pkg/analyzer/lib/src/summary/link.dart

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

/**
 * This library is capable of producing linked summaries from unlinked
 * ones (or prelinked ones).  It functions by building a miniature
 * element model to represent the contents of the summaries, and then
 * scanning the element model to gather linked information and adding
 * it to the summary data structures.
 *
 * The reason we use a miniature element model to do the linking
 * (rather than resynthesizing the full element model from the
 * summaries) is that it is expected that we will only need to
 * traverse a small subset of the element properties in order to link.
 * Resynthesizing only those properties that we need should save
 * substantial CPU time.
 *
 * The element model implements the same interfaces as the full
 * element model, so we can re-use code elsewhere in the analysis
 * engine to do the linking.  However, only a small subset of the
 * methods and getters defined in the full element model are
 * implemented here.  To avoid static warnings, each element model
 * class contains an implementation of `noSuchMethod`.
 *
 * The miniature element model follows the following design
 * principles:
 *
 * - With few exceptions, resynthesis is done incrementally on demand,
 *   so that we don't pay the cost of resynthesizing elements (or
 *   properties of elements) that aren't referenced from a part of the
 *   element model that is relevant to linking.
 *
 * - Computation of values in the miniature element model is similar
 *   to the task model, but much lighter weight.  Instead of declaring
 *   tasks and their relationships using classes, each task is simply
 *   a method (frequently a getter) that computes a value.  Instead of
 *   using a general purpose cache, values are cached by the methods
 *   themselves in private fields (with `null` typically representing
 *   "not yet cached").
 *
 * - No attempt is made to detect cyclic dependencies due to bugs in
 *   the analyzer.  This saves time because dependency evaluation
 *   doesn't have to be a separate step from evaluating a value; we
 *   can simply call the getter.
 *
 * - However, for cases where cyclic dependencies may occur in the
 *   absence of analyzer bugs (e.g. because of errors in the code
 *   being analyzed, or cycles between top level and static variables
 *   undergoing type inference), we do precompute dependencies, and we
 *   use Tarjan's strongly connected components algorithm to detect
 *   cycles.
 *
 * - As much as possible, bookkeeping data is pointed to directly by
 *   the element objects, rather than being stored in maps.
 *
 * - Where possible, we favor method dispatch instead of "is" and "as"
 *   checks.  E.g. see [ReferenceableElementForLink.asConstructor].
 */
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/ast/token.dart' show TokenType;
import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/dart/element/type.dart';
import 'package:analyzer/src/dart/constant/value.dart';
import 'package:analyzer/src/dart/element/element.dart';
import 'package:analyzer/src/dart/element/type.dart';
import 'package:analyzer/src/dart/resolver/inheritance_manager.dart';
import 'package:analyzer/src/generated/engine.dart';
import 'package:analyzer/src/generated/resolver.dart';
import 'package:analyzer/src/generated/static_type_analyzer.dart';
import 'package:analyzer/src/generated/utilities_dart.dart';
import 'package:analyzer/src/summary/format.dart';
import 'package:analyzer/src/summary/idl.dart';
import 'package:analyzer/src/summary/prelink.dart';
import 'package:analyzer/src/task/strong_mode.dart';
import 'package:front_end/src/dependency_walker.dart';

bool isIncrementOrDecrement(UnlinkedExprAssignOperator operator) {
  switch (operator) {
    case UnlinkedExprAssignOperator.prefixDecrement:
    case UnlinkedExprAssignOperator.prefixIncrement:
    case UnlinkedExprAssignOperator.postfixDecrement:
    case UnlinkedExprAssignOperator.postfixIncrement:
      return true;
    default:
      return false;
  }
}

/**
 * Link together the build unit consisting of [libraryUris], using
 * [getDependency] to fetch the [LinkedLibrary] objects from other
 * build units, and [getUnit] to fetch the [UnlinkedUnit] objects from
 * both this build unit and other build units.
 *
 * The [strong] flag controls whether type inference is performed in strong
 * mode or spec mode.  Note that in spec mode, the only types that are inferred
 * are the types of initializing formals, which are inferred from the types of
 * the corresponding fields.
 *
 * A map is returned whose keys are the URIs of the libraries in this
 * build unit, and whose values are the corresponding
 * [LinkedLibraryBuilder]s.
 */
Map<String, LinkedLibraryBuilder> link(
    Set<String> libraryUris,
    GetDependencyCallback getDependency,
    GetUnitCallback getUnit,
    GetDeclaredVariable getDeclaredVariable,
    bool strong) {
  Map<String, LinkedLibraryBuilder> linkedLibraries =
      setupForLink(libraryUris, getUnit, getDeclaredVariable);
  relink(linkedLibraries, getDependency, getUnit, strong);
  return linkedLibraries;
}

/**
 * Given [libraries] (a map from URI to [LinkedLibraryBuilder]
 * containing correct prelinked information), rebuild linked
 * information, using [getDependency] to fetch the [LinkedLibrary]
 * objects from other build units, and [getUnit] to fetch the
 * [UnlinkedUnit] objects from both this build unit and other build
 * units.
 *
 * The [strong] flag controls whether type inference is performed in strong
 * mode or spec mode.  Note that in spec mode, the only types that are inferred
 * are the types of initializing formals, which are inferred from the types of
 * the corresponding fields.
 */
void relink(Map<String, LinkedLibraryBuilder> libraries,
    GetDependencyCallback getDependency, GetUnitCallback getUnit, bool strong) {
  new Linker(libraries, getDependency, getUnit, strong).link();
}

/**
 * Prepare to link together the build unit consisting of [libraryUris], using
 * [getUnit] to fetch the [UnlinkedUnit] objects from both this build unit and
 * other build units.
 *
 * The libraries are prelinked, and a map is returned whose keys are the URIs of
 * the libraries in this build unit, and whose values are the corresponding
 * [LinkedLibraryBuilder]s.
 */
Map<String, LinkedLibraryBuilder> setupForLink(Set<String> libraryUris,
    GetUnitCallback getUnit, GetDeclaredVariable getDeclaredVariable) {
  Map<String, LinkedLibraryBuilder> linkedLibraries =
      <String, LinkedLibraryBuilder>{};
  for (String absoluteUri in libraryUris) {
    linkedLibraries[absoluteUri] = prelink(
        absoluteUri,
        getUnit(absoluteUri),
        getUnit,
        (String absoluteUri) => getUnit(absoluteUri)?.publicNamespace,
        getDeclaredVariable);
  }
  return linkedLibraries;
}

/**
 * Create an [EntityRefBuilder] representing the given [type], in a form
 * suitable for inclusion in [LinkedUnit.types].  [compilationUnit] is the
 * compilation unit in which the type will be used.  If [slot] is provided, it
 * is stored in [EntityRefBuilder.slot].
 */
EntityRefBuilder _createLinkedType(
    DartType type,
    CompilationUnitElementInBuildUnit compilationUnit,
    TypeParameterizedElementMixin typeParameterContext,
    {int slot}) {
  EntityRefBuilder result = new EntityRefBuilder(slot: slot);
  if (type is InterfaceType) {
    ClassElementForLink element = type.element;
    result.reference = compilationUnit.addReference(element);
    _storeTypeArguments(
        type.typeArguments, result, compilationUnit, typeParameterContext);
    return result;
  } else if (type is DynamicTypeImpl) {
    result.reference = compilationUnit.addRawReference('dynamic');
    return result;
  } else if (type is VoidTypeImpl) {
    result.reference = compilationUnit.addRawReference('void');
    return result;
  } else if (type is BottomTypeImpl) {
    result.reference = compilationUnit.addRawReference('*bottom*');
    return result;
  } else if (type is TypeParameterType) {
    TypeParameterElementImpl element = type.element;
    if (typeParameterContext.isTypeParameterInScope(element)) {
      result.paramReference =
          typeParameterContext.typeParameterNestingLevel - element.nestingLevel;
    } else {
      throw new StateError('The type parameter $type (in ${element?.location}) '
          'is out of scope on ${typeParameterContext?.location}.');
    }
    return result;
  } else if (type is FunctionType) {
    Element element = type.element;
    if (element is FunctionElementForLink_FunctionTypedParam) {
      result.reference =
          compilationUnit.addReference(element.typeParameterContext);
      result.implicitFunctionTypeIndices = element.implicitFunctionTypeIndices;
      _storeTypeArguments(
          type.typeArguments, result, compilationUnit, typeParameterContext);
      return result;
    }
    if (element is TopLevelFunctionElementForLink) {
      result.reference = compilationUnit.addReference(element);
      _storeTypeArguments(
          type.typeArguments, result, compilationUnit, typeParameterContext);
      return result;
    }
    if (element is MethodElementForLink) {
      result.reference = compilationUnit.addReference(element);
      _storeTypeArguments(
          type.typeArguments, result, compilationUnit, typeParameterContext);
      return result;
    }
    if (element is FunctionTypeAliasElementForLink) {
      result.reference = compilationUnit.addReference(element);
      _storeTypeArguments(
          type.typeArguments, result, compilationUnit, typeParameterContext);
      return result;
    }
    if (element is FunctionElement && element.enclosingElement == null) {
      // Element is a synthetic function element that was generated on the fly
      // to represent a type that has no associated source code location.
      result.syntheticReturnType = _createLinkedType(
          element.returnType, compilationUnit, typeParameterContext);
      result.entityKind =
          element.returnType?.element is GenericFunctionTypeElement
              ? EntityRefKind.genericFunctionType
              : EntityRefKind.syntheticFunction;
      result.syntheticParams = element.parameters
          .map((ParameterElement param) => _serializeSyntheticParam(
              param, compilationUnit, typeParameterContext))
          .toList();
      return result;
    }
    if (element is FunctionElement) {
      // Element is a local function inside another executable.
      result.reference = compilationUnit.addReference(element);
      // TODO(paulberry): do I need to store type arguments?
      return result;
    }
    // TODO(paulberry): implement other cases.
    throw new UnimplementedError('${element.runtimeType}');
  }
  // TODO(paulberry): implement other cases.
  throw new UnimplementedError('${type.runtimeType}');
}

