pkg/analyzer/lib/src/fine/library_manifest.dart

// Copyright (c) 2025, 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.

import 'dart:typed_data';

import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/src/dart/analysis/file_state.dart';
import 'package:analyzer/src/dart/element/element.dart';
import 'package:analyzer/src/fine/lookup_name.dart';
import 'package:analyzer/src/fine/manifest_context.dart';
import 'package:analyzer/src/fine/manifest_id.dart';
import 'package:analyzer/src/fine/manifest_item.dart';
import 'package:analyzer/src/summary2/data_reader.dart';
import 'package:analyzer/src/summary2/data_writer.dart';
import 'package:analyzer/src/summary2/linked_element_factory.dart';
import 'package:analyzer/src/util/performance/operation_performance.dart';
import 'package:analyzer/src/utilities/extensions/collection.dart';
import 'package:collection/collection.dart';

/// The manifest of a single library.
class LibraryManifest {
  /// The names that are re-exported by this library.
  /// This does not include names that are declared in this library.
  final Map<LookupName, ManifestItemId> reExportMap;

  final Map<LookupName, ClassItem> declaredClasses;
  final Map<LookupName, EnumItem> declaredEnums;
  final Map<LookupName, ExtensionItem> declaredExtensions;
  final Map<LookupName, ExtensionTypeItem> declaredExtensionTypes;
  final Map<LookupName, MixinItem> declaredMixins;
  final Map<LookupName, TypeAliasItem> declaredTypeAliases;
  final Map<LookupName, TopLevelGetterItem> declaredGetters;
  final Map<LookupName, TopLevelSetterItem> declaredSetters;
  final Map<LookupName, TopLevelFunctionItem> declaredFunctions;
  final Map<LookupName, TopLevelVariableItem> declaredVariables;

  LibraryManifest({
    required this.reExportMap,
    required this.declaredClasses,
    required this.declaredEnums,
    required this.declaredExtensions,
    required this.declaredExtensionTypes,
    required this.declaredMixins,
    required this.declaredTypeAliases,
    required this.declaredGetters,
    required this.declaredSetters,
    required this.declaredFunctions,
    required this.declaredVariables,
  });

  factory LibraryManifest.read(SummaryDataReader reader) {
    return LibraryManifest(
      reExportMap: reader.readLookupNameToIdMap(),
      declaredClasses: reader.readLookupNameMap(
        readValue: () => ClassItem.read(reader),
      ),
      declaredEnums: reader.readLookupNameMap(
        readValue: () => EnumItem.read(reader),
      ),
      declaredExtensions: reader.readLookupNameMap(
        readValue: () => ExtensionItem.read(reader),
      ),
      declaredExtensionTypes: reader.readLookupNameMap(
        readValue: () => ExtensionTypeItem.read(reader),
      ),
      declaredMixins: reader.readLookupNameMap(
        readValue: () => MixinItem.read(reader),
      ),
      declaredTypeAliases: reader.readLookupNameMap(
        readValue: () => TypeAliasItem.read(reader),
      ),
      declaredGetters: reader.readLookupNameMap(
        readValue: () => TopLevelGetterItem.read(reader),
      ),
      declaredSetters: reader.readLookupNameMap(
        readValue: () => TopLevelSetterItem.read(reader),
      ),
      declaredFunctions: reader.readLookupNameMap(
        readValue: () => TopLevelFunctionItem.read(reader),
      ),
      declaredVariables: reader.readLookupNameMap(
        readValue: () => TopLevelVariableItem.read(reader),
      ),
    );
  }

  Map<LookupName, ManifestItemId> get exportedIds {
    return Map.fromEntries([
      ...reExportMap.entries,
      ...<Map<LookupName, TopLevelItem>>[
            declaredClasses,
            declaredEnums,
            declaredExtensions,
            declaredExtensionTypes,
            declaredMixins,
            declaredTypeAliases,
            declaredGetters,
            declaredSetters,
            declaredFunctions,
          ]
          .expand((map) => map.entries)
          .whereNot((entry) => entry.key.isPrivate)
          .mapValue((item) => item.id),
    ]);
  }

  /// Returns the ID of a top-level element either declared or re-exported,
  /// or `null` if there is no such element.
  ManifestItemId? getExportedId(LookupName name) {
    return declaredClasses[name]?.id ??
        declaredEnums[name]?.id ??
        declaredExtensions[name]?.id ??
        declaredExtensionTypes[name]?.id ??
        declaredMixins[name]?.id ??
        declaredTypeAliases[name]?.id ??
        declaredGetters[name]?.id ??
        declaredSetters[name]?.id ??
        declaredFunctions[name]?.id ??
        reExportMap[name];
  }

  void write(BufferedSink sink) {
    reExportMap.write(sink);
    declaredClasses.write(sink);
    declaredEnums.write(sink);
    declaredExtensions.write(sink);
    declaredExtensionTypes.write(sink);
    declaredMixins.write(sink);
    declaredTypeAliases.write(sink);
    declaredGetters.write(sink);
    declaredSetters.write(sink);
    declaredFunctions.write(sink);
    declaredVariables.write(sink);
  }
}

class LibraryManifestBuilder {
  final LinkedElementFactory elementFactory;
  final List<LibraryFileKind> inputLibraries;
  late final List<LibraryElementImpl> libraryElements;

