainer.lookupSetterReference(new Name(
            SourceFieldBuilder.createFieldName(FieldNameType.Setter, name,
                isInstanceMember: isInstanceMember,
                className: className,
                isExtensionMethod: isExtension,
                extensionName: extensionName,
                isSynthesized: fieldIsLateWithLowering),
            indexedContainer.library));
      }
    }

    SourceFieldBuilder fieldBuilder = new SourceFieldBuilder(metadata, type,
        name, modifiers, isTopLevel, this, charOffset, charEndOffset,
        fieldGetterReference: fieldGetterReference,
        fieldSetterReference: fieldSetterReference,
        lateIsSetGetterReference: lateIsSetGetterReference,
        lateIsSetSetterReference: lateIsSetSetterReference,
        lateGetterReference: lateGetterReference,
        lateSetterReference: lateSetterReference);
    fieldBuilder.constInitializerToken = constInitializerToken;
    addBuilder(name, fieldBuilder, charOffset,
        getterReference: fieldGetterReference,
        setterReference: fieldSetterReference);
    if (type == null && fieldBuilder.next == null) {
      // Only the first one (the last one in the linked list of next pointers)
      // are added to the tree, had parent pointers and can infer correctly.
      if (initializerToken == null && fieldBuilder.isStatic) {
        // A static field without type and initializer will always be inferred
        // to have type `dynamic`.
        fieldBuilder.fieldType = const DynamicType();
      } else {
        // A field with no type and initializer or an instance field without
        // type and initializer need to have the type inferred.
        fieldBuilder.fieldType =
            new ImplicitFieldType(fieldBuilder, initializerToken);
        registerImplicitlyTypedField(fieldBuilder);
      }
    }
  }

  void addConstructor(
      List<MetadataBuilder> metadata,
      int modifiers,
      TypeBuilder returnType,
      final Object name,
      String constructorName,
      List<TypeVariableBuilder> typeVariables,
      List<FormalParameterBuilder> formals,
      int startCharOffset,
      int charOffset,
      int charOpenParenOffset,
      int charEndOffset,
      String nativeMethodName,
      {Token beginInitializers}) {
    Member referenceFrom;
    if (_currentClassReferencesFromIndexed != null) {
      referenceFrom = _currentClassReferencesFromIndexed.lookupConstructor(
          new Name(
              constructorName, _currentClassReferencesFromIndexed.library));
    }
    ConstructorBuilder constructorBuilder = new ConstructorBuilderImpl(
        metadata,
        modifiers & ~abstractMask,
        returnType,
        constructorName,
        typeVariables,
        formals,
        this,
        startCharOffset,
        charOffset,
        charOpenParenOffset,
        charEndOffset,
        referenceFrom,
        nativeMethodName);
    checkTypeVariables(typeVariables, constructorBuilder);
    addBuilder(constructorName, constructorBuilder, charOffset,
        getterReference: referenceFrom?.reference);
    if (nativeMethodName != null) {
      addNativeMethod(constructorBuilder);
    }
    if (constructorBuilder.isConst) {
      currentTypeParameterScopeBuilder?.declaresConstConstructor = true;
      // const constructors will have their initializers compiled and written
      // into the outline.
      constructorBuilder.beginInitializers =
          beginInitializers ?? new Token.eof(-1);
    }
  }

  void addProcedure(
      List<MetadataBuilder> metadata,
      int modifiers,
      TypeBuilder returnType,
      String name,
      List<TypeVariableBuilder> typeVariables,
      List<FormalParameterBuilder> formals,
      ProcedureKind kind,
      int startCharOffset,
      int charOffset,
      int charOpenParenOffset,
      int charEndOffset,
      String nativeMethodName,
      AsyncMarker asyncModifier,
      {bool isTopLevel,
      bool isExtensionInstanceMember}) {
    assert(isTopLevel != null);
    assert(isExtensionInstanceMember != null);

    if (returnType == null) {
      if (kind == ProcedureKind.Operator &&
          identical(name, indexSetName.text)) {
        returnType = addVoidType(charOffset);
      } else if (kind == ProcedureKind.Setter) {
        returnType = addVoidType(charOffset);
      }
    }
    Reference procedureReference;
    Reference tearOffReference;
    if (referencesFrom != null) {
      if (_currentClassReferencesFromIndexed != null) {
        if (kind == ProcedureKind.Setter) {
          procedureReference =
              _currentClassReferencesFromIndexed.lookupSetterReference(
                  new Name(name, _currentClassReferencesFromIndexed.library));
        } else {
          procedureReference =
              _currentClassReferencesFromIndexed.lookupGetterReference(
                  new Name(name, _currentClassReferencesFromIndexed.library));
        }
      } else {
        if (currentTypeParameterScopeBuilder.kind ==
            TypeParameterScopeKind.extensionDeclaration) {
          bool extensionIsStatic = (modifiers & staticMask) != 0;
          String nameToLookup = SourceProcedureBuilder.createProcedureName(
              true,
              extensionIsStatic,
              kind,
              currentTypeParameterScopeBuilder.name,
              name);
          if (extensionIsStatic && kind == ProcedureKind.Setter) {
            procedureReference = referencesFromIndexed.lookupSetterReference(
                new Name(nameToLookup, referencesFromIndexed.library));
          } else {
            procedureReference = referencesFromIndexed.lookupGetterReference(
                new Name(nameToLookup, referencesFromIndexed.library));
          }
          if (kind == ProcedureKind.Method) {
            String tearOffNameToLookup =
                SourceProcedureBuilder.createProcedureName(
                    true,
                    false,
                    ProcedureKind.Getter,
                    currentTypeParameterScopeBuilder.name,
                    name);
            tearOffReference = referencesFromIndexed.lookupGetterReference(
                new Name(tearOffNameToLookup, referencesFromIndexed.library));
          }
        } else {
          if (kind == ProcedureKind.Setter) {
            procedureReference = referencesFromIndexed.lookupSetterReference(
                new Name(name, referencesFromIndexed.library));
          } else {
            procedureReference = referencesFromIndexed.lookupGetterReference(
                new Name(name, referencesFromIndexed.library));
          }
        }
      }
    }
    ProcedureBuilder procedureBuilder = new SourceProcedureBuilder(
        metadata,
        modifiers,
        returnType,
        name,
        typeVariables,
        formals,
        kind,
        this,
        startCharOffset,
        charOffset,
        charOpenParenOffset,
        charEndOffset,
        procedureReference,
        tearOffReference,
        asyncModifier,
        isExtensionInstanceMember,
        nativeMethodName);
    checkTypeVariables(typeVariables, procedureBuilder);
    addBuilder(name, procedureBuilder, charOffset,
        getterReference: procedureReference);
    if (nativeMethodName != null) {
      addNativeMethod(procedureBuilder);
    }
  }

  void addFactoryMethod(
      List<MetadataBuilder> metadata,
      int modifiers,
      Object name,
      List<FormalParameterBuilder> formals,
      ConstructorReferenceBuilder redirectionTarget,
      int startCharOffset,
      int charOffset,
      int charOpenParenOffset,
      int charEndOffset,
      String nativeMethodName,
      AsyncMarker asyncModifier) {
    TypeBuilder returnType = addNamedType(
        currentTypeParameterScopeBuilder.parent.name,
        const NullabilityBuilder.omitted(),
        <TypeBuilder>[],
        charOffset);
    // Nested declaration began in `OutlineBuilder.beginFactoryMethod`.
    TypeParameterScopeBuilder factoryDeclaration = endNestedDeclaration(
        TypeParameterScopeKind.factoryMethod, "#factory_method");

    // Prepare the simple procedure name.
    String procedureName;
    String constructorName =
        computeAndValidateConstructorName(name, charOffset, isFactory: true);
    if (constructorName != null) {
      procedureName = constructorName;
    } else {
      procedureName = name;
    }

    Reference reference = _currentClassReferencesFromIndexed
        ?.lookupConstructor(
            new Name(procedureName, _currentClassReferencesFromIndexed.library))
        ?.reference;

    ProcedureBuilder procedureBuilder;
    if (redirectionTarget != null) {
      procedureBuilder = new RedirectingFactoryBuilder(
          metadata,
          staticMask | modifiers,
          returnType,
          procedureName,
          copyTypeVariables(
              currentTypeParameterScopeBuilder.typeVariables ??
                  const <TypeVariableBuilder>[],
              factoryDeclaration),
          formals,
          this,
          startCharOffset,
          charOffset,
          charOpenParenOffset,
          charEndOffset,
          reference,
          nativeMethodName,
          redirectionTarget);
    } else {
      procedureBuilder = new SourceProcedureBuilder(
          metadata,
          staticMask | modifiers,
          returnType,
          procedureName,
          copyTypeVariables(
              currentTypeParameterScopeBuilder.typeVariables ??
                  const <TypeVariableBuilder>[],
              factoryDeclaration),
          formals,
          ProcedureKind.Factory,
          this,
          startCharOffset,
          charOffset,
          charOpenParenOffset,
          charEndOffset,
          reference,
          null,
          asyncModifier,
          /* isExtensionInstanceMember = */ false,
          nativeMethodName);
    }