DartType _dynamicIfNull(DartType type) {
  if (type == null || type.isBottom || type.isDartCoreNull) {
    return DynamicTypeImpl.instance;
  }
  return type;
}

/**
 * Create an [UnlinkedParam] representing the given [parameter], which should be
 * a parameter of a synthetic function type (e.g. one produced during type
 * inference as a result of computing the least upper bound of two function
 * types).
 */
UnlinkedParamBuilder _serializeSyntheticParam(
    ParameterElement parameter,
    CompilationUnitElementInBuildUnit compilationUnit,
    TypeParameterizedElementMixin typeParameterContext) {
  UnlinkedParamBuilder b = new UnlinkedParamBuilder();
  b.name = parameter.name;
  switch (parameter.parameterKind) {
    case ParameterKind.REQUIRED:
      b.kind = UnlinkedParamKind.required;
      break;
    case ParameterKind.POSITIONAL:
      b.kind = UnlinkedParamKind.positional;
      break;
    case ParameterKind.NAMED:
      b.kind = UnlinkedParamKind.named;
      break;
  }
  DartType type = parameter.type;
  if (!parameter.hasImplicitType) {
    if (type is FunctionType && type.element.isSynthetic) {
      b.isFunctionTyped = true;
      b.type = _createLinkedType(
          type.returnType, compilationUnit, typeParameterContext);
      b.parameters = type.parameters
          .map((parameter) => _serializeSyntheticParam(
              parameter, compilationUnit, typeParameterContext))
          .toList();
    } else {
      b.type = _createLinkedType(type, compilationUnit, typeParameterContext);
    }
  }
  return b;
}

/**
 * Store the given [typeArguments] in [encodedType], using [compilationUnit] and
 * [typeParameterContext] to serialize them.
 */
void _storeTypeArguments(
    List<DartType> typeArguments,
    EntityRefBuilder encodedType,
    CompilationUnitElementInBuildUnit compilationUnit,
    TypeParameterizedElementMixin typeParameterContext) {
  int count = typeArguments.length;
  List<EntityRefBuilder> encodedTypeArguments =
      new List<EntityRefBuilder>(count);
  for (int i = 0; i < count; i++) {
    encodedTypeArguments[i] = _createLinkedType(
        typeArguments[i], compilationUnit, typeParameterContext);
  }
  encodedType.typeArguments = encodedTypeArguments;
}

/**
 * Type of the callback used by [link] and [relink] to request
 * [LinkedLibrary] objects from other build units.
 */
typedef LinkedLibrary GetDependencyCallback(String absoluteUri);

/**
 * Type of the callback used by [link] and [relink] to request
 * [UnlinkedUnit] objects.
 */
typedef UnlinkedUnit GetUnitCallback(String absoluteUri);

/**
 * Stub implementation of [AnalysisOptions] used during linking.
 */
class AnalysisOptionsForLink implements AnalysisOptions {
  final Linker _linker;

  AnalysisOptionsForLink(this._linker);

  @override
  bool get strongMode => _linker.strongMode;

  @override
  noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
}

/**
 * Element representing a class or enum resynthesized from a summary
 * during linking.
 */
abstract class ClassElementForLink extends Object
    with ReferenceableElementForLink
    implements AbstractClassElementImpl {
  Map<String, ReferenceableElementForLink> _containedNames;

  @override
  final CompilationUnitElementForLink enclosingElement;

  /// TODO(brianwilkerson) This appears to be unused and might be removable.
  bool hasBeenInferred;

  ClassElementForLink(CompilationUnitElementForLink enclosingElement)
      : enclosingElement = enclosingElement,
        hasBeenInferred = !enclosingElement.isInBuildUnit;

  @override
  List<PropertyAccessorElementForLink> get accessors;

  @override
  ClassElementForLink get asClass => this;

  @override
  ConstructorElementForLink get asConstructor => unnamedConstructor;

  @override
  DartType get asStaticType =>
      enclosingElement.enclosingElement._linker.typeProvider.typeType;

  @override
  List<ConstructorElementForLink> get constructors;

  @override
  CompilationUnitElementImpl get enclosingUnit => enclosingElement;

  @override
  List<FieldElementForLink> get fields;

  /**
   * Indicates whether this is the core class `Object`.
   */
  bool get isObject;

  @override
  LibraryElementForLink get library => enclosingElement.library;

  @override
  List<MethodElementForLink> get methods;

  @override
  String get name;

  @override
  ConstructorElementForLink get unnamedConstructor;

  @override
  ReferenceableElementForLink getContainedName(String name) {
    if (_containedNames == null) {
      _containedNames = <String, ReferenceableElementForLink>{};
      // TODO(paulberry): what's the correct way to handle name conflicts?
      for (ConstructorElementForLink constructor in constructors) {
        _containedNames[constructor.name] = constructor;
      }
      for (PropertyAccessorElementForLink accessor in accessors) {
        _containedNames[accessor.name] = accessor;
      }
      for (MethodElementForLink method in methods) {
        _containedNames[method.name] = method;
      }
    }
    return _containedNames.putIfAbsent(
        name, () => UndefinedElementForLink.instance);
  }

  @override
  FieldElement getField(String name) {
    for (FieldElement fieldElement in fields) {
      if (name == fieldElement.name) {
        return fieldElement;
      }
    }
    return null;
  }

  @override
  PropertyAccessorElement getGetter(String getterName) {
    for (PropertyAccessorElement accessor in accessors) {
      if (accessor.isGetter && accessor.name == getterName) {
        return accessor;
      }
    }
    return null;
  }

  @override
  MethodElement getMethod(String methodName) {
    for (MethodElement method in methods) {
      if (method.name == methodName) {
        return method;
      }
    }
    return null;
  }

  /**
   * Perform type inference and cycle detection on this class and
   * store the resulting information in [compilationUnit].
   */
  void link(CompilationUnitElementInBuildUnit compilationUnit);

  @override
  noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
}

/**
 * Element representing a class resynthesized from a summary during
 * linking.
 */
class ClassElementForLink_Class extends ClassElementForLink
    with TypeParameterizedElementMixin
    implements ClassElementImpl {
  /**
   * The unlinked representation of the class in the summary.
   */
  final UnlinkedClass _unlinkedClass;

  List<ConstructorElementForLink> _constructors;
  ConstructorElementForLink _unnamedConstructor;
  bool _unnamedConstructorComputed = false;
  List<FieldElementForLink_ClassField> _fields;
  InterfaceType _supertype;
  InterfaceType _type;
  List<MethodElementForLink> _methods;
  List<InterfaceType> _mixins;
  List<InterfaceType> _interfaces;
  List<PropertyAccessorElementForLink> _accessors;

  ClassElementForLink_Class(
      CompilationUnitElementForLink enclosingElement, this._unlinkedClass)
      : super(enclosingElement);

  @override
  List<PropertyAccessorElementForLink> get accessors {
    if (_accessors == null) {
      _accessors = <PropertyAccessorElementForLink>[];
      Map<String, SyntheticVariableElementForLink> syntheticVariables =
          <String, SyntheticVariableElementForLink>{};
      for (UnlinkedExecutable unlinkedExecutable
          in _unlinkedClass.executables) {
        if (unlinkedExecutable.kind == UnlinkedExecutableKind.getter ||
            unlinkedExecutable.kind == UnlinkedExecutableKind.setter) {
          String name = unlinkedExecutable.name;
          if (unlinkedExecutable.kind == UnlinkedExecutableKind.setter) {
            assert(name.endsWith('='));
            name = name.substring(0, name.length - 1);
          }
          SyntheticVariableElementForLink syntheticVariable = syntheticVariables
              .putIfAbsent(name, () => new SyntheticVariableElementForLink());
          PropertyAccessorElementForLink_Executable accessor =
              new PropertyAccessorElementForLink_Executable(enclosingElement,
                  this, unlinkedExecutable, syntheticVariable);
          _accessors.add(accessor);
          if (unlinkedExecutable.kind == UnlinkedExecutableKind.getter) {
            syntheticVariable._getter = accessor;
          } else {
            syntheticVariable._setter = accessor;
          }
        }
      }
      for (FieldElementForLink_ClassField field in fields) {
        _accessors.add(field.getter);
        if (!field.isConst && !field.isFinal) {
          _accessors.add(field.setter);
        }
      }
    }
    return _accessors;
  }

  @override
  List<ConstructorElementForLink> get constructors {
    if (_constructors == null) {
      _constructors = <ConstructorElementForLink>[];
      for (UnlinkedExecutable unlinkedExecutable
          in _unlinkedClass.executables) {
        if (unlinkedExecutable.kind == UnlinkedExecutableKind.constructor) {
          _constructors
              .add(new ConstructorElementForLink(this, unlinkedExecutable));
        }
      }
      if (_constructors.isEmpty) {
        _unnamedConstructorComputed = true;
        _unnamedConstructor = new ConstructorElementForLink_Synthetic(this);
        _constructors.add(_unnamedConstructor);
      }
    }
    return _constructors;
  }