  /// The previous manifests for libraries.
  ///
  /// For correctness it does not matter what is in these manifests, they
  /// can be absent at all for any library (and they are for new libraries).
  /// But it does matter for performance, because we will give a new ID for any
  /// element that is not in the manifest, or have different "meaning". This
  /// will cause cascading changes to items that referenced these elements,
  /// new IDs for them, etc.
  final Map<Uri, LibraryManifest> inputManifests;

  /// Key: an element from [inputLibraries].
  /// Value: the item from [inputManifests], or newly build.
  ///
  /// We attempt to reuse the same item, most importantly its ID.
  ///
  /// It is filled initially during matching element structures.
  /// Then we remove those that affected by changed elements.
  ///
  /// Then we iterate over the elements in [libraryElements], and build new
  /// items for declared elements that don't have items in this map.
  final Map<Element, ManifestItem> declaredItems = Map.identity();

  /// The new manifests for libraries.
  final Map<Uri, LibraryManifest> newManifests = {};

  LibraryManifestBuilder({
    required this.elementFactory,
    required this.inputLibraries,
    required this.inputManifests,
  }) {
    libraryElements = inputLibraries
        .map((kind) {
          return elementFactory.libraryOfUri2(kind.file.uri);
        })
        .toList(growable: false);
  }

  Map<Uri, LibraryManifest> computeManifests({
    required OperationPerformanceImpl performance,
  }) {
    performance.getDataInt('libraryCount').add(inputLibraries.length);

    _fillItemMapFromInputManifests(performance: performance);

    _buildManifests();
    _addReExports();
    assert(_assertSerialization());

    return newManifests;
  }

  void _addClass({
    required EncodeContext encodingContext,
    required Map<LookupName, ClassItem> newItems,
    required ClassElementImpl2 element,
    required LookupName lookupName,
  }) {
    var classItem = _getOrBuildElementItem(element, () {
      return ClassItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });
    newItems[lookupName] = classItem;

    encodingContext.withTypeParameters(element.typeParameters2, (
      typeParameters,
    ) {
      classItem.beforeUpdatingMembers();
      _addInterfaceElementMembers(
        encodingContext: encodingContext,
        instanceElement: element,
        interfaceItem: classItem,
      );
    });
  }

  /// Class type aliases like `class B = A with M;` cannot explicitly declare
  /// any members. They have constructors, but these are based on the
  /// constructors of the supertype, and change if the supertype constructors
  /// change. So, it is enough to record that supertype constructors into
  /// the manifest.
  void _addClassTypeAliasConstructors() {
    var hasConstructors = <ClassElementImpl2>{};
    var inheritedMap = <ConstructorElementImpl2, ManifestItemId>{};

    void addForElement(ClassElementImpl2 element) {
      if (!element.isMixinApplication) {
        return;
      }

      // We might have already processed this element due to recursion.
      if (!hasConstructors.add(element)) {
        return;
      }

      // SAFETY: all items are already created.
      var item = declaredItems[element] as ClassItem;

      // SAFETY: we set `Object` during linking if it is not a class.
      var superElement = element.supertype!.element3;
      superElement as ClassElementImpl2;

      // The supertype could be a mixin application itself.
      addForElement(superElement);

      for (var constructor in element.constructors) {
        var lookupName = constructor.lookupName?.asLookupName;
        if (lookupName == null) {
          continue;
        }

        // SAFETY: we build inherited constructors from existing super.
        var superConstructor = constructor.superConstructor2!.baseElement;

        // Maybe the super constructor is "inherited" itself.
        var id = inheritedMap[superConstructor];

        // If not inherited, then must be declared.
        id ??= _getInterfaceElementMemberId(superConstructor);

        inheritedMap[constructor] = id;
        item.addInheritedConstructor(lookupName, id);
      }
    }

    for (var libraryElement in libraryElements) {
      for (var element in libraryElement.children2) {
        if (element is ClassElementImpl2) {
          addForElement(element);
        }
      }
    }
  }

  void _addEnum({
    required EncodeContext encodingContext,
    required Map<LookupName, TopLevelItem> newItems,
    required EnumElementImpl2 element,
    required LookupName lookupName,
  }) {
    var enumItem = _getOrBuildElementItem(element, () {
      return EnumItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });
    newItems[lookupName] = enumItem;

    encodingContext.withTypeParameters(element.typeParameters2, (
      typeParameters,
    ) {
      enumItem.beforeUpdatingMembers();
      _addInterfaceElementMembers(
        encodingContext: encodingContext,
        instanceElement: element,
        interfaceItem: enumItem,
      );
    });
  }

  void _addExtension({
    required EncodeContext encodingContext,
    required Map<LookupName, ExtensionItem> newItems,
    required ExtensionElementImpl2 element,
    required LookupName lookupName,
  }) {
    var extensionItem = _getOrBuildElementItem(element, () {
      return ExtensionItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });
    newItems[lookupName] = extensionItem;

    encodingContext.withTypeParameters(element.typeParameters2, (
      typeParameters,
    ) {
      extensionItem.beforeUpdatingMembers();
      _addInstanceElementMembers(
        encodingContext: encodingContext,
        instanceElement: element,
        instanceItem: extensionItem,
      );
    });
  }