    TypeParameterScopeBuilder savedDeclaration =
        currentTypeParameterScopeBuilder;
    currentTypeParameterScopeBuilder = factoryDeclaration;
    for (TypeVariableBuilder tv in procedureBuilder.typeVariables) {
      NamedTypeBuilder t = procedureBuilder.returnType;
      t.arguments.add(addNamedType(tv.name, const NullabilityBuilder.omitted(),
          null, procedureBuilder.charOffset));
    }
    currentTypeParameterScopeBuilder = savedDeclaration;

    factoryDeclaration.resolveTypes(procedureBuilder.typeVariables, this);
    addBuilder(procedureName, procedureBuilder, charOffset,
        getterReference: reference);
    if (nativeMethodName != null) {
      addNativeMethod(procedureBuilder);
    }
  }

  void addEnum(
      List<MetadataBuilder> metadata,
      String name,
      List<EnumConstantInfo> enumConstantInfos,
      int startCharOffset,
      int charOffset,
      int charEndOffset) {
    Class referencesFromClass;
    IndexedClass referencesFromIndexedClass;
    if (referencesFrom != null) {
      referencesFromClass = referencesFromIndexed.lookupClass(name);
      referencesFromIndexedClass =
          referencesFromIndexed.lookupIndexedClass(name);
    }
    EnumBuilder builder = new EnumBuilder(
        metadata,
        name,
        enumConstantInfos,
        this,
        startCharOffset,
        charOffset,
        charEndOffset,
        referencesFromClass,
        referencesFromIndexedClass);
    addBuilder(name, builder, charOffset,
        getterReference: referencesFromClass?.reference);
  }

  void addFunctionTypeAlias(
      List<MetadataBuilder> metadata,
      String name,
      List<TypeVariableBuilder> typeVariables,
      TypeBuilder type,
      int charOffset) {
    if (typeVariables != null) {
      for (TypeVariableBuilder typeVariable in typeVariables) {
        typeVariable.variance = pendingVariance;
      }
    }
    Typedef referenceFrom = referencesFromIndexed?.lookupTypedef(name);
    TypeAliasBuilder typedefBuilder = new SourceTypeAliasBuilder(
        metadata, name, typeVariables, type, this, charOffset,
        referenceFrom: referenceFrom);
    checkTypeVariables(typeVariables, typedefBuilder);
    // Nested declaration began in `OutlineBuilder.beginFunctionTypeAlias`.
    endNestedDeclaration(TypeParameterScopeKind.typedef, "#typedef")
        .resolveTypes(typeVariables, this);
    addBuilder(name, typedefBuilder, charOffset,
        getterReference: referenceFrom?.reference);
  }

  FunctionTypeBuilder addFunctionType(
      TypeBuilder returnType,
      List<TypeVariableBuilder> typeVariables,
      List<FormalParameterBuilder> formals,
      NullabilityBuilder nullabilityBuilder,
      Uri fileUri,
      int charOffset) {
    FunctionTypeBuilder builder = new FunctionTypeBuilder(returnType,
        typeVariables, formals, nullabilityBuilder, fileUri, charOffset);
    checkTypeVariables(typeVariables, null);
    if (typeVariables != null) {
      for (TypeVariableBuilder builder in typeVariables) {
        if (builder.metadata != null) {
          if (!enableGenericMetadataInLibrary) {
            addProblem(messageAnnotationOnFunctionTypeTypeVariable,
                builder.charOffset, builder.name.length, builder.fileUri);
          }
        }
      }
    }
    // Nested declaration began in `OutlineBuilder.beginFunctionType` or
    // `OutlineBuilder.beginFunctionTypedFormalParameter`.
    endNestedDeclaration(TypeParameterScopeKind.functionType, "#function_type")
        .resolveTypes(typeVariables, this);
    return addType(builder, charOffset);
  }

  FormalParameterBuilder addFormalParameter(
      List<MetadataBuilder> metadata,
      int modifiers,
      TypeBuilder type,
      String name,
      bool hasThis,
      int charOffset,
      Token initializerToken) {
    if (hasThis) {
      modifiers |= initializingFormalMask;
    }
    FormalParameterBuilder formal = new FormalParameterBuilder(
        metadata, modifiers, type, name, this, charOffset,
        fileUri: fileUri)
      ..initializerToken = initializerToken
      ..hasDeclaredInitializer = (initializerToken != null);
    return formal;
  }

  TypeVariableBuilder addTypeVariable(List<MetadataBuilder> metadata,
      String name, TypeBuilder bound, int charOffset, Uri fileUri) {
    TypeVariableBuilder builder = new TypeVariableBuilder(
        name, this, charOffset, fileUri,
        bound: bound, metadata: metadata);
    boundlessTypeVariables.add(builder);
    return builder;
  }

  @override
  void buildOutlineExpressions() {
    MetadataBuilder.buildAnnotations(
        library, metadata, this, null, null, fileUri);
  }

  /// Builds the core AST structures for [declaration] needed for the outline.
  void buildBuilder(Builder declaration, LibraryBuilder coreLibrary) {
    String findDuplicateSuffix(Builder declaration) {
      if (declaration.next != null) {
        int count = 0;
        Builder current = declaration.next;
        while (current != null) {
          count++;
          current = current.next;
        }
        return "#$count";
      }
      return "";
    }

    if (declaration is SourceClassBuilder) {
      Class cls = declaration.build(this, coreLibrary);
      if (!declaration.isPatch) {
        cls.name += findDuplicateSuffix(declaration);
        library.addClass(cls);
      }
    } else if (declaration is SourceExtensionBuilder) {
      Extension extension = declaration.build(this, coreLibrary,
          addMembersToLibrary: !declaration.isDuplicate);
      if (!declaration.isPatch && !declaration.isDuplicate) {
        library.addExtension(extension);
      }
    } else if (declaration is MemberBuilderImpl) {
      declaration.buildMembers(this,
          (Member member, BuiltMemberKind memberKind) {
        if (member is Field) {
          member.isStatic = true;
          if (!declaration.isPatch && !declaration.isDuplicate) {
            library.addField(member);
          }
        } else if (member is Procedure) {
          member.isStatic = true;
          if (!declaration.isPatch &&
              !declaration.isDuplicate &&
              !declaration.isConflictingSetter) {
            library.addProcedure(member);
          }
        } else {
          unhandled("${member.runtimeType}:${memberKind}", "buildBuilder",
              declaration.charOffset, declaration.fileUri);
        }
      });
    } else if (declaration is SourceTypeAliasBuilder) {
      Typedef typedef = declaration.build(this);
      if (!declaration.isPatch && !declaration.isDuplicate) {
        library.addTypedef(typedef);
      }
    } else if (declaration is EnumBuilder) {
      Class cls = declaration.build(this, coreLibrary);
      if (!declaration.isPatch) {
        cls.name += findDuplicateSuffix(declaration);
        library.addClass(cls);
      }
    } else if (declaration is PrefixBuilder) {
      // Ignored. Kernel doesn't represent prefixes.
      return;
    } else if (declaration is BuiltinTypeDeclarationBuilder) {
      // Nothing needed.
      return;
    } else {
      unhandled("${declaration.runtimeType}", "buildBuilder",
          declaration.charOffset, declaration.fileUri);
      return;
    }
  }

  void addNativeDependency(String nativeImportPath) {
    MemberBuilder constructor = loader.getNativeAnnotation();
    Arguments arguments =
        new Arguments(<Expression>[new StringLiteral(nativeImportPath)]);
    Expression annotation;
    if (constructor.isConstructor) {
      annotation = new ConstructorInvocation(constructor.member, arguments)
        ..isConst = true;
    } else {
      annotation = new StaticInvocation(constructor.member, arguments)
        ..isConst = true;
    }
    library.addAnnotation(annotation);
  }

  void addDependencies(Library library, Set<SourceLibraryBuilder> seen) {
    if (!seen.add(this)) {
      return;
    }

    // Merge import and export lists to have the dependencies in source order.
    // This is required for the DietListener to correctly match up metadata.
    int importIndex = 0;
    int exportIndex = 0;
    while (importIndex < imports.length || exportIndex < exports.length) {
      if (exportIndex >= exports.length ||
          (importIndex < imports.length &&
              imports[importIndex].charOffset <
                  exports[exportIndex].charOffset)) {
        // Add import
        Import import = imports[importIndex++];

        // Rather than add a LibraryDependency, we attach an annotation.
        if (import.nativeImportPath != null) {
          addNativeDependency(import.nativeImportPath);
          continue;
        }

        if (import.deferred && import.prefixBuilder?.dependency != null) {
          library.addDependency(import.prefixBuilder.dependency);
        } else {
          library.addDependency(new LibraryDependency.import(
              import.imported.library,
              name: import.prefix,
              combinators: toKernelCombinators(import.combinators))
            ..fileOffset = import.charOffset);
        }
      } else {
        // Add export
        Export export = exports[exportIndex++];
        library.addDependency(new LibraryDependency.export(
            export.exported.library,
            combinators: toKernelCombinators(export.combinators))
          ..fileOffset = export.charOffset);
      }
    }

    for (LibraryBuilder part in parts) {
      if (part is SourceLibraryBuilder) {
        part.addDependencies(library, seen);
      }
    }
  }

  @override
  Builder computeAmbiguousDeclaration(
      String name, Builder declaration, Builder other, int charOffset,
      {bool isExport: false, bool isImport: false}) {
    // TODO(ahe): Can I move this to Scope or Prefix?
    if (declaration == other) return declaration;
    if (declaration is InvalidTypeDeclarationBuilder) return declaration;
    if (other is InvalidTypeDeclarationBuilder) return other;
    if (declaration is AccessErrorBuilder) {
      AccessErrorBuilder error = declaration;
      declaration = error.builder;
    }
    if (other is AccessErrorBuilder) {
      AccessErrorBuilder error = other;
      other = error.builder;
    }
    Builder preferred;
    Uri uri;
    Uri otherUri;
    if (scope.lookupLocalMember(name, setter: false) == declaration) {
      preferred = declaration;
    } else {
      uri = computeLibraryUri(declaration);
      otherUri = computeLibraryUri(other);
      if (declaration is LoadLibraryBuilder) {
        preferred = declaration;
      } else if (other is LoadLibraryBuilder) {
        preferred = other;
      } else if (otherUri?.scheme == "dart" && uri?.scheme != "dart") {
        preferred = declaration;
      } else if (uri?.scheme == "dart" && otherUri?.scheme != "dart") {
        preferred = other;
      }
    }
    if (preferred != null) {
      return preferred;
    }
    if (declaration.next == null && other.next == null) {
      if (isImport && declaration is PrefixBuilder && other is PrefixBuilder) {
        // Handles the case where the same prefix is used for different
        // imports.
        return declaration
          ..exportScope.merge(other.exportScope,
              (String name, Builder existing, Builder member) {
            return computeAmbiguousDeclaration(
                name, existing, member, charOffset,
                isExport: isExport, isImport: isImport);
          });
      }
    }
    if (isExport) {
      Template<Message Function(String name, Uri uri, Uri uri2)> template =
          templateDuplicatedExport;
      Message message = template.withArguments(name, uri, otherUri);
      addProblem(message, charOffset, noLength, fileUri);
    }
    Template<Message Function(String name, Uri uri, Uri uri2)> builderTemplate =
        isExport
            ? templateDuplicatedExportInType
            : templateDuplicatedImportInType;
    Message message = builderTemplate.withArguments(
        name,
        // TODO(ahe): We should probably use a context object here
        // instead of including URIs in this message.
        uri,
        otherUri);
    // We report the error lazily (setting suppressMessage to false) because the
    // spec 18.1 states that 'It is not an error if N is introduced by two or
    // more imports but never referred to.'
    return new InvalidTypeDeclarationBuilder(
        name, message.withLocation(fileUri, charOffset, name.length),
        suppressMessage: false);
  }