  @override
  ContextForLink get context => enclosingUnit.context;

  @override
  String get displayName => _unlinkedClass.name;

  @override
  TypeParameterizedElementMixin get enclosingTypeParameterContext => null;

  @override
  List<FieldElementForLink_ClassField> get fields {
    if (_fields == null) {
      _fields = <FieldElementForLink_ClassField>[];
      for (UnlinkedVariable field in _unlinkedClass.fields) {
        _fields.add(new FieldElementForLink_ClassField(this, field));
      }
    }
    return _fields;
  }

  @override
  String get identifier => name;

  @override
  List<InterfaceType> get interfaces => _interfaces ??=
      _unlinkedClass.interfaces.map(_computeInterfaceType).toList();

  @override
  bool get isEnum => false;

  @override
  bool get isMixinApplication => _unlinkedClass.isMixinApplication;

  @override
  bool get isObject => _unlinkedClass.hasNoSupertype;

  @override
  LibraryElementForLink get library => enclosingElement.library;

  @override
  List<MethodElementForLink> get methods {
    if (_methods == null) {
      _methods = <MethodElementForLink>[];
      for (UnlinkedExecutable unlinkedExecutable
          in _unlinkedClass.executables) {
        if (unlinkedExecutable.kind ==
            UnlinkedExecutableKind.functionOrMethod) {
          _methods.add(new MethodElementForLink(this, unlinkedExecutable));
        }
      }
    }
    return _methods;
  }

  @override
  List<InterfaceType> get mixins =>
      _mixins ??= _unlinkedClass.mixins.map(_computeInterfaceType).toList();

  @override
  String get name => _unlinkedClass.name;

  @override
  InterfaceType get supertype {
    if (isObject) {
      return null;
    }
    return _supertype ??= _computeInterfaceType(_unlinkedClass.supertype);
  }

  @override
  InterfaceType get type =>
      _type ??= buildType((int i) => typeParameterTypes[i], null);

  @override
  List<UnlinkedTypeParam> get unlinkedTypeParams =>
      _unlinkedClass.typeParameters;

  @override
  ConstructorElementForLink get unnamedConstructor {
    if (!_unnamedConstructorComputed) {
      for (ConstructorElementForLink constructor in constructors) {
        if (constructor.name.isEmpty) {
          _unnamedConstructor = constructor;
          break;
        }
      }
      _unnamedConstructorComputed = true;
    }
    return _unnamedConstructor;
  }

  @override
  int get version => 0;

  @override
  DartType buildType(
      DartType getTypeArgument(int i), List<int> implicitFunctionTypeIndices) {
    int numTypeParameters = _unlinkedClass.typeParameters.length;
    if (numTypeParameters != 0) {
      List<DartType> typeArguments =
          new List<DartType>.generate(numTypeParameters, getTypeArgument);
      if (typeArguments.contains(null)) {
        return context.typeSystem.instantiateToBounds(this.type);
      } else {
        return new InterfaceTypeImpl.elementWithNameAndArgs(
            this, name, () => typeArguments);
      }
    } else {
      return _type ??= new InterfaceTypeImpl(this);
    }
  }

  @override
  void link(CompilationUnitElementInBuildUnit compilationUnit) {
    for (ConstructorElementForLink constructorElement in constructors) {
      constructorElement.link(compilationUnit);
    }
    if (library._linker.strongMode) {
      for (MethodElementForLink methodElement in methods) {
        methodElement.link(compilationUnit);
      }
      for (PropertyAccessorElementForLink propertyAccessorElement
          in accessors) {
        propertyAccessorElement.link(compilationUnit);
      }
      for (FieldElementForLink_ClassField fieldElement in fields) {
        fieldElement.link(compilationUnit);
      }
    }
  }

  @override
  String toString() => '$enclosingElement.$name';

  /**
   * Convert [typeRef] into an [InterfaceType].
   */
  InterfaceType _computeInterfaceType(EntityRef typeRef) {
    if (typeRef != null) {
      DartType type = enclosingElement.resolveTypeRef(typeRef, this);
      if (type is InterfaceType && !type.element.isEnum) {
        return type;
      }
      // In the event that the `typeRef` isn't an interface type (which may
      // happen in the event of erroneous code) just fall through and pretend
      // the supertype is `Object`.
    }
    return enclosingElement.enclosingElement._linker.typeProvider.objectType;
  }
}

/**
 * Element representing an enum resynthesized from a summary during
 * linking.
 */
class ClassElementForLink_Enum extends ClassElementForLink
    implements EnumElementImpl {
  /**
   * The unlinked representation of the enum in the summary.
   */
  final UnlinkedEnum _unlinkedEnum;

  InterfaceType _type;
  List<FieldElementForLink> _fields;
  List<PropertyAccessorElementForLink> _accessors;
  DartType _valuesType;

  ClassElementForLink_Enum(
      CompilationUnitElementForLink enclosingElement, this._unlinkedEnum)
      : super(enclosingElement);

  @override
  List<PropertyAccessorElementForLink> get accessors {
    if (_accessors == null) {
      _accessors = <PropertyAccessorElementForLink>[];
      for (FieldElementForLink field in fields) {
        _accessors.add(field.getter);
      }
    }
    return _accessors;
  }

  @override
  List<ConstructorElementForLink> get constructors => const [];

  @override
  String get displayName => _unlinkedEnum.name;

  @override
  List<FieldElementForLink> get fields {
    if (_fields == null) {
      _fields = <FieldElementForLink>[];
      _fields.add(new FieldElementForLink_EnumField_values(this));
      for (UnlinkedEnumValue value in _unlinkedEnum.values) {
        _fields.add(new FieldElementForLink_EnumField_value(this, value));
      }
      _fields.add(new FieldElementForLink_EnumField_index(this));
    }
    return _fields;
  }

  @override
  List<InterfaceType> get interfaces => const [];

  @override
  bool get isEnum => true;

  @override
  bool get isObject => false;

  @override
  List<MethodElementForLink> get methods => const [];

  @override
  List<InterfaceType> get mixins => const [];

  @override
  String get name => _unlinkedEnum.name;

  @override
  InterfaceType get supertype => library._linker.typeProvider.objectType;

  @override
  InterfaceType get type => _type ??= new InterfaceTypeImpl(this);

  @override
  List<TypeParameterElement> get typeParameters => const [];

  @override
  ConstructorElementForLink get unnamedConstructor => null;

  /**
   * Get the type of the enum's static member `values`.
   */
  DartType get valuesType =>
      _valuesType ??= library._linker.typeProvider.listType.instantiate([type]);

  @override
  DartType buildType(DartType getTypeArgument(int i),
          List<int> implicitFunctionTypeIndices) =>
      type;

  @override
  void link(CompilationUnitElementInBuildUnit compilationUnit) {}

  @override
  String toString() => '$enclosingElement.$name';
}

/**
 * Element representing a compilation unit resynthesized from a
 * summary during linking.
 */
abstract class CompilationUnitElementForLink
    implements CompilationUnitElementImpl, ResynthesizerContext {
  /**
   * The unlinked representation of the compilation unit in the
   * summary.
   */
  final UnlinkedUnit _unlinkedUnit;

  /**
   * For each entry in [UnlinkedUnit.references], the element referred
   * to by the reference, or `null` if it hasn't been located yet.
   */
  final List<ReferenceableElementForLink> _references;

  /**
   * The absolute URI of this compilation unit.
   */
  final String _absoluteUri;

  List<ClassElementForLink_Class> _types;
  Map<String, ReferenceableElementForLink> _containedNames;
  List<TopLevelVariableElementForLink> _topLevelVariables;
  List<ClassElementForLink_Enum> _enums;
  List<TopLevelFunctionElementForLink> _functions;
  List<PropertyAccessorElementForLink> _accessors;
  List<FunctionTypeAliasElementForLink> _functionTypeAliases;

  /**
   * Index of this unit in the list of units in the enclosing library.
   */
  final int unitNum;

  CompilationUnitElementForLink(UnlinkedUnit unlinkedUnit, this.unitNum,
      int numReferences, this._absoluteUri)
      : _references = new List<ReferenceableElementForLink>(numReferences),
        _unlinkedUnit = unlinkedUnit;

  @override
  List<PropertyAccessorElementForLink> get accessors {
    if (_accessors == null) {
      _accessors = <PropertyAccessorElementForLink>[];
      Map<String, SyntheticVariableElementForLink> syntheticVariables =
          <String, SyntheticVariableElementForLink>{};
      for (UnlinkedExecutable unlinkedExecutable in _unlinkedUnit.executables) {
        if (unlinkedExecutable.kind == UnlinkedExecutableKind.getter ||
            unlinkedExecutable.kind == UnlinkedExecutableKind.setter) {
          String name = unlinkedExecutable.name;
          if (unlinkedExecutable.kind == UnlinkedExecutableKind.setter) {
            assert(name.endsWith('='));
            name = name.substring(0, name.length - 1);
          }
          SyntheticVariableElementForLink syntheticVariable = syntheticVariables
              .putIfAbsent(name, () => new SyntheticVariableElementForLink());
          PropertyAccessorElementForLink_Executable accessor =
              new PropertyAccessorElementForLink_Executable(
                  this, null, unlinkedExecutable, syntheticVariable);
          _accessors.add(accessor);
          if (unlinkedExecutable.kind == UnlinkedExecutableKind.getter) {
            syntheticVariable._getter = accessor;
          } else {
            syntheticVariable._setter = accessor;
          }
        }
      }
      for (TopLevelVariableElementForLink variable in topLevelVariables) {
        _accessors.add(variable.getter);
        if (!variable.isConst && !variable.isFinal) {
          _accessors.add(variable.setter);
        }
      }
    }
    return _accessors;
  }