  void _addExtensionType({
    required EncodeContext encodingContext,
    required Map<LookupName, TopLevelItem> newItems,
    required ExtensionTypeElementImpl2 element,
    required LookupName lookupName,
  }) {
    var extensionTypeItem = _getOrBuildElementItem(element, () {
      return ExtensionTypeItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });
    newItems[lookupName] = extensionTypeItem;

    encodingContext.withTypeParameters(element.typeParameters2, (
      typeParameters,
    ) {
      extensionTypeItem.beforeUpdatingMembers();
      _addInterfaceElementMembers(
        encodingContext: encodingContext,
        instanceElement: element,
        interfaceItem: extensionTypeItem,
      );
    });
  }

  void _addInstanceElementField({
    required EncodeContext encodingContext,
    required InstanceItem instanceItem,
    required FieldElementImpl2 element,
  }) {
    var lookupName = element.lookupName?.asLookupName;
    if (lookupName == null) {
      return;
    }

    var item = _getOrBuildElementItem(element, () {
      return InstanceItemFieldItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });

    instanceItem.declaredFields[lookupName] = item;
  }

  void _addInstanceElementGetter({
    required EncodeContext encodingContext,
    required InstanceItem instanceItem,
    required GetterElementImpl element,
  }) {
    var lookupName = element.lookupName?.asLookupName;
    if (lookupName == null) {
      return;
    }

    var item = _getOrBuildElementItem(element, () {
      return InstanceItemGetterItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });

    instanceItem.addDeclaredGetter(lookupName, item);
  }

  void _addInstanceElementMembers({
    required EncodeContext encodingContext,
    required InstanceElementImpl2 instanceElement,
    required InstanceItem instanceItem,
  }) {
    for (var field in instanceElement.fields) {
      _addInstanceElementField(
        encodingContext: encodingContext,
        instanceItem: instanceItem,
        element: field,
      );
    }

    for (var method in instanceElement.methods) {
      _addInstanceElementMethod(
        encodingContext: encodingContext,
        instanceItem: instanceItem,
        element: method,
      );
    }

    for (var getter in instanceElement.getters) {
      _addInstanceElementGetter(
        encodingContext: encodingContext,
        instanceItem: instanceItem,
        element: getter,
      );
    }

    for (var setter in instanceElement.setters) {
      _addInstanceElementSetter(
        encodingContext: encodingContext,
        instanceItem: instanceItem,
        element: setter,
      );
    }
  }

  void _addInstanceElementMethod({
    required EncodeContext encodingContext,
    required InstanceItem instanceItem,
    required MethodElementImpl2 element,
  }) {
    var lookupName = element.lookupName?.asLookupName;
    if (lookupName == null) {
      return;
    }

    var item = _getOrBuildElementItem(element, () {
      return InstanceItemMethodItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });

    instanceItem.addDeclaredMethod(lookupName, item);
  }

  void _addInstanceElementSetter({
    required EncodeContext encodingContext,
    required InstanceItem instanceItem,
    required SetterElementImpl element,
  }) {
    var lookupName = element.lookupName?.asLookupName;
    if (lookupName == null) {
      return;
    }

    var item = _getOrBuildElementItem(element, () {
      return InstanceItemSetterItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });

    instanceItem.addDeclaredSetter(lookupName, item);
  }

  void _addInterfaceElementConstructor({
    required EncodeContext encodingContext,
    required InterfaceItem interfaceItem,
    required ConstructorElementImpl2 element,
  }) {
    var lookupName = element.lookupName?.asLookupName;
    if (lookupName == null) {
      return;
    }

    var item = _getOrBuildElementItem(element, () {
      return InterfaceItemConstructorItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });

    interfaceItem.addDeclaredConstructor(lookupName, item);
  }

  void _addInterfaceElementMembers({
    required EncodeContext encodingContext,
    required InterfaceElementImpl2 instanceElement,
    required InterfaceItem interfaceItem,
  }) {
    // Class type aliases don't have declared members.
    // We don't consider constructors as declared.
    if (instanceElement is ClassElementImpl2 &&
        instanceElement.isMixinApplication) {
      return;
    }

    for (var constructor in instanceElement.constructors) {
      _addInterfaceElementConstructor(
        encodingContext: encodingContext,
        interfaceItem: interfaceItem,
        element: constructor,
      );
    }

    _addInstanceElementMembers(
      encodingContext: encodingContext,
      instanceElement: instanceElement,
      instanceItem: interfaceItem,
    );
  }

  void _addMixin({
    required EncodeContext encodingContext,
    required Map<LookupName, MixinItem> newItems,
    required MixinElementImpl2 element,
    required LookupName lookupName,
  }) {
    var mixinItem = _getOrBuildElementItem(element, () {
      return MixinItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });
    newItems[lookupName] = mixinItem;

    encodingContext.withTypeParameters(element.typeParameters2, (
      typeParameters,
    ) {
      mixinItem.beforeUpdatingMembers();
      _addInterfaceElementMembers(
        encodingContext: encodingContext,
        instanceElement: element,
        interfaceItem: mixinItem,
      );
    });
  }

  void _addReExports() {
    for (var libraryElement in libraryElements) {
      var libraryUri = libraryElement.uri;
      var manifest = newManifests[libraryUri]!;

      for (var entry in libraryElement.exportNamespace.definedNames2.entries) {
        var name = entry.key.asLookupName;
        var element = entry.value;