  int finishDeferredLoadTearoffs() {
    int total = 0;
    for (Import import in imports) {
      if (import.deferred) {
        Procedure tearoff = import.prefixBuilder.loadLibraryBuilder.tearoff;
        if (tearoff != null) library.addProcedure(tearoff);
        total++;
      }
    }
    return total;
  }

  int finishForwarders() {
    int count = 0;
    CloneVisitorNotMembers cloner = new CloneVisitorNotMembers();
    for (int i = 0; i < forwardersOrigins.length; i += 2) {
      Procedure forwarder = forwardersOrigins[i];
      Procedure origin = forwardersOrigins[i + 1];

      int positionalCount = origin.function.positionalParameters.length;
      if (forwarder.function.positionalParameters.length != positionalCount) {
        return unexpected(
            "$positionalCount",
            "${forwarder.function.positionalParameters.length}",
            origin.fileOffset,
            origin.fileUri);
      }
      for (int j = 0; j < positionalCount; ++j) {
        VariableDeclaration forwarderParameter =
            forwarder.function.positionalParameters[j];
        VariableDeclaration originParameter =
            origin.function.positionalParameters[j];
        if (originParameter.initializer != null) {
          forwarderParameter.initializer =
              cloner.clone(originParameter.initializer);
          forwarderParameter.initializer.parent = forwarderParameter;
        }
      }

      Map<String, VariableDeclaration> originNamedMap =
          <String, VariableDeclaration>{};
      for (VariableDeclaration originNamed in origin.function.namedParameters) {
        originNamedMap[originNamed.name] = originNamed;
      }
      for (VariableDeclaration forwarderNamed
          in forwarder.function.namedParameters) {
        VariableDeclaration originNamed = originNamedMap[forwarderNamed.name];
        if (originNamed == null) {
          return unhandled(
              "null", forwarder.name.text, origin.fileOffset, origin.fileUri);
        }
        if (originNamed.initializer == null) continue;
        forwarderNamed.initializer = cloner.clone(originNamed.initializer);
        forwarderNamed.initializer.parent = forwarderNamed;
      }

      ++count;
    }
    forwardersOrigins.clear();
    return count;
  }

  void addNativeMethod(FunctionBuilder method) {
    nativeMethods.add(method);
  }

  int finishNativeMethods() {
    for (FunctionBuilder method in nativeMethods) {
      method.becomeNative(loader);
    }
    return nativeMethods.length;
  }

  /// Creates a copy of [original] into the scope of [declaration].
  ///
  /// This is used for adding copies of class type parameters to factory
  /// methods and unnamed mixin applications, and for adding copies of
  /// extension type parameters to extension instance methods.
  ///
  /// If [synthesizeTypeParameterNames] is `true` the names of the
  /// [TypeParameter] are prefix with '#' to indicate that their synthesized.
  List<TypeVariableBuilder> copyTypeVariables(
      List<TypeVariableBuilder> original, TypeParameterScopeBuilder declaration,
      {bool isExtensionTypeParameter: false}) {
    List<TypeBuilder> newTypes = <TypeBuilder>[];
    List<TypeVariableBuilder> copy = <TypeVariableBuilder>[];
    for (TypeVariableBuilder variable in original) {
      TypeVariableBuilder newVariable = new TypeVariableBuilder(
          variable.name, this, variable.charOffset, variable.fileUri,
          bound: variable.bound?.clone(newTypes),
          isExtensionTypeParameter: isExtensionTypeParameter,
          variableVariance:
              variable.parameter.isLegacyCovariant ? null : variable.variance);
      copy.add(newVariable);
      boundlessTypeVariables.add(newVariable);
    }
    for (TypeBuilder newType in newTypes) {
      declaration.addType(new UnresolvedType(newType, -1, null));
    }
    return copy;
  }

  int finishTypeVariables(ClassBuilder object, TypeBuilder dynamicType) {
    int count = boundlessTypeVariables.length;
    // Ensure that type parameters are built after their dependencies by sorting
    // them topologically using references in bounds.
    for (TypeVariableBuilder builder
        in _sortTypeVariablesTopologically(boundlessTypeVariables)) {
      builder.finish(this, object, dynamicType);
    }
    boundlessTypeVariables.clear();

    processPendingNullabilities();

    return count;
  }

  /// Assigns nullabilities to types in [_pendingNullabilities].
  ///
  /// It's a helper function to assign the nullabilities to type-parameter types
  /// after the corresponding type parameters have their bounds set or changed.
  /// The function takes into account that some of the types in the input list
  /// may be bounds to some of the type parameters of other types from the input
  /// list.
  void processPendingNullabilities() {
    // The bounds of type parameters may be type-parameter types of other
    // parameters from the same declaration.  In this case we need to set the
    // nullability for them first.  To preserve the ordering, we implement a
    // depth-first search over the types.  We use the fact that a nullability
    // of a type parameter type can't ever be 'nullable' if computed from the
    // bound. It allows us to use 'nullable' nullability as the marker in the
    // DFS implementation.
    Nullability marker = Nullability.nullable;
    List<TypeParameterType> stack =
        new List<TypeParameterType>.filled(_pendingNullabilities.length, null);
    int stackTop = 0;
    for (PendingNullability pendingNullability in _pendingNullabilities) {
      pendingNullability.type.declaredNullability = null;
    }
    for (PendingNullability pendingNullability in _pendingNullabilities) {
      TypeParameterType type = pendingNullability.type;
      if (type.declaredNullability != null) {
        // Nullability for [type] was already computed on one of the branches
        // of the depth-first search.  Continue to the next one.
        continue;
      }
      if (type.parameter.bound is TypeParameterType) {
        TypeParameterType current = type;
        TypeParameterType next = current.parameter.bound;
        while (next != null && next.declaredNullability == null) {
          stack[stackTop++] = current;
          current.declaredNullability = marker;

          current = next;
          if (current.parameter.bound is TypeParameterType) {
            next = current.parameter.bound;
            if (next.declaredNullability == marker) {
              next.declaredNullability = Nullability.undetermined;
              current.parameter.bound = const InvalidType();
              current.parameter.defaultType = const InvalidType();
              addProblem(
                  templateCycleInTypeVariables.withArguments(
                      next.parameter.name, current.parameter.name),
                  pendingNullability.charOffset,
                  next.parameter.name.length,
                  pendingNullability.fileUri);
              next = null;
            }
          } else {
            next = null;
          }
        }
        current.declaredNullability =
            TypeParameterType.computeNullabilityFromBound(current.parameter);
        while (stackTop != 0) {
          --stackTop;
          current = stack[stackTop];
          current.declaredNullability =
              TypeParameterType.computeNullabilityFromBound(current.parameter);
        }
      } else {
        type.declaredNullability =
            TypeParameterType.computeNullabilityFromBound(type.parameter);
      }
    }
    _pendingNullabilities.clear();
  }

  int computeVariances() {
    int count = 0;
    for (Builder declaration in libraryDeclaration.members.values) {
      while (declaration != null) {
        if (declaration is TypeAliasBuilder &&
            declaration.typeVariablesCount > 0) {
          for (TypeVariableBuilder typeParameter in declaration.typeVariables) {
            typeParameter.variance = computeTypeVariableBuilderVariance(
                typeParameter, declaration.type, this);
            ++count;
          }
        }
        declaration = declaration.next;
      }
    }
    return count;
  }

  int computeDefaultTypes(TypeBuilder dynamicType, TypeBuilder nullType,
      TypeBuilder bottomType, ClassBuilder objectClass) {
    int count = 0;

    int computeDefaultTypesForVariables(List<TypeVariableBuilder> variables,
        {bool inErrorRecovery}) {
      if (variables == null) return 0;

      bool haveErroneousBounds = false;
      if (!inErrorRecovery) {
        if (!enableGenericMetadataInLibrary) {
          for (int i = 0; i < variables.length; ++i) {
            TypeVariableBuilder variable = variables[i];
            List<TypeBuilder> genericFunctionTypes = <TypeBuilder>[];
            findGenericFunctionTypes(variable.bound,
                result: genericFunctionTypes);
            if (genericFunctionTypes.length > 0) {
              haveErroneousBounds = true;
              addProblem(messageGenericFunctionTypeInBound, variable.charOffset,
                  variable.name.length, variable.fileUri);
            }
          }
        }

        if (!haveErroneousBounds) {
          List<TypeBuilder> unboundTypes = [];
          List<TypeVariableBuilder> unboundTypeVariables = [];
          List<TypeBuilder> calculatedBounds = calculateBounds(
              variables,
              dynamicType,
              isNonNullableByDefault ? bottomType : nullType,
              objectClass,
              unboundTypes: unboundTypes,
              unboundTypeVariables: unboundTypeVariables);
          for (TypeBuilder unboundType in unboundTypes) {
            currentTypeParameterScopeBuilder
                .addType(new UnresolvedType(unboundType, -1, null));
          }
          boundlessTypeVariables.addAll(unboundTypeVariables);
          for (int i = 0; i < variables.length; ++i) {
            variables[i].defaultType = calculatedBounds[i];
          }
        }
      }