  @override
  ContextForLink get context => library.context;

  @override
  LibraryElementForLink get enclosingElement;

  @override
  List<ClassElementForLink_Enum> get enums {
    if (_enums == null) {
      _enums = <ClassElementForLink_Enum>[];
      for (UnlinkedEnum unlinkedEnum in _unlinkedUnit.enums) {
        _enums.add(new ClassElementForLink_Enum(this, unlinkedEnum));
      }
    }
    return _enums;
  }

  @override
  List<TopLevelFunctionElementForLink> get functions {
    if (_functions == null) {
      _functions = <TopLevelFunctionElementForLink>[];
      for (UnlinkedExecutable executable in _unlinkedUnit.executables) {
        if (executable.kind == UnlinkedExecutableKind.functionOrMethod) {
          _functions.add(new TopLevelFunctionElementForLink(this, executable));
        }
      }
    }
    return _functions;
  }

  @override
  List<FunctionTypeAliasElementForLink> get functionTypeAliases =>
      _functionTypeAliases ??= _unlinkedUnit.typedefs.map((UnlinkedTypedef t) {
        if (t.style == TypedefStyle.functionType) {
          return new FunctionTypeAliasElementForLink(this, t);
        } else if (t.style == TypedefStyle.genericFunctionType) {
          return new GenericTypeAliasElementForLink(this, t);
        }
      }).toList();

  @override
  String get identifier => _absoluteUri;

  /**
   * Indicates whether this compilation element is part of the build unit
   * currently being linked.
   */
  bool get isInBuildUnit;

  /**
   * Determine whether type inference is complete in this compilation unit.
   */
  bool get isTypeInferenceComplete {
    LibraryCycleForLink libraryCycleForLink = library.libraryCycleForLink;
    if (libraryCycleForLink == null) {
      return true;
    } else {
      return libraryCycleForLink._node.isEvaluated;
    }
  }

  @override
  LibraryElementForLink get library => enclosingElement;

  @override
  ResynthesizerContext get resynthesizerContext => this;

  @override
  List<TopLevelVariableElementForLink> get topLevelVariables {
    if (_topLevelVariables == null) {
      _topLevelVariables = <TopLevelVariableElementForLink>[];
      for (UnlinkedVariable unlinkedVariable in _unlinkedUnit.variables) {
        _topLevelVariables
            .add(new TopLevelVariableElementForLink(this, unlinkedVariable));
      }
    }
    return _topLevelVariables;
  }

  @override
  List<ClassElementForLink_Class> get types {
    if (_types == null) {
      _types = <ClassElementForLink_Class>[];
      for (UnlinkedClass unlinkedClass in _unlinkedUnit.classes) {
        _types.add(new ClassElementForLink_Class(this, unlinkedClass));
      }
    }
    return _types;
  }

  /**
   * The linked representation of the compilation unit in the summary.
   */
  LinkedUnit get _linkedUnit;

  /**
   * Search the unit for a top level element with the given [name].
   * If no name is found, return the singleton instance of
   * [UndefinedElementForLink].
   */
  ReferenceableElementForLink getContainedName(name) {
    if (_containedNames == null) {
      _containedNames = <String, ReferenceableElementForLink>{};
      // TODO(paulberry): what's the correct way to handle name conflicts?
      for (ClassElementForLink_Class type in types) {
        _containedNames[type.name] = type;
      }
      for (ClassElementForLink_Enum enm in enums) {
        _containedNames[enm.name] = enm;
      }
      for (TopLevelFunctionElementForLink function in functions) {
        _containedNames[function.name] = function;
      }
      for (PropertyAccessorElementForLink accessor in accessors) {
        _containedNames[accessor.name] = accessor;
      }
      for (FunctionTypeAliasElementForLink functionTypeAlias
          in functionTypeAliases) {
        _containedNames[functionTypeAlias.name] = functionTypeAlias;
      }
      // TODO(paulberry): fill in other top level entities (typedefs
      // and executables).
    }
    return _containedNames.putIfAbsent(
        name, () => UndefinedElementForLink.instance);
  }

  /**
   * Compute the type referred to by the given linked type [slot] (interpreted
   * relative to [typeParameterContext]).  If there is no inferred type in the
   * given slot, `dynamic` is returned.
   */
  DartType getLinkedType(
      int slot, TypeParameterizedElementMixin typeParameterContext);

  @override
  noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);

  /**
   * Return the class element for the constructor referred to by the given
   * [index] in [UnlinkedUnit.references].  If the reference is unresolved,
   * return [UndefinedElementForLink.instance].
   */
  ReferenceableElementForLink resolveConstructorClassRef(int index) {
    LinkedReference linkedReference = _linkedUnit.references[index];
    if (linkedReference.kind == ReferenceKind.classOrEnum) {
      return resolveRef(index);
    }
    if (index < _unlinkedUnit.references.length) {
      UnlinkedReference unlinkedReference = _unlinkedUnit.references[index];
      return resolveRef(unlinkedReference.prefixReference);
    }
    return UndefinedElementForLink.instance;
  }

  /**
   * Return the element referred to by the given [index] in
   * [UnlinkedUnit.references].  If the reference is unresolved,
   * return [UndefinedElementForLink.instance].
   */
  ReferenceableElementForLink resolveRef(int index) {
    if (_references[index] == null) {
      UnlinkedReference unlinkedReference =
          index < _unlinkedUnit.references.length
              ? _unlinkedUnit.references[index]
              : null;
      LinkedReference linkedReference = _linkedUnit.references[index];
      String name = unlinkedReference == null
          ? linkedReference.name
          : unlinkedReference.name;
      int containingReference = unlinkedReference == null
          ? linkedReference.containingReference
          : unlinkedReference.prefixReference;
      if (containingReference != 0 &&
          _linkedUnit.references[containingReference].kind !=
              ReferenceKind.prefix) {
        if (linkedReference.kind == ReferenceKind.function) {
          // Local function
          _references[index] = resolveRef(containingReference)
                  .getLocalFunction(linkedReference.localIndex) ??
              UndefinedElementForLink.instance;
        } else {
          _references[index] =
              resolveRef(containingReference).getContainedName(name);
        }
      } else if (linkedReference.dependency == 0) {
        if (name == 'void') {
          _references[index] = enclosingElement._linker.voidElement;
        } else if (name == '*bottom*') {
          _references[index] = enclosingElement._linker.bottomElement;
        } else if (name == 'dynamic') {
          _references[index] = enclosingElement._linker.dynamicElement;
        } else {
          _references[index] = enclosingElement.getContainedName(name);
        }
      } else {
        LibraryElementForLink dependency =
            enclosingElement._getDependency(linkedReference.dependency);
        _references[index] = dependency.getContainedName(name);
      }
    }
    return _references[index];
  }

  @override
  DartType resolveTypeRef(
      EntityRef type, TypeParameterizedElementMixin typeParameterContext,
      {bool defaultVoid: false,
      bool instantiateToBoundsAllowed: true,
      bool declaredType: false}) {
    if (type == null) {
      if (defaultVoid) {
        return VoidTypeImpl.instance;
      } else {
        return DynamicTypeImpl.instance;
      }
    }
    if (type.paramReference != 0) {
      return typeParameterContext.getTypeParameterType(type.paramReference);
    } else if (type.syntheticReturnType != null) {
      // TODO(paulberry): implement.
      throw new UnimplementedError();
    } else if (type.implicitFunctionTypeIndices.isNotEmpty) {
      // TODO(paulberry): implement.
      throw new UnimplementedError();
    } else {
      DartType getTypeArgument(int i) {
        if (i < type.typeArguments.length) {
          return resolveTypeRef(type.typeArguments[i], typeParameterContext);
        } else if (!instantiateToBoundsAllowed) {
          // Do not allow buildType to instantiate the bounds; force dynamic.
          return DynamicTypeImpl.instance;
        } else {
          return null;
        }
      }

      ReferenceableElementForLink element = resolveRef(type.reference);
      return element.buildType(
          getTypeArgument, type.implicitFunctionTypeIndices);
    }
  }

  @override
  String toString() => enclosingElement.toString();
}

/**
 * Element representing a compilation unit which is part of the build
 * unit being linked.
 */
class CompilationUnitElementInBuildUnit extends CompilationUnitElementForLink {
  @override
  final LinkedUnitBuilder _linkedUnit;

  @override
  final LibraryElementInBuildUnit enclosingElement;

  CompilationUnitElementInBuildUnit(
      this.enclosingElement,
      UnlinkedUnit unlinkedUnit,
      this._linkedUnit,
      int unitNum,
      String absoluteUri)
      : super(
            unlinkedUnit, unitNum, unlinkedUnit.references.length, absoluteUri);

  @override
  bool get isInBuildUnit => true;

  @override
  LibraryElementInBuildUnit get library => enclosingElement;