        // Skip elements that exist in nowhere.
        var elementLibraryUri = element.library2?.uri;
        if (elementLibraryUri == null) {
          continue;
        }

        // Skip elements declared in this library.
        if (elementLibraryUri == libraryUri) {
          continue;
        }

        // Skip if the element is declared in this library.
        if (element.library2 == libraryElement) {
          continue;
        }

        // Maybe exported from a library outside the current cycle.
        var id = elementFactory.getElementId(element);

        // If not, then look into new manifest.
        if (id == null) {
          var newManifest = newManifests[elementLibraryUri];
          id ??= newManifest?.getExportedId(name);
          // TODO(scheglov): repeat for re-re-exports
        }

        if (id == null) {
          // TODO(scheglov): complete
          continue;
        }
        manifest.reExportMap[name] = id;
      }
    }
  }

  void _addTopLevelFunction({
    required EncodeContext encodingContext,
    required Map<LookupName, TopLevelFunctionItem> newItems,
    required TopLevelFunctionElementImpl element,
    required LookupName lookupName,
  }) {
    var item = _getOrBuildElementItem(element, () {
      return TopLevelFunctionItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });
    newItems[lookupName] = item;
  }

  void _addTopLevelGetter({
    required EncodeContext encodingContext,
    required Map<LookupName, TopLevelGetterItem> newItems,
    required GetterElementImpl element,
    required LookupName lookupName,
  }) {
    var item = _getOrBuildElementItem(element, () {
      return TopLevelGetterItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });
    newItems[lookupName] = item;
  }

  void _addTopLevelSetter({
    required EncodeContext encodingContext,
    required Map<LookupName, TopLevelSetterItem> newItems,
    required SetterElementImpl element,
    required LookupName lookupName,
  }) {
    var item = _getOrBuildElementItem(element, () {
      return TopLevelSetterItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });
    newItems[lookupName] = item;
  }

  void _addTopLevelVariable({
    required EncodeContext encodingContext,
    required Map<LookupName, TopLevelVariableItem> newItems,
    required TopLevelVariableElementImpl2 element,
    required LookupName lookupName,
  }) {
    var item = _getOrBuildElementItem(element, () {
      return TopLevelVariableItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });
    newItems[lookupName] = item;
  }

  void _addTypeAlias({
    required EncodeContext encodingContext,
    required Map<LookupName, TypeAliasItem> newItems,
    required TypeAliasElementImpl2 element,
    required LookupName lookupName,
  }) {
    var item = _getOrBuildElementItem(element, () {
      return TypeAliasItem.fromElement(
        id: ManifestItemId.generate(),
        context: encodingContext,
        element: element,
      );
    });
    newItems[lookupName] = item;
  }

  /// Assert that every manifest can be serialized, and when deserialized
  /// results in the same manifest.
  bool _assertSerialization() {
    Uint8List manifestAsBytes(LibraryManifest manifest) {
      var byteSink = BufferedSink();
      manifest.write(byteSink);
      return byteSink.takeBytes();
    }

    newManifests.forEach((uri, manifest) {
      var bytes = manifestAsBytes(manifest);

      var readManifest = LibraryManifest.read(SummaryDataReader(bytes));
      var readBytes = manifestAsBytes(readManifest);

      if (!const ListEquality<int>().equals(bytes, readBytes)) {
        throw StateError('Library manifest bytes are different: $uri');
      }
    });

    return true;
  }

  /// Fill `result` with new library manifests.
  /// We reuse existing items when they fully match.
  /// We build new items for mismatched elements.
  Map<Uri, LibraryManifest> _buildManifests() {
    var encodingContext = EncodeContext(elementFactory: elementFactory);

    for (var libraryElement in libraryElements) {
      var libraryUri = libraryElement.uri;
      var newClassItems = <LookupName, ClassItem>{};
      var newEnumItems = <LookupName, EnumItem>{};
      var newExtensionItems = <LookupName, ExtensionItem>{};
      var newExtensionTypeItems = <LookupName, ExtensionTypeItem>{};
      var newMixinItems = <LookupName, MixinItem>{};
      var newTypeAliasItems = <LookupName, TypeAliasItem>{};
      var newTopLevelGetters = <LookupName, TopLevelGetterItem>{};
      var newTopLevelSetters = <LookupName, TopLevelSetterItem>{};
      var newTopLevelFunctions = <LookupName, TopLevelFunctionItem>{};
      var newTopLevelVariables = <LookupName, TopLevelVariableItem>{};

      for (var element in libraryElement.children2) {
        var lookupName = element.lookupName?.asLookupName;
        if (lookupName == null) {
          continue;
        }