      if (inErrorRecovery || haveErroneousBounds) {
        // Use dynamic in case of errors.
        for (int i = 0; i < variables.length; ++i) {
          variables[i].defaultType = dynamicType;
        }
      }

      return variables.length;
    }

    void reportIssues(List<Object> issues) {
      for (int i = 0; i < issues.length; i += 3) {
        TypeDeclarationBuilder declaration = issues[i];
        Message message = issues[i + 1];
        List<LocatedMessage> context = issues[i + 2];

        addProblem(message, declaration.charOffset, declaration.name.length,
            declaration.fileUri,
            context: context);
      }
    }

    for (Builder declaration in libraryDeclaration.members.values) {
      if (declaration is ClassBuilder) {
        {
          List<Object> issues = getNonSimplicityIssuesForDeclaration(
              declaration,
              performErrorRecovery: true);
          reportIssues(issues);
          count += computeDefaultTypesForVariables(declaration.typeVariables,
              inErrorRecovery: issues.isNotEmpty);

          declaration.constructors.forEach((String name, Builder member) {
            List<FormalParameterBuilder> formals;
            if (member is ProcedureBuilder) {
              assert(member.isFactory,
                  "Unexpected constructor member (${member.runtimeType}).");
              count += computeDefaultTypesForVariables(member.typeVariables,
                  // Type variables are inherited from the class so if the class
                  // has issues, so does the factory constructors.
                  inErrorRecovery: issues.isNotEmpty);
              formals = member.formals;
            } else {
              assert(member is ConstructorBuilder,
                  "Unexpected constructor member (${member.runtimeType}).");
              formals = (member as ConstructorBuilder).formals;
            }
            if (formals != null && formals.isNotEmpty) {
              for (FormalParameterBuilder formal in formals) {
                List<Object> issues =
                    getInboundReferenceIssuesInType(formal.type);
                reportIssues(issues);
              }
            }
          });
        }
        declaration.forEach((String name, Builder member) {
          if (member is ProcedureBuilder) {
            List<Object> issues =
                getNonSimplicityIssuesForTypeVariables(member.typeVariables);
            if (member.formals != null && member.formals.isNotEmpty) {
              for (FormalParameterBuilder formal in member.formals) {
                issues.addAll(getInboundReferenceIssuesInType(formal.type));
              }
            }
            if (member.returnType != null) {
              issues.addAll(getInboundReferenceIssuesInType(member.returnType));
            }
            reportIssues(issues);
            count += computeDefaultTypesForVariables(member.typeVariables,
                inErrorRecovery: issues.isNotEmpty);
          } else {
            assert(member is FieldBuilder,
                "Unexpected class member $member (${member.runtimeType}).");
            TypeBuilder fieldType = (member as FieldBuilder).type;
            if (fieldType != null) {
              List<Object> issues = getInboundReferenceIssuesInType(fieldType);
              reportIssues(issues);
            }
          }
        });
      } else if (declaration is TypeAliasBuilder) {
        List<Object> issues = getNonSimplicityIssuesForDeclaration(declaration,
            performErrorRecovery: true);
        issues.addAll(getInboundReferenceIssuesInType(declaration.type));
        reportIssues(issues);
        count += computeDefaultTypesForVariables(declaration.typeVariables,
            inErrorRecovery: issues.isNotEmpty);
      } else if (declaration is FunctionBuilder) {
        List<Object> issues =
            getNonSimplicityIssuesForTypeVariables(declaration.typeVariables);
        if (declaration.formals != null && declaration.formals.isNotEmpty) {
          for (FormalParameterBuilder formal in declaration.formals) {
            issues.addAll(getInboundReferenceIssuesInType(formal.type));
          }
        }
        if (declaration.returnType != null) {
          issues
              .addAll(getInboundReferenceIssuesInType(declaration.returnType));
        }
        reportIssues(issues);
        count += computeDefaultTypesForVariables(declaration.typeVariables,
            inErrorRecovery: issues.isNotEmpty);
      } else if (declaration is ExtensionBuilder) {
        {
          List<Object> issues = getNonSimplicityIssuesForDeclaration(
              declaration,
              performErrorRecovery: true);
          reportIssues(issues);
          count += computeDefaultTypesForVariables(declaration.typeParameters,
              inErrorRecovery: issues.isNotEmpty);
        }
        declaration.forEach((String name, Builder member) {
          if (member is ProcedureBuilder) {
            List<Object> issues =
                getNonSimplicityIssuesForTypeVariables(member.typeVariables);
            if (member.formals != null && member.formals.isNotEmpty) {
              for (FormalParameterBuilder formal in member.formals) {
                issues.addAll(getInboundReferenceIssuesInType(formal.type));
              }
            }
            if (member.returnType != null) {
              issues.addAll(getInboundReferenceIssuesInType(member.returnType));
            }
            reportIssues(issues);
            count += computeDefaultTypesForVariables(member.typeVariables,
                inErrorRecovery: issues.isNotEmpty);
          } else {
            assert(member is FieldBuilder,
                "Unexpected extension member $member (${member.runtimeType}).");
          }
        });
      } else if (declaration is FieldBuilder) {
        if (declaration.type != null) {
          List<Object> issues =
              getInboundReferenceIssuesInType(declaration.type);
          reportIssues(issues);
        }
      } else {
        assert(
            declaration is PrefixBuilder ||
                declaration is DynamicTypeDeclarationBuilder ||
                declaration is NeverTypeDeclarationBuilder,
            "Unexpected top level member $declaration "
            "(${declaration.runtimeType}).");
      }
    }
    for (Builder declaration in libraryDeclaration.setters.values) {
      assert(
          declaration is ProcedureBuilder,
          "Expected setter to be a ProcedureBuilder, "
          "but got '${declaration.runtimeType}'");
      if (declaration is ProcedureBuilder &&
          declaration.formals != null &&
          declaration.formals.isNotEmpty) {
        for (FormalParameterBuilder formal in declaration.formals) {
          reportIssues(getInboundReferenceIssuesInType(formal.type));
        }
      }
    }

    return count;
  }

  @override
  void applyPatches() {
    if (!isPatch) return;

    if (languageVersion != origin.languageVersion) {
      List<LocatedMessage> context = <LocatedMessage>[];
      if (origin.languageVersion.isExplicit) {
        context.add(messageLanguageVersionLibraryContext.withLocation(
            origin.languageVersion.fileUri,
            origin.languageVersion.charOffset,
            origin.languageVersion.charCount));
      }

      if (languageVersion.isExplicit) {
        addProblem(
            messageLanguageVersionMismatchInPatch,
            languageVersion.charOffset,
            languageVersion.charCount,
            languageVersion.fileUri,
            context: context);
      } else {
        addProblem(messageLanguageVersionMismatchInPatch, -1, noLength, fileUri,
            context: context);
      }
    }

    NameIterator originDeclarations = origin.nameIterator;
    while (originDeclarations.moveNext()) {
      String name = originDeclarations.name;
      Builder member = originDeclarations.current;
      bool isSetter = member.isSetter;
      Builder patch = scope.lookupLocalMember(name, setter: isSetter);
      if (patch != null) {
        // [patch] has the same name as a [member] in [origin] library, so it
        // must be a patch to [member].
        member.applyPatch(patch);
        // TODO(ahe): Verify that patch has the @patch annotation.
      } else {
        // No member with [name] exists in this library already. So we need to
        // import it into the patch library. This ensures that the origin
        // library is in scope of the patch library.
        if (isSetter) {
          scopeBuilder.addSetter(name, member);
        } else {
          scopeBuilder.addMember(name, member);
        }
      }
    }
    NameIterator patchDeclarations = nameIterator;
    while (patchDeclarations.moveNext()) {
      String name = patchDeclarations.name;
      Builder member = patchDeclarations.current;
      // We need to inject all non-patch members into the origin library. This
      // should only apply to private members.
      if (member.isPatch) {
        // Ignore patches.
      } else if (name.startsWith("_")) {
        origin.injectMemberFromPatch(name, member);
      } else {
        origin.exportMemberFromPatch(name, member);
      }
    }
  }

  int finishPatchMethods() {
    if (!isPatch) return 0;
    int count = 0;
    Iterator<Builder> iterator = this.iterator;
    while (iterator.moveNext()) {
      count += iterator.current.finishPatch();
    }
    return count;
  }

  void injectMemberFromPatch(String name, Builder member) {
    if (member.isSetter) {
      assert(scope.lookupLocalMember(name, setter: true) == null);
      scopeBuilder.addSetter(name, member);
    } else {
      assert(scope.lookupLocalMember(name, setter: false) == null);
      scopeBuilder.addMember(name, member);
    }
  }

  void exportMemberFromPatch(String name, Builder member) {
    if (importUri.scheme != "dart" || !importUri.path.startsWith("_")) {
      addProblem(templatePatchInjectionFailed.withArguments(name, importUri),
          member.charOffset, noLength, member.fileUri);
    }
    // Platform-private libraries, such as "dart:_internal" have special
    // semantics: public members are injected into the origin library.
    // TODO(ahe): See if we can remove this special case.