  /**
   * If this compilation unit already has a reference in its references table
   * matching [dependency], [name], [numTypeParameters], [unitNum],
   * [containingReference], and [kind], return its index.  Otherwise add a new reference to
   * the table and return its index.
   */
  int addRawReference(String name,
      {int dependency: 0,
      int numTypeParameters: 0,
      int unitNum: 0,
      int containingReference: 0,
      int localIndex: 0,
      ReferenceKind kind: ReferenceKind.classOrEnum}) {
    List<LinkedReferenceBuilder> linkedReferences = _linkedUnit.references;
    List<UnlinkedReference> unlinkedReferences = _unlinkedUnit.references;
    for (int i = 0; i < linkedReferences.length; i++) {
      LinkedReferenceBuilder linkedReference = linkedReferences[i];
      int candidateContainingReference = i < unlinkedReferences.length
          ? unlinkedReferences[i].prefixReference
          : linkedReference.containingReference;
      if (candidateContainingReference != 0 &&
          linkedReferences[candidateContainingReference].kind ==
              ReferenceKind.prefix) {
        // We don't need to match containing references when they are prefixes,
        // since the relevant information is in linkedReference.dependency.
        candidateContainingReference = 0;
      }
      if (linkedReference.dependency == dependency &&
          (i < unlinkedReferences.length
                  ? unlinkedReferences[i].name
                  : linkedReference.name) ==
              name &&
          linkedReference.numTypeParameters == numTypeParameters &&
          linkedReference.unit == unitNum &&
          candidateContainingReference == containingReference &&
          linkedReference.kind == kind &&
          linkedReference.localIndex == localIndex) {
        return i;
      }
    }
    int result = linkedReferences.length;
    linkedReferences.add(new LinkedReferenceBuilder(
        dependency: dependency,
        name: name,
        numTypeParameters: numTypeParameters,
        unit: unitNum,
        containingReference: containingReference,
        kind: kind,
        localIndex: localIndex));
    return result;
  }

  /**
   * If this compilation unit already has a reference in its references table
   * to [element], return its index.  Otherwise add a new reference to the table
   * and return its index.
   */
  int addReference(Element element) {
    if (element is ClassElementForLink) {
      return addRawReference(element.name,
          dependency: library.addDependency(element.library),
          numTypeParameters: element.typeParameters.length,
          unitNum: element.enclosingElement.unitNum);
    } else if (element is FunctionTypeAliasElementForLink) {
      return addRawReference(element.name,
          dependency: library.addDependency(element.library),
          numTypeParameters: element.typeParameters.length,
          unitNum: element.enclosingElement.unitNum,
          kind: ReferenceKind.typedef);
    } else if (element is FunctionElementForLink_Initializer) {
      return addRawReference('',
          containingReference: addReference(element.enclosingElement),
          kind: ReferenceKind.function,
          localIndex: 0);
    } else if (element is FunctionElementForLink_Local_NonSynthetic) {
      ExecutableElementForLink parent = element.enclosingElement;
      int localIndex = parent.functions.indexOf(element);
      assert(localIndex != -1);
      return addRawReference(element.name,
          containingReference: addReference(parent),
          kind: ReferenceKind.function,
          localIndex: localIndex);
    } else if (element is ExecutableElementForLink_NonLocal) {
      ClassElementForLink_Class enclosingClass = element.enclosingClass;
      ReferenceKind kind;
      switch (element._unlinkedExecutable.kind) {
        case UnlinkedExecutableKind.functionOrMethod:
          kind = enclosingClass != null
              ? ReferenceKind.method
              : ReferenceKind.topLevelFunction;
          break;
        case UnlinkedExecutableKind.setter:
          kind = ReferenceKind.propertyAccessor;
          break;
        default:
          // TODO(paulberry): implement other cases as necessary
          throw new UnimplementedError('${element._unlinkedExecutable.kind}');
      }
      if (enclosingClass == null) {
        return addRawReference(element.name,
            numTypeParameters: element.typeParameters.length,
            dependency:
                library.addDependency(element.library as LibraryElementForLink),
            unitNum: element.compilationUnit.unitNum,
            kind: kind);
      } else {
        return addRawReference(element.name,
            numTypeParameters: element.typeParameters.length,
            containingReference: addReference(enclosingClass),
            kind: kind);
      }
    } else if (element is FunctionElementForLink_Initializer) {
      return addRawReference('',
          containingReference: addReference(element.enclosingElement),
          kind: ReferenceKind.function);
    } else if (element is TopLevelVariableElementForLink) {
      return addRawReference(element.name,
          dependency: library.addDependency(element.library),
          unitNum: element.compilationUnit.unitNum,
          kind: ReferenceKind.topLevelPropertyAccessor);
    } else if (element is FieldElementForLink_ClassField) {
      ClassElementForLink_Class enclosingClass = element.enclosingElement;
      // Note: even if the class has type parameters, we don't need to set
      // numTypeParameters because numTypeParameters does not count type
      // parameters of parent elements (see
      // [LinkedReference.numTypeParameters]).
      return addRawReference(element.name,
          containingReference: addReference(enclosingClass),
          kind: ReferenceKind.propertyAccessor);
    }
    // TODO(paulberry): implement other cases
    throw new UnimplementedError('${element.runtimeType}');
  }

  @override
  DartType getLinkedType(
      int slot, TypeParameterizedElementMixin typeParameterContext) {
    // This method should only be called on compilation units that come from
    // dependencies, never on compilation units that are part of the current
    // build unit.
    throw new StateError(
        'Linker tried to access linked type from current build unit');
  }

  /**
   * Perform type inference and const cycle detection on this
   * compilation unit.
   */
  void link() {
    if (library._linker.strongMode) {
      new InstanceMemberInferrer(enclosingElement._linker.typeProvider,
              enclosingElement.inheritanceManager, new Set<FieldElement>())
          .inferCompilationUnit(this);
      for (TopLevelVariableElementForLink variable in topLevelVariables) {
        variable.link(this);
      }
    }
    for (ClassElementForLink classElement in types) {
      classElement.link(this);
    }
  }

  /**
   * Throw away any information stored in the summary by a previous call to
   * [link].
   */
  void unlink() {
    _linkedUnit.constCycles.clear();
    _linkedUnit.parametersInheritingCovariant.clear();
    _linkedUnit.references.length = _unlinkedUnit.references.length;
    _linkedUnit.types.clear();
  }

  /**
   * Store the fact that the given [slot] represents a constant constructor
   * that is part of a cycle.
   */
  void _storeConstCycle(int slot) {
    _linkedUnit.constCycles.add(slot);
  }

  /**
   * Store the fact that the given [slot] represents a parameter that inherits
   * `@covariant` behavior.
   */
  void _storeInheritsCovariant(int slot) {
    _linkedUnit.parametersInheritingCovariant.add(slot);
  }

  /**
   * Store the given [linkedType] in the given [slot] of the this compilation
   * unit's linked type list.
   */
  void _storeLinkedType(int slot, DartType linkedType,
      TypeParameterizedElementMixin typeParameterContext) {
    if (slot != 0) {
      if (linkedType != null && !linkedType.isDynamic) {
        _linkedUnit.types.add(_createLinkedType(
            linkedType, this, typeParameterContext,
            slot: slot));
      }
    }
  }

  /**
   * Store the given error [error] in the given [slot].
   */
  void _storeLinkedTypeError(int slot, TopLevelInferenceErrorBuilder error) {
    if (slot != 0) {
      if (error != null) {
        error.slot = slot;
        _linkedUnit.topLevelInferenceErrors.add(error);
      }
    }
  }
}

/**
 * Element representing a compilation unit which is depended upon
 * (either directly or indirectly) by the build unit being linked.
 *
 * TODO(paulberry): ensure that inferred types in dependencies are properly
 * resynthesized.
 */
class CompilationUnitElementInDependency extends CompilationUnitElementForLink {
  @override
  final LinkedUnit _linkedUnit;

  List<EntityRef> _linkedTypeRefs;

  @override
  final LibraryElementInDependency enclosingElement;

  CompilationUnitElementInDependency(
      this.enclosingElement,
      UnlinkedUnit unlinkedUnit,
      LinkedUnit linkedUnit,
      int unitNum,
      String absoluteUri)
      : _linkedUnit = linkedUnit,
        super(
            unlinkedUnit, unitNum, linkedUnit.references.length, absoluteUri) {
    // Make one pass through the linked types to determine the lengths for
    // _linkedTypeRefs and _linkedTypes.  TODO(paulberry): add an int to the
    // summary to make this unnecessary.
    int maxLinkedTypeSlot = 0;
    for (EntityRef ref in _linkedUnit.types) {
      if (ref.slot > maxLinkedTypeSlot) {
        maxLinkedTypeSlot = ref.slot;
      }
    }
    // Initialize _linkedTypeRefs.
    _linkedTypeRefs = new List<EntityRef>(maxLinkedTypeSlot + 1);
    for (EntityRef ref in _linkedUnit.types) {
      _linkedTypeRefs[ref.slot] = ref;
    }
  }

  @override
  bool get isInBuildUnit => false;

  @override
  DartType getLinkedType(
      int slot, TypeParameterizedElementMixin typeParameterContext) {
    if (slot < _linkedTypeRefs.length) {
      return resolveTypeRef(_linkedTypeRefs[slot], typeParameterContext);
    } else {
      return DynamicTypeImpl.instance;
    }
  }
}

/**
 * Instance of [ConstNode] representing a constant constructor.
 */
class ConstConstructorNode extends ConstNode {
  /**
   * The [ConstructorElement] to which this node refers.
   */
  final ConstructorElementForLink constructorElement;

  /**
   * Once this node has been evaluated, indicates whether the
   * constructor is free of constant evaluation cycles.
   */
  bool isCycleFree = false;