        switch (element) {
          case ClassElementImpl2():
            _addClass(
              encodingContext: encodingContext,
              newItems: newClassItems,
              element: element,
              lookupName: lookupName,
            );
          case EnumElementImpl2():
            _addEnum(
              encodingContext: encodingContext,
              newItems: newEnumItems,
              element: element,
              lookupName: lookupName,
            );
          case ExtensionElementImpl2():
            _addExtension(
              encodingContext: encodingContext,
              newItems: newExtensionItems,
              element: element,
              lookupName: lookupName,
            );
          case ExtensionTypeElementImpl2():
            _addExtensionType(
              encodingContext: encodingContext,
              newItems: newExtensionTypeItems,
              element: element,
              lookupName: lookupName,
            );
          case GetterElementImpl():
            _addTopLevelGetter(
              encodingContext: encodingContext,
              newItems: newTopLevelGetters,
              element: element,
              lookupName: lookupName,
            );
          case MixinElementImpl2():
            _addMixin(
              encodingContext: encodingContext,
              newItems: newMixinItems,
              element: element,
              lookupName: lookupName,
            );
          case SetterElementImpl():
            _addTopLevelSetter(
              encodingContext: encodingContext,
              newItems: newTopLevelSetters,
              element: element,
              lookupName: lookupName,
            );
          case TopLevelFunctionElementImpl():
            _addTopLevelFunction(
              encodingContext: encodingContext,
              newItems: newTopLevelFunctions,
              element: element,
              lookupName: lookupName,
            );
          case TopLevelVariableElementImpl2():
            _addTopLevelVariable(
              encodingContext: encodingContext,
              newItems: newTopLevelVariables,
              element: element,
              lookupName: lookupName,
            );
          case TypeAliasElementImpl2():
            _addTypeAlias(
              encodingContext: encodingContext,
              newItems: newTypeAliasItems,
              element: element,
              lookupName: lookupName,
            );
        }
      }

      var newManifest = LibraryManifest(
        reExportMap: {},
        declaredClasses: newClassItems,
        declaredEnums: newEnumItems,
        declaredExtensions: newExtensionItems,
        declaredExtensionTypes: newExtensionTypeItems,
        declaredMixins: newMixinItems,
        declaredTypeAliases: newTypeAliasItems,
        declaredGetters: newTopLevelGetters,
        declaredSetters: newTopLevelSetters,
        declaredFunctions: newTopLevelFunctions,
        declaredVariables: newTopLevelVariables,
      );
      libraryElement.manifest = newManifest;
      newManifests[libraryUri] = newManifest;
    }

    _fillInterfaceElementsInterface();
    _addClassTypeAliasConstructors();

    return newManifests;
  }

  void _fillInterfaceElementInterface(InterfaceElementImpl2 element) {
    // We don't create items for elements without name.
    if (element.lookupName == null) {
      return;
    }

    // Must be created already.
    var item = declaredItems[element] as InterfaceItem;
    item.interface.beforeUpdating();

    var interface = element.inheritanceManager.getInterface2(element);
    for (var entry in interface.map2.entries) {
      var executable = entry.value.baseElement;

      var lookupName = executable.lookupName?.asLookupName;
      if (lookupName == null) {
        continue;
      }

      // We can see a private member only inside the library.
      // But we reanalyze the library when one of its files changes.
      if (lookupName.isPrivate) {
        continue;
      }

      var combinedCandidates = interface.combinedSignatures[entry.key];
      if (combinedCandidates != null) {
        var candidateElements =
            combinedCandidates
                .map((candidate) => candidate.baseElement)
                .toSet()
                .toList();
        if (candidateElements.length == 1) {
          executable = candidateElements[0];
        } else {
          var candidateIds =
              candidateElements.map((candidate) {
                return _getInterfaceElementMemberId(candidate);
              }).toList();
          var idList = ManifestItemIdList(candidateIds);
          var id = item.interface.combinedIdsTemp[idList];
          id ??= ManifestItemId.generate();
          item.interface.map[lookupName] = id;
          item.interface.combinedIds[idList] = id;
          continue;
        }
      }

      var id = _getInterfaceElementMemberId(executable);
      item.interface.map[lookupName] = id;
    }

    item.interface.afterUpdate();
  }

  void _fillInterfaceElementsInterface() {
    var librarySet = libraryElements.toSet();
    var interfaceSet = <InterfaceElementImpl2>{};

    void addInterfacesToFill(InterfaceElementImpl2 element) {
      // If not in this bundle, it has interface ready.
      if (!librarySet.contains(element.library2)) {
        return;
      }

      // Ensure that we have interfaces of supertypes first.
      for (var superType in element.allSupertypes) {
        addInterfacesToFill(superType.element3);
      }

      interfaceSet.add(element);
    }

    for (var libraryElement in libraryElements) {
      for (var element in libraryElement.children2) {
        if (element is InterfaceElementImpl2) {
          addInterfacesToFill(element);
        }
      }
    }