    // If this member already exist in the origin library scope, it should
    // have been marked as patch.
    assert((member.isSetter &&
            scope.lookupLocalMember(name, setter: true) == null) ||
        (!member.isSetter &&
            scope.lookupLocalMember(name, setter: false) == null));
    addToExportScope(name, member);
  }

  void reportTypeArgumentIssues(
      Iterable<TypeArgumentIssue> issues, Uri fileUri, int offset,
      {bool inferred,
      TypeArgumentsInfo typeArgumentsInfo,
      DartType targetReceiver,
      String targetName}) {
    for (TypeArgumentIssue issue in issues) {
      DartType argument = issue.argument;
      TypeParameter typeParameter = issue.typeParameter;

      Message message;
      bool issueInferred = inferred ??
          typeArgumentsInfo?.isInferred(issue.index) ??
          inferredTypes.contains(argument);
      offset =
          typeArgumentsInfo?.getOffsetForIndex(issue.index, offset) ?? offset;
      if (issue.isGenericTypeAsArgumentIssue) {
        if (issueInferred) {
          message = templateGenericFunctionTypeInferredAsActualTypeArgument
              .withArguments(argument, isNonNullableByDefault);
        } else {
          message = messageGenericFunctionTypeUsedAsActualTypeArgument;
        }
        typeParameter = null;
      } else {
        if (issue.enclosingType == null && targetReceiver != null) {
          if (issueInferred) {
            message =
                templateIncorrectTypeArgumentQualifiedInferred.withArguments(
                    argument,
                    typeParameter.bound,
                    typeParameter.name,
                    targetReceiver,
                    targetName,
                    isNonNullableByDefault);
          } else {
            message = templateIncorrectTypeArgumentQualified.withArguments(
                argument,
                typeParameter.bound,
                typeParameter.name,
                targetReceiver,
                targetName,
                isNonNullableByDefault);
          }
        } else {
          String enclosingName = issue.enclosingType == null
              ? targetName
              : getGenericTypeName(issue.enclosingType);
          assert(enclosingName != null);
          if (issueInferred) {
            message = templateIncorrectTypeArgumentInferred.withArguments(
                argument,
                typeParameter.bound,
                typeParameter.name,
                enclosingName,
                isNonNullableByDefault);
          } else {
            message = templateIncorrectTypeArgument.withArguments(
                argument,
                typeParameter.bound,
                typeParameter.name,
                enclosingName,
                isNonNullableByDefault);
          }
        }
      }

      // Don't show the hint about an attempted super-bounded type if the issue
      // with the argument is that it's generic.
      reportTypeArgumentIssue(message, fileUri, offset,
          typeParameter: typeParameter,
          superBoundedAttempt:
              issue.isGenericTypeAsArgumentIssue ? null : issue.enclosingType,
          superBoundedAttemptInverted:
              issue.isGenericTypeAsArgumentIssue ? null : issue.invertedType);
    }
  }

  void reportTypeArgumentIssue(Message message, Uri fileUri, int fileOffset,
      {TypeParameter typeParameter,
      DartType superBoundedAttempt,
      DartType superBoundedAttemptInverted}) {
    List<LocatedMessage> context;
    // Skip reporting location for function-type type parameters as it's a
    // limitation of Kernel.
    if (typeParameter != null &&
        typeParameter.fileOffset != -1 &&
        typeParameter.location != null) {
      // It looks like when parameters come from patch files, they don't
      // have a reportable location.
      (context ??= <LocatedMessage>[]).add(
          messageIncorrectTypeArgumentVariable.withLocation(
              typeParameter.location.file, typeParameter.fileOffset, noLength));
    }
    if (superBoundedAttemptInverted != null && superBoundedAttempt != null) {
      (context ??= <LocatedMessage>[]).add(templateSuperBoundedHint
          .withArguments(superBoundedAttempt, superBoundedAttemptInverted,
              isNonNullableByDefault)
          .withLocation(fileUri, fileOffset, noLength));
    }
    addProblem(message, fileOffset, noLength, fileUri, context: context);
  }

  void checkTypesInField(
      FieldBuilder fieldBuilder, TypeEnvironment typeEnvironment) {
    // Check the bounds in the field's type.
    checkBoundsInType(fieldBuilder.fieldType, typeEnvironment,
        fieldBuilder.fileUri, fieldBuilder.charOffset,
        allowSuperBounded: true);

    // Check that the field has an initializer if its type is potentially
    // non-nullable.
    if (isNonNullableByDefault) {
      // Only static and top-level fields are checked here.  Instance fields are
      // checked elsewhere.
      DartType fieldType = fieldBuilder.fieldType;
      if (!fieldBuilder.isDeclarationInstanceMember &&
          !fieldBuilder.isLate &&
          !fieldBuilder.isExternal &&
          fieldType is! InvalidType &&
          fieldType.isPotentiallyNonNullable &&
          !fieldBuilder.hasInitializer) {
        addProblem(
            templateFieldNonNullableWithoutInitializerError.withArguments(
                fieldBuilder.name,
                fieldBuilder.fieldType,
                isNonNullableByDefault),
            fieldBuilder.charOffset,
            fieldBuilder.name.length,
            fieldBuilder.fileUri);
      }
    }
  }

  void checkInitializersInFormals(
      List<FormalParameterBuilder> formals, TypeEnvironment typeEnvironment) {
    if (!isNonNullableByDefault) return;

    for (FormalParameterBuilder formal in formals) {
      bool isOptionalPositional = formal.isOptional && formal.isPositional;
      bool isOptionalNamed = !formal.isNamedRequired && formal.isNamed;
      bool isOptional = isOptionalPositional || isOptionalNamed;
      if (isOptional &&
          formal.variable.type.isPotentiallyNonNullable &&
          !formal.hasDeclaredInitializer) {
        addProblem(
            templateOptionalNonNullableWithoutInitializerError.withArguments(
                formal.name, formal.variable.type, isNonNullableByDefault),
            formal.charOffset,
            formal.name.length,
            formal.fileUri);
      }
    }
  }

  void checkBoundsInTypeParameters(TypeEnvironment typeEnvironment,
      List<TypeParameter> typeParameters, Uri fileUri) {
    // Check in bounds of own type variables.
    for (TypeParameter parameter in typeParameters) {
      List<TypeArgumentIssue> issues = findTypeArgumentIssues(
          parameter.bound,
          typeEnvironment,
          isNonNullableByDefault
              ? SubtypeCheckMode.withNullabilities
              : SubtypeCheckMode.ignoringNullabilities,
          allowSuperBounded: true,
          isNonNullableByDefault: library.isNonNullableByDefault,
          areGenericArgumentsAllowed: enableGenericMetadataInLibrary);
      for (TypeArgumentIssue issue in issues) {
        DartType argument = issue.argument;
        TypeParameter typeParameter = issue.typeParameter;
        if (inferredTypes.contains(argument)) {
          // Inference in type expressions in the supertypes boils down to
          // instantiate-to-bound which shouldn't produce anything that breaks
          // the bounds after the non-simplicity checks are done.  So, any
          // violation here is the result of non-simple bounds, and the error
          // is reported elsewhere.
          continue;
        }

        if (issue.isGenericTypeAsArgumentIssue) {
          reportTypeArgumentIssue(
              messageGenericFunctionTypeUsedAsActualTypeArgument,
              fileUri,
              parameter.fileOffset,
              typeParameter: null);
        } else {
          reportTypeArgumentIssue(
              templateIncorrectTypeArgument.withArguments(
                  argument,
                  typeParameter.bound,
                  typeParameter.name,
                  getGenericTypeName(issue.enclosingType),
                  library.isNonNullableByDefault),
              fileUri,
              parameter.fileOffset,
              typeParameter: typeParameter,
              superBoundedAttempt: issue.enclosingType,
              superBoundedAttemptInverted: issue.invertedType);
        }
      }
    }
  }

  void checkBoundsInFunctionNodeParts(
      TypeEnvironment typeEnvironment, Uri fileUri, int fileOffset,
      {List<TypeParameter> typeParameters,
      List<VariableDeclaration> positionalParameters,
      List<VariableDeclaration> namedParameters,
      DartType returnType,
      int requiredParameterCount,
      bool skipReturnType = false}) {
    if (typeParameters != null) {
      for (TypeParameter parameter in typeParameters) {
        checkBoundsInType(
            parameter.bound, typeEnvironment, fileUri, parameter.fileOffset,
            allowSuperBounded: true);
      }
    }
    if (positionalParameters != null) {
      for (int i = 0; i < positionalParameters.length; ++i) {
        VariableDeclaration parameter = positionalParameters[i];
        checkBoundsInType(
            parameter.type, typeEnvironment, fileUri, parameter.fileOffset,
            allowSuperBounded: true);
      }
    }
    if (namedParameters != null) {
      for (int i = 0; i < namedParameters.length; ++i) {
        VariableDeclaration named = namedParameters[i];
        checkBoundsInType(
            named.type, typeEnvironment, fileUri, named.fileOffset,
            allowSuperBounded: true);
      }
    }
    if (!skipReturnType && returnType != null) {
      List<TypeArgumentIssue> issues = findTypeArgumentIssues(
          returnType,
          typeEnvironment,
          isNonNullableByDefault
              ? SubtypeCheckMode.withNullabilities
              : SubtypeCheckMode.ignoringNullabilities,
          allowSuperBounded: true,
          isNonNullableByDefault: library.isNonNullableByDefault,
          areGenericArgumentsAllowed: enableGenericMetadataInLibrary);
      for (TypeArgumentIssue issue in issues) {
        DartType argument = issue.argument;
        TypeParameter typeParameter = issue.typeParameter;