  ConstConstructorNode(this.constructorElement);

  @override
  List<ConstNode> computeDependencies() {
    List<ConstNode> dependencies = <ConstNode>[];
    void safeAddDependency(ConstNode target) {
      if (target != null) {
        dependencies.add(target);
      }
    }

    UnlinkedExecutable unlinkedExecutable =
        constructorElement._unlinkedExecutable;
    ClassElementForLink_Class enclosingClass =
        constructorElement.enclosingElement;
    ConstructorElementForLink redirectedConstructor =
        _getFactoryRedirectedConstructor();
    if (redirectedConstructor != null) {
      if (redirectedConstructor._constNode != null) {
        safeAddDependency(redirectedConstructor._constNode);
      }
    } else if (unlinkedExecutable.isFactory) {
      // Factory constructor, but getConstRedirectedConstructor returned
      // null.  This can happen if we're visiting one of the special external
      // const factory constructors in the SDK, or if the code contains
      // errors (such as delegating to a non-const constructor, or delegating
      // to a constructor that can't be resolved).  In any of these cases,
      // we'll evaluate calls to this constructor without having to refer to
      // any other constants.  So we don't need to report any dependencies.
    } else {
      ClassElementForLink superClass = enclosingClass.supertype?.element;
      bool defaultSuperInvocationNeeded = true;
      for (UnlinkedConstructorInitializer constructorInitializer
          in constructorElement._unlinkedExecutable.constantInitializers) {
        if (constructorInitializer.kind ==
            UnlinkedConstructorInitializerKind.superInvocation) {
          defaultSuperInvocationNeeded = false;
          if (superClass != null && !superClass.isObject) {
            ConstructorElementForLink constructor = superClass
                .getContainedName(constructorInitializer.name)
                .asConstructor;
            safeAddDependency(constructor?._constNode);
          }
        } else if (constructorInitializer.kind ==
            UnlinkedConstructorInitializerKind.thisInvocation) {
          defaultSuperInvocationNeeded = false;
          ConstructorElementForLink constructor = constructorElement
              .enclosingClass
              .getContainedName(constructorInitializer.name)
              .asConstructor;
          safeAddDependency(constructor?._constNode);
        }
        CompilationUnitElementForLink compilationUnit =
            constructorElement.enclosingElement.enclosingElement;
        collectDependencies(
            dependencies, constructorInitializer.expression, compilationUnit);
        for (UnlinkedExpr unlinkedConst in constructorInitializer.arguments) {
          collectDependencies(dependencies, unlinkedConst, compilationUnit);
        }
      }

      if (defaultSuperInvocationNeeded) {
        // No explicit superconstructor invocation found, so we need to
        // manually insert a reference to the implicit superconstructor.
        if (superClass != null && !superClass.isObject) {
          ConstructorElementForLink unnamedConstructor =
              superClass.unnamedConstructor;
          safeAddDependency(unnamedConstructor?._constNode);
        }
      }
      for (FieldElementForLink field in enclosingClass.fields) {
        // Note: non-static const isn't allowed but we handle it anyway so
        // that we won't be confused by incorrect code.
        if ((field.isFinal || field.isConst) && !field.isStatic) {
          safeAddDependency(field.getter.asConstVariable);
        }
      }
      for (ParameterElementForLink parameterElement
          in constructorElement.parameters) {
        safeAddDependency(parameterElement._constNode);
      }
    }
    return dependencies;
  }

  /**
   * If [constructorElement] redirects to another constructor via a factory
   * redirect, return the constructor it redirects to.
   */
  ConstructorElementForLink _getFactoryRedirectedConstructor() {
    EntityRef redirectedConstructor =
        constructorElement._unlinkedExecutable.redirectedConstructor;
    if (redirectedConstructor != null) {
      return constructorElement.compilationUnit
          .resolveRef(redirectedConstructor.reference)
          .asConstructor;
    } else {
      return null;
    }
  }
}

/**
 * Specialization of [DependencyWalker] for detecting constant
 * evaluation cycles.
 */
class ConstDependencyWalker extends DependencyWalker<ConstNode> {
  @override
  void evaluate(ConstNode v) {
    if (v is ConstConstructorNode) {
      v.isCycleFree = true;
    }
    v.isEvaluated = true;
  }

  @override
  void evaluateScc(List<ConstNode> scc) {
    for (ConstNode v in scc) {
      if (v is ConstConstructorNode) {
        v.isCycleFree = false;
      }
      v.isEvaluated = true;
    }
  }
}

/**
 * Specialization of [Node] used to construct the constant evaluation
 * dependency graph.
 */
abstract class ConstNode extends Node<ConstNode> {
  @override
  bool isEvaluated = false;

  /**
   * Collect the dependencies in [unlinkedConst] (which should be
   * interpreted relative to [compilationUnit]) and store them in
   * [dependencies].
   */
  void collectDependencies(
      List<ConstNode> dependencies,
      UnlinkedExpr unlinkedConst,
      CompilationUnitElementForLink compilationUnit) {
    if (unlinkedConst == null) {
      return;
    }
    int refPtr = 0;
    int intPtr = 0;
    for (UnlinkedExprOperation operation in unlinkedConst.operations) {
      switch (operation) {
        case UnlinkedExprOperation.pushInt:
          intPtr++;
          break;
        case UnlinkedExprOperation.pushLongInt:
          int numInts = unlinkedConst.ints[intPtr++];
          intPtr += numInts;
          break;
        case UnlinkedExprOperation.concatenate:
          intPtr++;
          break;
        case UnlinkedExprOperation.pushReference:
          EntityRef ref = unlinkedConst.references[refPtr++];
          ConstVariableNode variable =
              compilationUnit.resolveRef(ref.reference).asConstVariable;
          if (variable != null) {
            dependencies.add(variable);
          }
          break;
        case UnlinkedExprOperation.makeUntypedList:
        case UnlinkedExprOperation.makeUntypedMap:
          intPtr++;
          break;
        case UnlinkedExprOperation.assignToRef:
          refPtr++;
          break;
        case UnlinkedExprOperation.invokeMethodRef:
          EntityRef ref = unlinkedConst.references[refPtr++];
          ConstVariableNode variable =
              compilationUnit.resolveRef(ref.reference).asConstVariable;
          if (variable != null) {
            dependencies.add(variable);
          }
          intPtr += 2;
          int numTypeArguments = unlinkedConst.ints[intPtr++];
          refPtr += numTypeArguments;
          break;
        case UnlinkedExprOperation.invokeMethod:
          intPtr += 2;
          int numTypeArguments = unlinkedConst.ints[intPtr++];
          refPtr += numTypeArguments;
          break;
        case UnlinkedExprOperation.makeTypedList:
          refPtr++;
          intPtr++;
          break;
        case UnlinkedExprOperation.makeTypedMap:
          refPtr += 2;
          intPtr++;
          break;
        case UnlinkedExprOperation.invokeConstructor:
          EntityRef ref = unlinkedConst.references[refPtr++];
          ConstructorElementForLink element =
              compilationUnit.resolveRef(ref.reference).asConstructor;
          if (element?._constNode != null) {
            dependencies.add(element._constNode);
          }
          intPtr += 2;
          break;
        case UnlinkedExprOperation.typeCast:
        case UnlinkedExprOperation.typeCheck:
          refPtr++;
          break;
        case UnlinkedExprOperation.pushLocalFunctionReference:
          intPtr += 2;
          break;
        default:
          break;
      }
    }
    assert(refPtr == unlinkedConst.references.length);
    assert(intPtr == unlinkedConst.ints.length);
  }
}

/**
 * Instance of [ConstNode] representing a parameter with a default
 * value.
 */
class ConstParameterNode extends ConstNode {
  /**
   * The [ParameterElement] to which this node refers.
   */
  final ParameterElementForLink parameterElement;

  ConstParameterNode(this.parameterElement);

  @override
  List<ConstNode> computeDependencies() {
    List<ConstNode> dependencies = <ConstNode>[];
    collectDependencies(
        dependencies,
        parameterElement._unlinkedParam.initializer?.bodyExpr,
        parameterElement.compilationUnit);
    return dependencies;
  }
}

/**
 * Element representing a constructor resynthesized from a summary
 * during linking.
 */
class ConstructorElementForLink extends ExecutableElementForLink_NonLocal
    with ReferenceableElementForLink
    implements ConstructorElementImpl {
  /**
   * If this is a `const` constructor and the enclosing library is
   * part of the build unit being linked, the constructor's node in
   * the constant evaluation dependency graph.  Otherwise `null`.
   */
  ConstConstructorNode _constNode;

  ConstructorElementForLink(ClassElementForLink_Class enclosingClass,
      UnlinkedExecutable unlinkedExecutable)
      : super(enclosingClass.enclosingElement, enclosingClass,
            unlinkedExecutable) {
    if (enclosingClass.enclosingElement.isInBuildUnit &&
        _unlinkedExecutable != null &&
        _unlinkedExecutable.constCycleSlot != 0) {
      _constNode = new ConstConstructorNode(this);
    }
  }

  @override
  ConstructorElementForLink get asConstructor => this;

  @override
  ClassElementImpl get enclosingElement => super.enclosingClass;

  @override
  String get identifier => name;

  @override
  bool get isCycleFree {
    if (!_constNode.isEvaluated) {
      new ConstDependencyWalker().walk(_constNode);
    }
    return _constNode.isCycleFree;
  }

  @override
  DartType get returnType => enclosingElement.type;