    // Fill interfaces of supertypes before interfaces of subtypes.
    // So that if there are synthetic top-merged members in interfaces of
    // supertypes (these members are not included into declared), we can
    // get corresponding IDs.
    for (var element in interfaceSet) {
      _fillInterfaceElementInterface(element);
    }
  }

  void _fillItemMapFromInputManifests({
    required OperationPerformanceImpl performance,
  }) {
    // Compare structures of the elements against the existing manifests.
    // At the end `affectedElements` is filled with mismatched by structure.
    // And for matched by structure we have reference maps.
    var refElementsMap = Map<Element, List<Element>>.identity();
    var refExternalIds = Map<Element, ManifestItemId>.identity();
    var affectedElements = Set<Element>.identity();
    for (var libraryElement in libraryElements) {
      var libraryUri = libraryElement.uri;
      var manifest = _getInputManifest(libraryUri);
      _LibraryMatch(
        manifest: manifest,
        library: libraryElement,
        itemMap: declaredItems,
        structureMismatched: affectedElements,
        refElementsMap: refElementsMap,
        refExternalIds: refExternalIds,
      ).compareStructures();
    }

    performance
      ..getDataInt('structureMatchedCount').add(declaredItems.length)
      ..getDataInt('structureMismatchedCount').add(affectedElements.length);

    // Propagate invalidation from referenced elements.
    // Both from external elements, and from input library elements.
    for (var element in refElementsMap.keys.toList()) {
      var refElements = refElementsMap[element];
      if (refElements != null) {
        for (var referencedElement in refElements) {
          // If the referenced element is from this bundle, and is determined
          // to be affected, this makes the current element affected.
          if (affectedElements.contains(referencedElement)) {
            // Move the element to affected.
            // Its dependencies are not interesting anymore.
            affectedElements.add(element);
            declaredItems.remove(element);
            refElementsMap.remove(element);
            break;
          }
          // Maybe has a different external id.
          var requiredExternalId = refExternalIds[referencedElement];
          if (requiredExternalId != null) {
            var currentId = elementFactory.getElementId(referencedElement);
            if (currentId != requiredExternalId) {
              // Move the element to affected.
              // Its dependencies are not interesting anymore.
              affectedElements.add(element);
              declaredItems.remove(element);
              refElementsMap.remove(element);
              break;
            }
          }
        }
      }
    }

    performance
      ..getDataInt('transitiveMatchedCount').add(declaredItems.length)
      ..getDataInt('transitiveAffectedCount').add(affectedElements.length);
  }

  /// Returns the manifest from [inputManifests], empty if absent.
  LibraryManifest _getInputManifest(Uri uri) {
    return inputManifests[uri] ??
        LibraryManifest(
          reExportMap: {},
          declaredClasses: {},
          declaredEnums: {},
          declaredExtensions: {},
          declaredExtensionTypes: {},
          declaredMixins: {},
          declaredTypeAliases: {},
          declaredGetters: {},
          declaredSetters: {},
          declaredFunctions: {},
          declaredVariables: {},
        );
  }

  ManifestItemId _getInterfaceElementMemberId(ExecutableElementImpl2 element) {
    var enclosingElement = element.enclosingElement;
    enclosingElement as InterfaceElementImpl2;

    var enclosingItem = declaredItems[enclosingElement];
    if (enclosingItem != null) {
      // SAFETY: if item is in this library, it is for interface.
      enclosingItem as InterfaceItem;

      // SAFETY: any element in interface has a name.
      var lookupName = element.lookupName!.asLookupName;

      // Check for a conflict.
      if (enclosingItem.declaredConflicts[lookupName] case var id?) {
        return id;
      }

      // SAFETY: null asserts are safe, because element is in this library.
      switch (element) {
        case GetterElementImpl():
          var declaredGetter = enclosingItem.declaredGetters[lookupName];
          if (declaredGetter != null) {
            return declaredGetter.id;
          }
          return enclosingItem.interface.map[lookupName]!;
        case SetterElementImpl():
          var declaredSetter = enclosingItem.declaredSetters[lookupName];
          if (declaredSetter != null) {
            return declaredSetter.id;
          }
          return enclosingItem.interface.map[lookupName]!;
        case MethodElementImpl2():
          var declaredMethod = enclosingItem.declaredMethods[lookupName];
          if (declaredMethod != null) {
            return declaredMethod.id;
          }
          return enclosingItem.interface.map[lookupName]!;
        case ConstructorElementImpl2():
          if (enclosingItem.declaredConstructors[lookupName] case var item?) {
            return item.id;
          }
          return enclosingItem.inheritedConstructors[lookupName]!;
      }
    }

    return elementFactory.getElementId(element)!;
  }

  /// Returns either the existing item from [declaredItems], or builds a new one.
  Item _getOrBuildElementItem<
    E extends ElementImpl2,
    Item extends ManifestItem
  >(E element, Item Function() build) {
    // We assume that when matching elements against the structure of
    // the item, we put into [itemMap] only the type of the item that
    // corresponds the type of the element.
    var item = declaredItems[element] as Item?;
    if (item == null) {
      item = build();
      // To find IDs of inherited members.
      declaredItems[element] = item;
    }
    return item;
  }
}

/// Compares structures of [library] children against [manifest].
class _LibraryMatch {
  final LibraryElementImpl library;

  /// A previous manifest for the [library].
  ///
  /// Strictly speaking, it does not have to be the latest manifest, it could
  /// be empty at all (and is empty when this is a new library). It is used
  /// to give the same identifiers to the elements with the same meaning.
  final LibraryManifest manifest;

  /// Elements that have structure matching the corresponding items from
  /// [manifest].
  final Map<Element, ManifestItem> itemMap;

  /// Elements with mismatched structure.
  /// These elements will get new identifiers.
  final Set<Element> structureMismatched;