        // We don't need to check if [argument] was inferred or specified
        // here, because inference in return types boils down to instantiate-
        // -to-bound, and it can't provide a type that violates the bound.
        if (issue.isGenericTypeAsArgumentIssue) {
          reportTypeArgumentIssue(
              messageGenericFunctionTypeUsedAsActualTypeArgument,
              fileUri,
              fileOffset,
              typeParameter: null);
        } else {
          reportTypeArgumentIssue(
              templateIncorrectTypeArgumentInReturnType.withArguments(
                  argument,
                  typeParameter.bound,
                  typeParameter.name,
                  getGenericTypeName(issue.enclosingType),
                  isNonNullableByDefault),
              fileUri,
              fileOffset,
              typeParameter: typeParameter,
              superBoundedAttempt: issue.enclosingType,
              superBoundedAttemptInverted: issue.invertedType);
        }
      }
    }
  }

  void checkTypesInProcedureBuilder(
      ProcedureBuilder procedureBuilder, TypeEnvironment typeEnvironment) {
    checkBoundsInFunctionNode(procedureBuilder.procedure.function,
        typeEnvironment, procedureBuilder.fileUri);
    if (procedureBuilder.formals != null &&
        !(procedureBuilder.isAbstract || procedureBuilder.isExternal)) {
      checkInitializersInFormals(procedureBuilder.formals, typeEnvironment);
    }
  }

  void checkTypesInConstructorBuilder(
      ConstructorBuilder constructorBuilder, TypeEnvironment typeEnvironment) {
    checkBoundsInFunctionNode(
        constructorBuilder.constructor.function, typeEnvironment, fileUri);
    if (!constructorBuilder.isExternal && constructorBuilder.formals != null) {
      checkInitializersInFormals(constructorBuilder.formals, typeEnvironment);
    }
  }

  void checkTypesInRedirectingFactoryBuilder(
      RedirectingFactoryBuilder redirectingFactoryBuilder,
      TypeEnvironment typeEnvironment) {
    checkBoundsInFunctionNode(redirectingFactoryBuilder.procedure.function,
        typeEnvironment, redirectingFactoryBuilder.fileUri);
    // Default values are not required on redirecting factory constructors so
    // we don't call [checkInitializersInFormals].
  }

  void checkBoundsInFunctionNode(
      FunctionNode function, TypeEnvironment typeEnvironment, Uri fileUri,
      {bool skipReturnType = false}) {
    checkBoundsInFunctionNodeParts(
        typeEnvironment, fileUri, function.fileOffset,
        typeParameters: function.typeParameters,
        positionalParameters: function.positionalParameters,
        namedParameters: function.namedParameters,
        returnType: function.returnType,
        requiredParameterCount: function.requiredParameterCount,
        skipReturnType: skipReturnType);
  }

  void checkBoundsInListLiteral(
      ListLiteral node, TypeEnvironment typeEnvironment, Uri fileUri,
      {bool inferred = false}) {
    checkBoundsInType(
        node.typeArgument, typeEnvironment, fileUri, node.fileOffset,
        inferred: inferred, allowSuperBounded: true);
  }

  void checkBoundsInSetLiteral(
      SetLiteral node, TypeEnvironment typeEnvironment, Uri fileUri,
      {bool inferred = false}) {
    checkBoundsInType(
        node.typeArgument, typeEnvironment, fileUri, node.fileOffset,
        inferred: inferred, allowSuperBounded: true);
  }

  void checkBoundsInMapLiteral(
      MapLiteral node, TypeEnvironment typeEnvironment, Uri fileUri,
      {bool inferred = false}) {
    checkBoundsInType(node.keyType, typeEnvironment, fileUri, node.fileOffset,
        inferred: inferred, allowSuperBounded: true);
    checkBoundsInType(node.valueType, typeEnvironment, fileUri, node.fileOffset,
        inferred: inferred, allowSuperBounded: true);
  }

  void checkBoundsInType(
      DartType type, TypeEnvironment typeEnvironment, Uri fileUri, int offset,
      {bool inferred, bool allowSuperBounded = true}) {
    List<TypeArgumentIssue> issues = findTypeArgumentIssues(
        type,
        typeEnvironment,
        isNonNullableByDefault
            ? SubtypeCheckMode.withNullabilities
            : SubtypeCheckMode.ignoringNullabilities,
        allowSuperBounded: allowSuperBounded,
        isNonNullableByDefault: library.isNonNullableByDefault,
        areGenericArgumentsAllowed: enableGenericMetadataInLibrary);
    reportTypeArgumentIssues(issues, fileUri, offset, inferred: inferred);
  }

  void checkBoundsInVariableDeclaration(
      VariableDeclaration node, TypeEnvironment typeEnvironment, Uri fileUri,
      {bool inferred = false}) {
    if (node.type == null) return;
    checkBoundsInType(node.type, typeEnvironment, fileUri, node.fileOffset,
        inferred: inferred, allowSuperBounded: true);
  }

  void checkBoundsInConstructorInvocation(
      ConstructorInvocation node, TypeEnvironment typeEnvironment, Uri fileUri,
      {bool inferred = false}) {
    if (node.arguments.types.isEmpty) return;
    Constructor constructor = node.target;
    Class klass = constructor.enclosingClass;
    DartType constructedType = new InterfaceType(
        klass, klass.enclosingLibrary.nonNullable, node.arguments.types);
    checkBoundsInType(
        constructedType, typeEnvironment, fileUri, node.fileOffset,
        inferred: inferred, allowSuperBounded: false);
  }

  void checkBoundsInFactoryInvocation(
      StaticInvocation node, TypeEnvironment typeEnvironment, Uri fileUri,
      {bool inferred = false}) {
    if (node.arguments.types.isEmpty) return;
    Procedure factory = node.target;
    assert(factory.isFactory);
    Class klass = factory.enclosingClass;
    DartType constructedType = new InterfaceType(
        klass, klass.enclosingLibrary.nonNullable, node.arguments.types);
    checkBoundsInType(
        constructedType, typeEnvironment, fileUri, node.fileOffset,
        inferred: inferred, allowSuperBounded: false);
  }

  void checkBoundsInStaticInvocation(
      StaticInvocation node,
      TypeEnvironment typeEnvironment,
      Uri fileUri,
      TypeArgumentsInfo typeArgumentsInfo) {
    // TODO(johnniwinther): Handle partially inferred type arguments in
    // extension method calls. Currently all are considered inferred in the
    // error messages.
    if (node.arguments.types.isEmpty) return;
    Class klass = node.target.enclosingClass;
    List<TypeParameter> parameters = node.target.function.typeParameters;
    List<DartType> arguments = node.arguments.types;
    // The following error is to be reported elsewhere.
    if (parameters.length != arguments.length) return;

    final DartType bottomType = isNonNullableByDefault
        ? const NeverType.nonNullable()
        : const NullType();
    List<TypeArgumentIssue> issues = findTypeArgumentIssuesForInvocation(
        parameters,
        arguments,
        typeEnvironment,
        isNonNullableByDefault
            ? SubtypeCheckMode.withNullabilities
            : SubtypeCheckMode.ignoringNullabilities,
        bottomType,
        isNonNullableByDefault: library.isNonNullableByDefault,
        areGenericArgumentsAllowed: enableGenericMetadataInLibrary);
    if (issues.isNotEmpty) {
      DartType targetReceiver;
      if (klass != null) {
        targetReceiver =
            new InterfaceType(klass, klass.enclosingLibrary.nonNullable);
      }
      String targetName = node.target.name.text;
      reportTypeArgumentIssues(issues, fileUri, node.fileOffset,
          typeArgumentsInfo: typeArgumentsInfo,
          targetReceiver: targetReceiver,
          targetName: targetName);
    }
  }

  void checkBoundsInMethodInvocation(
      DartType receiverType,
      TypeEnvironment typeEnvironment,
      ClassHierarchy hierarchy,
      TypeInferrerImpl typeInferrer,
      Name name,
      Member interfaceTarget,
      Arguments arguments,
      Uri fileUri,
      int offset) {
    if (arguments.types.isEmpty) return;
    Class klass;
    List<DartType> receiverTypeArguments;
    if (receiverType is InterfaceType) {
      klass = receiverType.classNode;
      receiverTypeArguments = receiverType.typeArguments;
    } else {
      return;
    }
    // TODO(dmitryas): Find a better way than relying on [interfaceTarget].
    Member method = hierarchy.getDispatchTarget(klass, name) ?? interfaceTarget;
    if (method == null || method is! Procedure) {
      return;
    }
    if (klass != method.enclosingClass) {
      Supertype parent =
          hierarchy.getClassAsInstanceOf(klass, method.enclosingClass);
      klass = method.enclosingClass;
      receiverTypeArguments = parent.typeArguments;
    }
    Map<TypeParameter, DartType> substitutionMap = <TypeParameter, DartType>{};
    for (int i = 0; i < receiverTypeArguments.length; ++i) {
      substitutionMap[klass.typeParameters[i]] = receiverTypeArguments[i];
    }
    List<TypeParameter> methodParameters = method.function.typeParameters;
    // The error is to be reported elsewhere.
    if (methodParameters.length != arguments.types.length) return;
    List<TypeParameter> instantiatedMethodParameters =
        new List<TypeParameter>.filled(methodParameters.length, null);
    for (int i = 0; i < instantiatedMethodParameters.length; ++i) {
      instantiatedMethodParameters[i] =
          new TypeParameter(methodParameters[i].name);
      substitutionMap[methodParameters[i]] =
          new TypeParameterType.forAlphaRenaming(
              methodParameters[i], instantiatedMethodParameters[i]);
    }
    for (int i = 0; i < instantiatedMethodParameters.length; ++i) {
      instantiatedMethodParameters[i].bound =
          substitute(methodParameters[i].bound, substitutionMap);
    }

    final DartType bottomType = isNonNullableByDefault
        ? const NeverType.nonNullable()
        : const NullType();
    List<TypeArgumentIssue> issues = findTypeArgumentIssuesForInvocation(
        instantiatedMethodParameters,
        arguments.types,
        typeEnvironment,
        isNonNullableByDefault
            ? SubtypeCheckMode.withNullabilities
            : SubtypeCheckMode.ignoringNullabilities,
        bottomType,
        isNonNullableByDefault: library.isNonNullableByDefault,
        areGenericArgumentsAllowed: enableGenericMetadataInLibrary);
    reportTypeArgumentIssues(issues, fileUri, offset,
        typeArgumentsInfo: getTypeArgumentsInfo(arguments),
        targetReceiver: receiverType,
        targetName: name.text);
  }

  void checkBoundsInFunctionInvocation(
      TypeEnvironment typeEnvironment,
      ClassHierarchy hierarchy,
      TypeInferrerImpl typeInferrer,
      FunctionType functionType,
      String localName,
      Arguments arguments,
      Uri fileUri,
      int offset) {
    if (arguments.types.isEmpty) return;