  @override
  List<TypeParameterElement> get typeParameters => const [];

  /**
   * Perform const cycle detection on this constructor.
   */
  void link(CompilationUnitElementInBuildUnit compilationUnit) {
    if (_constNode != null && !isCycleFree) {
      compilationUnit._storeConstCycle(_unlinkedExecutable.constCycleSlot);
    }
    // TODO(paulberry): call super.
  }

  @override
  noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
}

/**
 * A synthetic constructor.
 */
class ConstructorElementForLink_Synthetic extends ConstructorElementForLink {
  ConstructorElementForLink_Synthetic(
      ClassElementForLink_Class enclosingElement)
      : super(enclosingElement, null);

  @override
  String get name => '';

  @override
  List<ParameterElement> get parameters => const <ParameterElement>[];
}

/**
 * Instance of [ConstNode] representing a constant field or constant
 * top level variable.
 */
class ConstVariableNode extends ConstNode {
  /**
   * The [FieldElement] or [TopLevelVariableElement] to which this
   * node refers.
   */
  final VariableElementForLink variableElement;

  ConstVariableNode(this.variableElement);

  @override
  List<ConstNode> computeDependencies() {
    List<ConstNode> dependencies = <ConstNode>[];
    collectDependencies(
        dependencies,
        variableElement.unlinkedVariable.initializer?.bodyExpr,
        variableElement.compilationUnit);
    return dependencies;
  }
}

/**
 * Stub implementation of [AnalysisContext] which provides just those methods
 * needed during linking.
 */
class ContextForLink implements AnalysisContext {
  final Linker _linker;

  ContextForLink(this._linker);

  @override
  AnalysisOptionsForLink get analysisOptions => _linker.analysisOptions;

  @override
  TypeSystem get typeSystem => _linker.typeSystem;

  @override
  noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
}

/**
 * Base class for executable elements resynthesized from a summary during
 * linking.
 */
abstract class ExecutableElementForLink extends Object
    with TypeParameterizedElementMixin, ParameterParentElementForLink
    implements ExecutableElementImpl {
  /**
   * The unlinked representation of the method in the summary.
   */
  final UnlinkedExecutable _unlinkedExecutable;

  DartType _declaredReturnType;
  DartType _inferredReturnType;
  FunctionTypeImpl _type;
  String _name;
  String _displayName;

  final CompilationUnitElementForLink compilationUnit;

  ExecutableElementForLink(this.compilationUnit, this._unlinkedExecutable);

  @override
  ContextForLink get context => compilationUnit.context;

  /**
   * If the executable element had an explicitly declared return type, return
   * it.  Otherwise return `null`.
   */
  DartType get declaredReturnType {
    if (_unlinkedExecutable.returnType == null) {
      return null;
    } else {
      return _declaredReturnType ??=
          compilationUnit.resolveTypeRef(_unlinkedExecutable.returnType, this);
    }
  }

  @override
  String get displayName {
    if (_displayName == null) {
      _displayName = _unlinkedExecutable.name;
      if (_unlinkedExecutable.kind == UnlinkedExecutableKind.setter) {
        _displayName = _displayName.substring(0, _displayName.length - 1);
      }
    }
    return _displayName;
  }

  @override
  CompilationUnitElementImpl get enclosingUnit => compilationUnit;

  @override
  bool get hasImplicitReturnType => _unlinkedExecutable.returnType == null;

  @override
  List<int> get implicitFunctionTypeIndices => const <int>[];

  /**
   * Return the inferred return type of the executable element.  Should only be
   * called if no return type was explicitly declared.
   */
  DartType get inferredReturnType {
    // We should only try to infer a return type when none is explicitly
    // declared.
    assert(_unlinkedExecutable.returnType == null);
    if (Linker._initializerTypeInferenceCycle != null &&
        Linker._initializerTypeInferenceCycle ==
            compilationUnit.library.libraryCycleForLink) {
      // We are currently computing the type of an initializer expression in the
      // current library cycle, so type inference results should be ignored.
      return _computeDefaultReturnType();
    }
    if (_inferredReturnType == null) {
      if (_unlinkedExecutable.kind == UnlinkedExecutableKind.constructor) {
        // TODO(paulberry): implement.
        throw new UnimplementedError();
      } else if (compilationUnit.isInBuildUnit) {
        _inferredReturnType = _computeDefaultReturnType();
      } else {
        _inferredReturnType = compilationUnit.getLinkedType(
            _unlinkedExecutable.inferredReturnTypeSlot, this);
      }
    }
    return _inferredReturnType;
  }

  @override
  bool get isStatic => _unlinkedExecutable.isStatic;

  @override
  bool get isSynthetic => false;

  @override
  LibraryElement get library => enclosingElement.library;

  @override
  String get name {
    if (_name == null) {
      _name = _unlinkedExecutable.name;
      if (_name == '-' && _unlinkedExecutable.parameters.isEmpty) {
        _name = 'unary-';
      }
    }
    return _name;
  }

  @override
  DartType get returnType => declaredReturnType ?? inferredReturnType;

  @override
  void set returnType(DartType inferredType) {
    assert(_inferredReturnType == null);
    _inferredReturnType = inferredType;
  }

  @override
  FunctionTypeImpl get type => _type ??= new FunctionTypeImpl(this);

  @override
  TypeParameterizedElementMixin get typeParameterContext => this;

  @override
  List<UnlinkedParam> get unlinkedParameters => _unlinkedExecutable.parameters;

  @override
  List<UnlinkedTypeParam> get unlinkedTypeParams =>
      _unlinkedExecutable.typeParameters;

  @override
  bool isAccessibleIn(LibraryElement library) =>
      !Identifier.isPrivateName(name) || identical(this.library, library);

  /**
   * Compute the default return type for this type of executable element (if no
   * return type is declared and strong mode type inference cannot infer a
   * better return type).
   */
  DartType _computeDefaultReturnType() {
    if (_unlinkedExecutable.kind == UnlinkedExecutableKind.setter &&
        (library as LibraryElementForLink)._linker.strongMode) {
      // In strong mode, setters without an explicit return type are
      // considered to return `void`.
      return VoidTypeImpl.instance;
    } else {
      return DynamicTypeImpl.instance;
    }
  }
}

/**
 * Base class for executable elements that are resynthesized from a summary
 * during linking and are not local functions.
 */
abstract class ExecutableElementForLink_NonLocal
    extends ExecutableElementForLink {
  /**
   * Return the class in which this executable appears, maybe `null` for a
   * top-level function.
   */
  final ClassElementForLink_Class enclosingClass;

  ExecutableElementForLink_NonLocal(
      CompilationUnitElementForLink compilationUnit,
      this.enclosingClass,
      UnlinkedExecutable unlinkedExecutable)
      : super(compilationUnit, unlinkedExecutable);

  @override
  Element get enclosingElement => enclosingClass ?? compilationUnit;

  @override
  TypeParameterizedElementMixin get enclosingTypeParameterContext =>
      enclosingClass;

  /**
   * Store the results of type inference for this method in [compilationUnit].
   */
  void link(CompilationUnitElementInBuildUnit compilationUnit) {
    if (_unlinkedExecutable.returnType == null) {
      compilationUnit._storeLinkedType(
          _unlinkedExecutable.inferredReturnTypeSlot, inferredReturnType, this);
    }
    for (ParameterElementForLink parameterElement in parameters) {
      parameterElement.link(compilationUnit);
    }
  }
}

class ExprTypeComputer {
  final FunctionElementForLink_Local function;
  final CompilationUnitElementForLink unit;
  final LibraryElementForLink library;
  final Linker linker;
  final TypeProvider typeProvider;
  final UnlinkedExpr unlinkedConst;

  final List<DartType> stack = <DartType>[];
  int intPtr = 0;
  int refPtr = 0;
  int strPtr = 0;
  int assignmentOperatorPtr = 0;

  TopLevelInferenceErrorKind errorKind;

  factory ExprTypeComputer(FunctionElementForLink_Local functionElement) {
    CompilationUnitElementForLink unit = functionElement.compilationUnit;
    LibraryElementForLink library = unit.enclosingElement;
    Linker linker = library._linker;
    TypeProvider typeProvider = linker.typeProvider;
    UnlinkedExpr unlinkedConst = functionElement._unlinkedExecutable.bodyExpr;
    return new ExprTypeComputer._(
        functionElement, unit, library, linker, typeProvider, unlinkedConst);
  }

  ExprTypeComputer._(this.function, this.unit, this.library, this.linker,
      this.typeProvider, this.unlinkedConst);