  /// Key: an element of [library].
  /// Value: the elements that the key references.
  ///
  /// This includes references to elements of this bundle, and of external
  /// bundles. This information allows propagating invalidation from affected
  /// elements to their dependents.
  // TODO(scheglov): hm... maybe store it? And reverse it.
  final Map<Element, List<Element>> refElementsMap;

  /// Key: an element from an external bundle.
  /// Value: the identifier at the time when [manifest] was built.
  ///
  /// If [LibraryManifestBuilder] later finds that some of these elements now
  /// have different identifiers, it propagates invalidation using
  /// [refElementsMap].
  final Map<Element, ManifestItemId> refExternalIds;

  _LibraryMatch({
    required this.manifest,
    required this.library,
    required this.itemMap,
    required this.refElementsMap,
    required this.refExternalIds,
    required this.structureMismatched,
  });

  void compareStructures() {
    for (var element in library.children2) {
      var name = element.lookupName?.asLookupName;
      switch (element) {
        case ClassElementImpl2():
          if (!_matchClass(name: name, element: element)) {
            structureMismatched.add(element);
          }
        case EnumElementImpl2():
          if (!_matchEnum(name: name, element: element)) {
            structureMismatched.add(element);
          }
        case ExtensionElementImpl2():
          if (!_matchExtension(name: name, element: element)) {
            structureMismatched.add(element);
          }
        case ExtensionTypeElementImpl2():
          if (!_matchExtensionType(name: name, element: element)) {
            structureMismatched.add(element);
          }
        case GetterElementImpl():
          if (!_matchTopGetter(name: name, element: element)) {
            structureMismatched.add(element);
          }
        case MixinElementImpl2():
          if (!_matchMixin(name: name, element: element)) {
            structureMismatched.add(element);
          }
        case SetterElementImpl():
          if (!_matchTopSetter(name: name, element: element)) {
            structureMismatched.add(element);
          }
        case TopLevelFunctionElementImpl():
          if (!_matchTopFunction(name: name, element: element)) {
            structureMismatched.add(element);
          }
        case TopLevelVariableElementImpl2():
          if (!_matchTopVariable(name: name, element: element)) {
            structureMismatched.add(element);
          }
        case TypeAliasElementImpl2():
          if (!_matchTypeAlias(name: name, element: element)) {
            structureMismatched.add(element);
          }
      }
    }
  }

  /// Records [item] as matching [element], and stores dependencies.
  ///
  /// The fact that it does match is checked outside.
  void _addMatchingElementItem(
    ElementImpl2 element,
    ManifestItem item,
    MatchContext matchContext,
  ) {
    itemMap[element] = item;
    refElementsMap[element] = matchContext.elementList;
    refExternalIds.addAll(matchContext.externalIds);
  }

  bool _matchClass({
    required LookupName? name,
    required ClassElementImpl2 element,
  }) {
    var item = manifest.declaredClasses[name];
    if (item == null) {
      return false;
    }

    var matchContext = MatchContext(parent: null);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);

    _matchInterfaceElementConstructors(
      interfaceElement: element,
      item: item,
      matchContext: matchContext,
    );

    _matchInstanceElementExecutables(
      element: element,
      item: item,
      matchContext: matchContext,
    );

    return true;
  }

  bool _matchEnum({
    required LookupName? name,
    required EnumElementImpl2 element,
  }) {
    var item = manifest.declaredEnums[name];
    if (item is! EnumItem) {
      return false;
    }

    var matchContext = MatchContext(parent: null);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);

    _matchInterfaceElementConstructors(
      matchContext: matchContext,
      interfaceElement: element,
      item: item,
    );

    _matchInstanceElementExecutables(
      matchContext: matchContext,
      element: element,
      item: item,
    );

    return true;
  }

  bool _matchExtension({
    required LookupName? name,
    required ExtensionElementImpl2 element,
  }) {
    var item = manifest.declaredExtensions[name];
    if (item == null) {
      return false;
    }

    var matchContext = MatchContext(parent: null);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);

    _matchInstanceElementExecutables(
      matchContext: matchContext,
      element: element,
      item: item,
    );

    return true;
  }

  bool _matchExtensionType({
    required LookupName? name,
    required ExtensionTypeElementImpl2 element,
  }) {
    var item = manifest.declaredExtensionTypes[name];
    if (item is! ExtensionTypeItem) {
      return false;
    }

    var matchContext = MatchContext(parent: null);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);

    _matchInterfaceElementConstructors(
      matchContext: matchContext,
      interfaceElement: element,
      item: item,
    );