    List<TypeParameter> functionTypeParameters = functionType.typeParameters;
    // The error is to be reported elsewhere.
    if (functionTypeParameters.length != arguments.types.length) return;
    final DartType bottomType = isNonNullableByDefault
        ? const NeverType.nonNullable()
        : const NullType();
    List<TypeArgumentIssue> issues = findTypeArgumentIssuesForInvocation(
        functionTypeParameters,
        arguments.types,
        typeEnvironment,
        isNonNullableByDefault
            ? SubtypeCheckMode.withNullabilities
            : SubtypeCheckMode.ignoringNullabilities,
        bottomType,
        isNonNullableByDefault: library.isNonNullableByDefault,
        areGenericArgumentsAllowed: enableGenericMetadataInLibrary);
    reportTypeArgumentIssues(issues, fileUri, offset,
        typeArgumentsInfo: getTypeArgumentsInfo(arguments),
        // TODO(johnniwinther): Special-case messaging on function type
        //  invocation to avoid reference to 'call' and use the function type
        //  instead.
        targetName: localName ?? 'call');
  }

  void checkTypesInOutline(TypeEnvironment typeEnvironment) {
    Iterator<Builder> iterator = this.iterator;
    while (iterator.moveNext()) {
      Builder declaration = iterator.current;
      if (declaration is FieldBuilder) {
        checkTypesInField(declaration, typeEnvironment);
      } else if (declaration is ProcedureBuilder) {
        checkTypesInProcedureBuilder(declaration, typeEnvironment);
        if (declaration.isGetter) {
          Builder setterDeclaration =
              scope.lookupLocalMember(declaration.name, setter: true);
          if (setterDeclaration != null) {
            checkGetterSetterTypes(
                declaration, setterDeclaration, typeEnvironment);
          }
        }
      } else if (declaration is SourceClassBuilder) {
        declaration.checkTypesInOutline(typeEnvironment);
      } else if (declaration is SourceExtensionBuilder) {
        declaration.checkTypesInOutline(typeEnvironment);
      } else if (declaration is SourceTypeAliasBuilder) {
        declaration.checkTypesInOutline(typeEnvironment);
      } else {
        assert(
            declaration is! TypeDeclarationBuilder ||
                declaration is BuiltinTypeDeclarationBuilder,
            "Unexpected declaration ${declaration.runtimeType}");
      }
    }
    inferredTypes.clear();
    checkUncheckedTypedefTypes(typeEnvironment);
  }

  void registerImplicitlyTypedField(FieldBuilder fieldBuilder) {
    (_implicitlyTypedFields ??= <FieldBuilder>[]).add(fieldBuilder);
  }

  @override
  List<FieldBuilder> takeImplicitlyTypedFields() {
    List<FieldBuilder> result = _implicitlyTypedFields;
    _implicitlyTypedFields = null;
    return result;
  }

  void forEachExtensionInScope(void Function(ExtensionBuilder) f) {
    if (_extensionsInScope == null) {
      _extensionsInScope = <ExtensionBuilder>{};
      scope.forEachExtension(_extensionsInScope.add);
      if (_prefixBuilders != null) {
        for (PrefixBuilder prefix in _prefixBuilders) {
          prefix.exportScope.forEachExtension(_extensionsInScope.add);
        }
      }
    }
    _extensionsInScope.forEach(f);
  }

  void clearExtensionsInScopeCache() {
    _extensionsInScope = null;
  }

  /// Set to some non-null name when entering a class; set to null when leaving
  /// the class.
  ///
  /// Called in OutlineBuilder.beginClassDeclaration,
  /// OutlineBuilder.endClassDeclaration,
  /// OutlineBuilder.beginMixinDeclaration,
  /// OutlineBuilder.endMixinDeclaration.
  void setCurrentClassName(String name) {
    if (name == null) {
      _currentClassReferencesFromIndexed = null;
    } else if (referencesFrom != null) {
      _currentClassReferencesFromIndexed =
          referencesFromIndexed.lookupIndexedClass(name);
    }
  }

  void registerPendingNullability(
      Uri fileUri, int charOffset, TypeParameterType type) {
    _pendingNullabilities
        .add(new PendingNullability(fileUri, charOffset, type));
  }

  /// Performs delayed bounds checks on [TypedefType]s for the library
  ///
  /// As [TypedefType]s are built, they are eagerly unaliased, making it
  /// impossible to perform the bounds checks on them at the time when the
  /// checks can be done. To perform the checks, [TypedefType]s are added to
  /// [uncheckedTypedefTypes] as they are built.  This method performs the
  /// checks and clears the list of the types for the delayed check.
  void checkUncheckedTypedefTypes(TypeEnvironment typeEnvironment) {
    for (UncheckedTypedefType uncheckedTypedefType in uncheckedTypedefTypes) {
      checkBoundsInType(uncheckedTypedefType.typeToCheck, typeEnvironment,
          uncheckedTypedefType.fileUri, uncheckedTypedefType.offset);
    }
    uncheckedTypedefTypes.clear();
  }
}

// The kind of type parameter scope built by a [TypeParameterScopeBuilder]
// object.
enum TypeParameterScopeKind {
  library,
  classOrNamedMixinApplication,
  classDeclaration,
  mixinDeclaration,
  unnamedMixinApplication,
  namedMixinApplication,
  extensionDeclaration,
  typedef,
  staticOrInstanceMethodOrConstructor,
  topLevelMethod,
  factoryMethod,
  functionType,
}

/// A builder object preparing for building declarations that can introduce type
/// parameter and/or members.
///
/// Unlike [Scope], this scope is used during construction of builders to
/// ensure types and members are added to and resolved in the correct location.
class TypeParameterScopeBuilder {
  TypeParameterScopeKind _kind;

  final TypeParameterScopeBuilder parent;

  final Map<String, Builder> members;

  final Map<String, Builder> constructors;

  final Map<String, MemberBuilder> setters;

  final Set<ExtensionBuilder> extensions;

  final List<UnresolvedType> types = <UnresolvedType>[];

  // TODO(johnniwinther): Stop using [_name] for determining the declaration
  // kind.
  String _name;

  /// Offset of name token, updated by the outline builder along
  /// with the name as the current declaration changes.
  int _charOffset;

  List<TypeVariableBuilder> _typeVariables;

  /// The type of `this` in instance methods declared in extension declarations.
  ///
  /// Instance methods declared in extension declarations methods are extended
  /// with a synthesized parameter of this type.
  TypeBuilder _extensionThisType;

  bool declaresConstConstructor = false;

  TypeParameterScopeBuilder(
      this._kind,
      this.members,
      this.setters,
      this.constructors,
      this.extensions,
      this._name,
      this._charOffset,
      this.parent) {
    assert(_name != null);
  }

  TypeParameterScopeBuilder.library()
      : this(
            TypeParameterScopeKind.library,
            <String, Builder>{},
            <String, MemberBuilder>{},
            null, // No support for constructors in library scopes.
            <ExtensionBuilder>{},
            "<library>",
            -1,
            null);

  TypeParameterScopeBuilder createNested(
      TypeParameterScopeKind kind, String name, bool hasMembers) {
    return new TypeParameterScopeBuilder(
        kind,
        hasMembers ? <String, MemberBuilder>{} : null,
        hasMembers ? <String, MemberBuilder>{} : null,
        hasMembers ? <String, MemberBuilder>{} : null,
        null, // No support for extensions in nested scopes.
        name,
        -1,
        this);
  }

  /// Registers that this builder is preparing for a class declaration with the
  /// given [name] and [typeVariables] located [charOffset].
  void markAsClassDeclaration(
      String name, int charOffset, List<TypeVariableBuilder> typeVariables) {
    assert(_kind == TypeParameterScopeKind.classOrNamedMixinApplication,
        "Unexpected declaration kind: $_kind");
    _kind = TypeParameterScopeKind.classDeclaration;
    _name = name;
    _charOffset = charOffset;
    _typeVariables = typeVariables;
  }

  /// Registers that this builder is preparing for a named mixin application
  /// with the given [name] and [typeVariables] located [charOffset].
  void markAsNamedMixinApplication(
      String name, int charOffset, List<TypeVariableBuilder> typeVariables) {
    assert(_kind == TypeParameterScopeKind.classOrNamedMixinApplication,
        "Unexpected declaration kind: $_kind");
    _kind = TypeParameterScopeKind.namedMixinApplication;
    _name = name;
    _charOffset = charOffset;
    _typeVariables = typeVariables;
  }

  /// Registers that this builder is preparing for a mixin declaration with the
  /// given [name] and [typeVariables] located [charOffset].
  void markAsMixinDeclaration(
      String name, int charOffset, List<TypeVariableBuilder> typeVariables) {
    // TODO(johnniwinther): Avoid using 'classOrNamedMixinApplication' for mixin
    // declaration. These are syntactically distinct so we don't need the
    // transition.
    assert(_kind == TypeParameterScopeKind.classOrNamedMixinApplication,
        "Unexpected declaration kind: $_kind");
    _kind = TypeParameterScopeKind.mixinDeclaration;
    _name = name;
    _charOffset = charOffset;
    _typeVariables = typeVariables;
  }

  /// Registers that this builder is preparing for an extension declaration with
  /// the given [name] and [typeVariables] located [charOffset].
  void markAsExtensionDeclaration(
      String name, int charOffset, List<TypeVariableBuilder> typeVariables) {
    assert(_kind == TypeParameterScopeKind.extensionDeclaration,
        "Unexpected declaration kind: $_kind");
    _name = name;
    _charOffset = charOffset;
    _typeVariables = typeVariables;
  }

  /// Registers the 'extension this type' of the extension declaration prepared
  /// for by this builder.
  ///
  /// See [extensionThisType] for terminology.
  void registerExtensionThisType(TypeBuilder type) {
    assert(_kind == TypeParameterScopeKind.extensionDeclaration,
        "DeclarationBuilder.registerExtensionThisType is not supported $_kind");
    assert(_extensionThisType == null,
        "Extension this type has already been set.");
    _extensionThisType = type;
  }