    _matchInstanceElementExecutables(
      matchContext: matchContext,
      element: element,
      item: item,
    );

    return true;
  }

  void _matchInstanceElementExecutables({
    required InstanceElementImpl2 element,
    required InstanceItem item,
    required MatchContext matchContext,
  }) {
    for (var field in element.fields) {
      if (!_matchInstanceElementField(
        instanceItem: item,
        instanceMatchContext: matchContext,
        element: field,
      )) {
        structureMismatched.add(field);
      }
    }

    for (var method in element.methods) {
      if (!_matchInstanceElementMethod(
        instanceItem: item,
        instanceMatchContext: matchContext,
        element: method,
      )) {
        structureMismatched.add(method);
      }
    }

    for (var getter in element.getters) {
      if (!_matchInstanceElementGetter(
        instanceItem: item,
        instanceMatchContext: matchContext,
        element: getter,
      )) {
        structureMismatched.add(getter);
      }
    }

    for (var setter in element.setters) {
      if (!_matchInstanceElementSetter(
        instanceItem: item,
        instanceMatchContext: matchContext,
        element: setter,
      )) {
        structureMismatched.add(setter);
      }
    }
  }

  bool _matchInstanceElementField({
    required InstanceItem instanceItem,
    required MatchContext instanceMatchContext,
    required FieldElementImpl2 element,
  }) {
    var lookupName = element.lookupName?.asLookupName;
    if (lookupName == null) {
      return true;
    }

    var item = instanceItem.declaredFields[lookupName];
    if (item == null) {
      return false;
    }

    var matchContext = MatchContext(parent: instanceMatchContext);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);
    return true;
  }

  bool _matchInstanceElementGetter({
    required InstanceItem instanceItem,
    required MatchContext instanceMatchContext,
    required GetterElementImpl element,
  }) {
    var lookupName = element.lookupName?.asLookupName;
    if (lookupName == null) {
      return false;
    }

    var item = instanceItem.declaredGetters[lookupName];
    if (item is! InstanceItemGetterItem) {
      return false;
    }

    var matchContext = MatchContext(parent: instanceMatchContext);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);
    return true;
  }

  bool _matchInstanceElementMethod({
    required InstanceItem instanceItem,
    required MatchContext instanceMatchContext,
    required MethodElementImpl2 element,
  }) {
    var lookupName = element.lookupName?.asLookupName;
    if (lookupName == null) {
      return false;
    }

    var item = instanceItem.declaredMethods[lookupName];
    if (item is! InstanceItemMethodItem) {
      return false;
    }

    var matchContext = MatchContext(parent: instanceMatchContext);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);
    return true;
  }

  bool _matchInstanceElementSetter({
    required InstanceItem instanceItem,
    required MatchContext instanceMatchContext,
    required SetterElementImpl element,
  }) {
    var lookupName = element.lookupName?.asLookupName;
    if (lookupName == null) {
      return true;
    }

    var item = instanceItem.declaredSetters[lookupName];
    if (item is! InstanceItemSetterItem) {
      return false;
    }

    var matchContext = MatchContext(parent: instanceMatchContext);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);
    return true;
  }

  bool _matchInterfaceElementConstructor({
    required InterfaceItem interfaceItem,
    required MatchContext interfaceMatchContext,
    required ConstructorElementImpl2 element,
  }) {
    var lookupName = element.lookupName?.asLookupName;
    if (lookupName == null) {
      return false;
    }

    var item = interfaceItem.declaredConstructors[lookupName];
    if (item is! InterfaceItemConstructorItem) {
      return false;
    }

    var matchContext = MatchContext(parent: interfaceMatchContext);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);
    return true;
  }

  void _matchInterfaceElementConstructors({
    required MatchContext matchContext,
    required InterfaceElementImpl2 interfaceElement,
    required InterfaceItem item,
  }) {
    for (var constructor in interfaceElement.constructors) {
      if (!_matchInterfaceElementConstructor(
        interfaceItem: item,
        interfaceMatchContext: matchContext,
        element: constructor,
      )) {
        structureMismatched.add(constructor);
      }
    }
  }

  bool _matchMixin({
    required LookupName? name,
    required MixinElementImpl2 element,
  }) {
    var item = manifest.declaredMixins[name];
    if (item == null) {
      return false;
    }

    var matchContext = MatchContext(parent: null);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);

    _matchInstanceElementExecutables(
      element: element,
      item: item,
      matchContext: matchContext,
    );

    return true;
  }

  bool _matchTopFunction({
    required LookupName? name,
    required TopLevelFunctionElementImpl element,
  }) {
    var item = manifest.declaredFunctions[name];
    if (item == null) {
      return false;
    }

    var matchContext = MatchContext(parent: null);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);
    return true;
  }

  bool _matchTopGetter({
    required LookupName? name,
    required GetterElementImpl element,
  }) {
    var item = manifest.declaredGetters[name];
    if (item == null) {
      return false;
    }

    var matchContext = MatchContext(parent: null);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);
    return true;
  }

  bool _matchTopSetter({
    required LookupName? name,
    required SetterElementImpl element,
  }) {
    var item = manifest.declaredSetters[name];
    if (item == null) {
      return false;
    }

    var matchContext = MatchContext(parent: null);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);
    return true;
  }

  bool _matchTopVariable({
    required LookupName? name,
    required TopLevelVariableElementImpl2 element,
  }) {
    var item = manifest.declaredVariables[name];
    if (item == null) {
      return false;
    }

    var matchContext = MatchContext(parent: null);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);
    return true;
  }

  bool _matchTypeAlias({
    required LookupName? name,
    required TypeAliasElementImpl2 element,
  }) {
    var item = manifest.declaredTypeAliases[name];
    if (item == null) {
      return false;
    }

    var matchContext = MatchContext(parent: null);
    if (!item.match(matchContext, element)) {
      return false;
    }

    _addMatchingElementItem(element, item, matchContext);

    return true;
  }
}