  /// Returns what kind of declaration this [TypeParameterScopeBuilder] is
  /// preparing for.
  ///
  /// This information is transient for some declarations. In particular
  /// classes and named mixin applications are initially created with the kind
  /// [TypeParameterScopeKind.classOrNamedMixinApplication] before a call to
  /// either [markAsClassDeclaration] or [markAsNamedMixinApplication] sets the
  /// value to its actual kind.
  // TODO(johnniwinther): Avoid the transition currently used on mixin
  // declarations.
  TypeParameterScopeKind get kind => _kind;

  String get name => _name;

  int get charOffset => _charOffset;

  List<TypeVariableBuilder> get typeVariables => _typeVariables;

  /// Returns the 'extension this type' of the extension declaration prepared
  /// for by this builder.
  ///
  /// The 'extension this type' is the type mentioned in the on-clause of the
  /// extension declaration. For instance `B` in this extension declaration:
  ///
  ///     extension A on B {
  ///       B method() => this;
  ///     }
  ///
  /// The 'extension this type' is the type if `this` expression in instance
  /// methods declared in extension declarations.
  TypeBuilder get extensionThisType {
    assert(kind == TypeParameterScopeKind.extensionDeclaration,
        "DeclarationBuilder.extensionThisType not supported on $kind.");
    assert(_extensionThisType != null,
        "DeclarationBuilder.extensionThisType has not been set on $this.");
    return _extensionThisType;
  }

  /// Adds the yet unresolved [type] to this scope builder.
  ///
  /// Unresolved type will be resolved through [resolveTypes] when the scope
  /// is fully built. This allows for resolving self-referencing types, like
  /// type parameter used in their own bound, for instance `<T extends A<T>>`.
  void addType(UnresolvedType type) {
    types.add(type);
  }

  /// Resolves type variables in [types] and propagate other types to [parent].
  void resolveTypes(
      List<TypeVariableBuilder> typeVariables, SourceLibraryBuilder library) {
    Map<String, TypeVariableBuilder> map;
    if (typeVariables != null) {
      map = <String, TypeVariableBuilder>{};
      for (TypeVariableBuilder builder in typeVariables) {
        map[builder.name] = builder;
      }
    }
    Scope scope;
    for (UnresolvedType type in types) {
      Object nameOrQualified = type.builder.name;
      String name = nameOrQualified is QualifiedName
          ? nameOrQualified.qualifier
          : nameOrQualified;
      Builder declaration;
      if (name != null) {
        if (members != null) {
          declaration = members[name];
        }
        if (declaration == null && map != null) {
          declaration = map[name];
        }
      }
      if (declaration == null) {
        // Since name didn't resolve in this scope, propagate it to the
        // parent declaration.
        parent.addType(type);
      } else if (nameOrQualified is QualifiedName) {
        NamedTypeBuilder builder = type.builder;
        // Attempt to use a member or type variable as a prefix.
        Message message = templateNotAPrefixInTypeAnnotation.withArguments(
            flattenName(
                nameOrQualified.qualifier, type.charOffset, type.fileUri),
            nameOrQualified.name);
        library.addProblem(message, type.charOffset,
            nameOrQualified.endCharOffset - type.charOffset, type.fileUri);
        builder.bind(builder.buildInvalidTypeDeclarationBuilder(
            message.withLocation(type.fileUri, type.charOffset,
                nameOrQualified.endCharOffset - type.charOffset)));
      } else {
        scope ??= toScope(null).withTypeVariables(typeVariables);
        type.resolveIn(scope, library);
      }
    }
    types.clear();
  }

  Scope toScope(Scope parent) {
    return new Scope(
        local: members,
        setters: setters,
        extensions: extensions,
        parent: parent,
        debugName: name,
        isModifiable: false);
  }

  @override
  String toString() => 'DeclarationBuilder(${hashCode}:kind=$kind,name=$name)';
}

class FieldInfo {
  final String name;
  final int charOffset;
  final Token initializerToken;
  final Token beforeLast;
  final int charEndOffset;

  const FieldInfo(this.name, this.charOffset, this.initializerToken,
      this.beforeLast, this.charEndOffset);
}

Uri computeLibraryUri(Builder declaration) {
  Builder current = declaration;
  do {
    if (current is LibraryBuilder) return current.importUri;
    current = current.parent;
  } while (current != null);
  return unhandled("no library parent", "${declaration.runtimeType}",
      declaration.charOffset, declaration.fileUri);
}

String extractName(name) => name is QualifiedName ? name.name : name;

class PostponedProblem {
  final Message message;
  final int charOffset;
  final int length;
  final Uri fileUri;

  PostponedProblem(this.message, this.charOffset, this.length, this.fileUri);
}

class LanguageVersion {
  final Version version;
  final Uri fileUri;
  final int charOffset;
  final int charCount;
  bool isFinal = false;

  LanguageVersion(this.version, this.fileUri, this.charOffset, this.charCount);

  bool get isExplicit => true;

  bool get valid => true;

  int get hashCode => version.hashCode * 13 + isExplicit.hashCode * 19;

  bool operator ==(Object other) {
    if (identical(this, other)) return true;
    return other is LanguageVersion &&
        version == other.version &&
        isExplicit == other.isExplicit;
  }

  String toString() {
    return 'LanguageVersion(version=$version,isExplicit=$isExplicit,'
        'fileUri=$fileUri,charOffset=$charOffset,charCount=$charCount)';
  }
}

class InvalidLanguageVersion implements LanguageVersion {
  final Uri fileUri;
  final int charOffset;
  final int charCount;
  final Version version;
  final bool isExplicit;
  bool isFinal = false;

  InvalidLanguageVersion(this.fileUri, this.charOffset, this.charCount,
      this.version, this.isExplicit);

  @override
  bool get valid => false;

  int get hashCode => isExplicit.hashCode * 19;

  bool operator ==(Object other) {
    if (identical(this, other)) return true;
    return other is InvalidLanguageVersion && isExplicit == other.isExplicit;
  }

  String toString() {
    return 'InvalidLanguageVersion(isExplicit=$isExplicit,'
        'fileUri=$fileUri,charOffset=$charOffset,charCount=$charCount)';
  }
}

class ImplicitLanguageVersion implements LanguageVersion {
  @override
  final Version version;
  bool isFinal = false;

  ImplicitLanguageVersion(this.version);

  @override
  bool get valid => true;

  @override
  Uri get fileUri => null;

  @override
  int get charOffset => -1;

  @override
  int get charCount => noLength;

  @override
  bool get isExplicit => false;

  bool operator ==(Object other) {
    if (identical(this, other)) return true;
    return other is ImplicitLanguageVersion && version == other.version;
  }

  @override
  String toString() {
    return 'ImplicitLanguageVersion(version=$version)';
  }
}

List<TypeVariableBuilder> _sortTypeVariablesTopologically(
    List<TypeVariableBuilder> typeVariables) {
  Set<TypeVariableBuilder> unhandled = new Set<TypeVariableBuilder>.identity()
    ..addAll(typeVariables);
  List<TypeVariableBuilder> result = <TypeVariableBuilder>[];
  while (unhandled.isNotEmpty) {
    TypeVariableBuilder rootVariable = unhandled.first;
    unhandled.remove(rootVariable);
    if (rootVariable.bound != null) {
      _sortTypeVariablesTopologicallyFromRoot(
          rootVariable.bound, unhandled, result);
    }
    result.add(rootVariable);
  }
  return result;
}

void _sortTypeVariablesTopologicallyFromRoot(TypeBuilder root,
    Set<TypeVariableBuilder> unhandled, List<TypeVariableBuilder> result) {
  assert(root != null);

  List<TypeVariableBuilder> typeVariables;
  List<TypeBuilder> internalDependents;

  if (root is NamedTypeBuilder) {
    TypeDeclarationBuilder declaration = root.declaration;
    if (declaration is ClassBuilder) {
      if (declaration.typeVariables != null &&
          declaration.typeVariables.isNotEmpty) {
        typeVariables = declaration.typeVariables;
      }
    } else if (declaration is TypeAliasBuilder) {
      if (declaration.typeVariables != null &&
          declaration.typeVariables.isNotEmpty) {
        typeVariables = declaration.typeVariables;
      }
      internalDependents = <TypeBuilder>[declaration.type];
    } else if (declaration is TypeVariableBuilder) {
      typeVariables = <TypeVariableBuilder>[declaration];
    }
  } else if (root is FunctionTypeBuilder) {
    if (root.typeVariables != null && root.typeVariables.isNotEmpty) {
      typeVariables = root.typeVariables;
    }
    if (root.formals != null && root.formals.isNotEmpty) {
      internalDependents = <TypeBuilder>[];
      for (FormalParameterBuilder formal in root.formals) {
        internalDependents.add(formal.type);
      }
    }
    if (root.returnType != null) {
      (internalDependents ??= <TypeBuilder>[]).add(root.returnType);
    }
  }

  if (typeVariables != null && typeVariables.isNotEmpty) {
    for (TypeVariableBuilder variable in typeVariables) {
      if (unhandled.contains(variable)) {
        unhandled.remove(variable);
        if (variable.bound != null) {
          _sortTypeVariablesTopologicallyFromRoot(
              variable.bound, unhandled, result);
        }
        result.add(variable);
      }
    }
  }
  if (internalDependents != null && internalDependents.isNotEmpty) {
    for (TypeBuilder type in internalDependents) {
      _sortTypeVariablesTopologicallyFromRoot(type, unhandled, result);
    }
  }
}

class PendingNullability {
  final Uri fileUri;
  final int charOffset;
  final TypeParameterType type;

  PendingNullability(this.fileUri, this.charOffset, this.type);
}

class UncheckedTypedefType {
  final TypedefType typeToCheck;

  // TODO(dmitryas): Make these fields nullable when the library is opted-in to
  // NNBD.
  int offset;
  Uri fileUri;

  UncheckedTypedefType(this.typeToCheck);
}