  DartType compute() {
    if (unlinkedConst == null) {
      // No function body was stored for this function, so we can't infer its
      // return type.  Assume `dynamic`.
      return DynamicTypeImpl.instance;
    }
    // If no operations, we cannot compute the type.  Assume `dynamic`.
    if (unlinkedConst.operations.isEmpty) {
      return DynamicTypeImpl.instance;
    }
    // Perform RPN evaluation of the constant, using a stack of inferred types.
    for (UnlinkedExprOperation operation in unlinkedConst.operations) {
      switch (operation) {
        case UnlinkedExprOperation.pushInt:
          intPtr++;
          stack.add(typeProvider.intType);
          break;
        case UnlinkedExprOperation.pushLongInt:
          int numInts = _getNextInt();
          intPtr += numInts;
          stack.add(typeProvider.intType);
          break;
        case UnlinkedExprOperation.pushDouble:
          stack.add(typeProvider.doubleType);
          break;
        case UnlinkedExprOperation.pushTrue:
        case UnlinkedExprOperation.pushFalse:
          stack.add(typeProvider.boolType);
          break;
        case UnlinkedExprOperation.pushString:
          strPtr++;
          stack.add(typeProvider.stringType);
          break;
        case UnlinkedExprOperation.concatenate:
          stack.length -= _getNextInt();
          stack.add(typeProvider.stringType);
          break;
        case UnlinkedExprOperation.makeSymbol:
          strPtr++;
          stack.add(typeProvider.symbolType);
          break;
        case UnlinkedExprOperation.pushNull:
          stack.add(typeProvider.nullType);
          break;
        case UnlinkedExprOperation.pushSuper:
          stack.add(DynamicTypeImpl.instance);
          break;
        case UnlinkedExprOperation.pushThis:
          stack.add(DynamicTypeImpl.instance);
          break;
        case UnlinkedExprOperation.pushReference:
          try {
            _doPushReference();
          } on _InferenceFailedError {
            errorKind = TopLevelInferenceErrorKind.instanceGetter;
            return DynamicTypeImpl.instance;
          }
          break;
        case UnlinkedExprOperation.extractProperty:
          try {
            _doExtractProperty();
          } on _InferenceFailedError {
            errorKind = TopLevelInferenceErrorKind.instanceGetter;
            return DynamicTypeImpl.instance;
          }
          break;
        case UnlinkedExprOperation.invokeConstructor:
          _doInvokeConstructor();
          break;
        case UnlinkedExprOperation.makeUntypedList:
          _doMakeUntypedList();
          break;
        case UnlinkedExprOperation.makeUntypedMap:
          _doMakeUntypedMap();
          break;
        case UnlinkedExprOperation.makeTypedList:
          _doMakeTypedList();
          break;
        case UnlinkedExprOperation.makeTypedMap:
          _doMakeTypeMap();
          break;
        case UnlinkedExprOperation.not:
          stack.length -= 1;
          stack.add(typeProvider.boolType);
          break;
        case UnlinkedExprOperation.complement:
          _computePrefixExpressionType('~');
          break;
        case UnlinkedExprOperation.negate:
          _computePrefixExpressionType('unary-');
          break;
        case UnlinkedExprOperation.and:
        case UnlinkedExprOperation.or:
        case UnlinkedExprOperation.equal:
        case UnlinkedExprOperation.notEqual:
          stack.length -= 2;
          stack.add(typeProvider.boolType);
          break;
        case UnlinkedExprOperation.bitXor:
          _computeBinaryExpressionType(TokenType.CARET);
          break;
        case UnlinkedExprOperation.bitAnd:
          _computeBinaryExpressionType(TokenType.AMPERSAND);
          break;
        case UnlinkedExprOperation.bitOr:
          _computeBinaryExpressionType(TokenType.BAR);
          break;
        case UnlinkedExprOperation.bitShiftRight:
          _computeBinaryExpressionType(TokenType.GT_GT);
          break;
        case UnlinkedExprOperation.bitShiftLeft:
          _computeBinaryExpressionType(TokenType.LT_LT);
          break;
        case UnlinkedExprOperation.add:
          _computeBinaryExpressionType(TokenType.PLUS);
          break;
        case UnlinkedExprOperation.subtract:
          _computeBinaryExpressionType(TokenType.MINUS);
          break;
        case UnlinkedExprOperation.multiply:
          _computeBinaryExpressionType(TokenType.STAR);
          break;
        case UnlinkedExprOperation.divide:
          _computeBinaryExpressionType(TokenType.SLASH);
          break;
        case UnlinkedExprOperation.floorDivide:
          _computeBinaryExpressionType(TokenType.TILDE_SLASH);
          break;
        case UnlinkedExprOperation.greater:
          _computeBinaryExpressionType(TokenType.GT);
          break;
        case UnlinkedExprOperation.less:
          _computeBinaryExpressionType(TokenType.LT);
          break;
        case UnlinkedExprOperation.greaterEqual:
          _computeBinaryExpressionType(TokenType.GT_EQ);
          break;
        case UnlinkedExprOperation.lessEqual:
          _computeBinaryExpressionType(TokenType.LT_EQ);
          break;
        case UnlinkedExprOperation.modulo:
          _computeBinaryExpressionType(TokenType.PERCENT);
          break;
        case UnlinkedExprOperation.conditional:
          _doConditional();
          break;
        case UnlinkedExprOperation.assignToIndex:
        case UnlinkedExprOperation.assignToProperty:
        case UnlinkedExprOperation.assignToRef:
          errorKind = TopLevelInferenceErrorKind.assignment;
          return DynamicTypeImpl.instance;
        case UnlinkedExprOperation.await:
          _doAwait();
          break;
        case UnlinkedExprOperation.extractIndex:
          _doExtractIndex();
          break;
        case UnlinkedExprOperation.invokeMethodRef:
          try {
            _doInvokeMethodRef();
          } on _InferenceFailedError {
            errorKind = TopLevelInferenceErrorKind.instanceGetter;
            return DynamicTypeImpl.instance;
          }
          break;
        case UnlinkedExprOperation.invokeMethod:
          _doInvokeMethod();
          break;
        case UnlinkedExprOperation.cascadeSectionBegin:
          stack.add(stack.last);
          break;
        case UnlinkedExprOperation.cascadeSectionEnd:
          stack.removeLast();
          break;
        case UnlinkedExprOperation.typeCast:
          stack.removeLast();
          DartType type = _getNextTypeRef();
          stack.add(type);
          break;
        case UnlinkedExprOperation.typeCheck:
          stack.removeLast();
          refPtr++;
          stack.add(typeProvider.boolType);
          break;
        case UnlinkedExprOperation.throwException:
          stack.removeLast();
          stack.add(BottomTypeImpl.instance);
          break;
        case UnlinkedExprOperation.pushLocalFunctionReference:
          int popCount = _getNextInt();
          assert(popCount == 0); // TODO(paulberry): handle the nonzero case.
          stack.add(function.functions[_getNextInt()].type);
          break;
        case UnlinkedExprOperation.pushParameter:
          stack.add(_findParameterType(_getNextString()));
          break;
        case UnlinkedExprOperation.ifNull:
          _doIfNull();
          break;
        default:
          // TODO(paulberry): implement.
          throw new UnimplementedError('$operation');
      }
    }
    assert(intPtr == unlinkedConst.ints.length);
    assert(refPtr == unlinkedConst.references.length);
    assert(strPtr == unlinkedConst.strings.length);
    assert(assignmentOperatorPtr == unlinkedConst.assignmentOperators.length);
    assert(stack.length == 1);
    return stack[0];
  }

  void _computeBinaryExpressionType(TokenType operator) {
    DartType right = stack.removeLast();
    DartType left = stack.removeLast();
    _pushBinaryOperatorType(left, operator, right);
  }

  void _computePrefixExpressionType(String operatorName) {
    DartType operand = stack.removeLast();
    if (operand is InterfaceType) {
      MethodElement method =
          operand.lookUpInheritedMethod(operatorName, library: library);
      if (method != null) {
        DartType type = method.returnType;
        stack.add(type);
        return;
      }
    }
    stack.add(DynamicTypeImpl.instance);
  }

  void _doAwait() {
    DartType type = stack.removeLast();
    DartType typeArgument = type?.flattenFutures(linker.typeSystem);
    typeArgument = _dynamicIfNull(typeArgument);
    stack.add(typeArgument);
  }

  void _doConditional() {
    DartType elseType = stack.removeLast();
    DartType thenType = stack.removeLast();
    stack.removeLast();
    DartType type = _leastUpperBound(thenType, elseType);
    type = _dynamicIfNull(type);
    stack.add(type);
  }

  void _doExtractIndex() {
    stack.removeLast(); // index
    DartType target = stack.removeLast();
    stack.add(() {
      if (target is InterfaceType) {
        MethodElement method =
            target.lookUpInheritedMethod('[]', library: library);
        if (method != null) {
          return method.returnType;
        }
      }
      return DynamicTypeImpl.instance;
    }());
  }

  void _doExtractProperty() {
    DartType target = stack.removeLast();
    if (target.isDynamic) {
      target = typeProvider.objectType;
    }
    String propertyName = _getNextString();
    stack.add(() {
      if (target is InterfaceType) {
        ExecutableElement element = target
            .lookUpInheritedGetterOrMethod(propertyName, library: library);
        if (element != null) {
          _throwIfInstanceFieldOrAccessor(element);
          if (element is PropertyAccessorElement) {
            return element.returnType;
          } else {
            // Method tear-off
            return element.type;
          }
        }
      }
      return DynamicTypeImpl.instance;
    }());
  }

  void _doIfNull() {
    DartType secondType = stack.removeLast();
    DartType firstType = stack.removeLast();
    DartType type = _leastUpperBound(firstType, secondType);
    type = _dynamicIfNull(type);
    stack.add(type);
  }

  void _doInvokeConstructor() {
    int numNamed = unlinkedConst.ints[intPtr++];
    int numPositional = unlinkedConst.ints[intPtr++];
    List<String> namedArgNames = _getNextStrings(numNamed);
    List<DartType> namedArgTypeList = _popList(numNamed);
    List<DartType> positionalArgTypes = _popList(numPositional);

    EntityRef ref = _getNextRef();
    ReferenceableElementForLink refElement = unit.resolveRef(ref.reference);
    ConstructorElementForLink constructorElement = refElement.asConstructor;

    if (constructorElement != null) {
      stack.add(() {
        if (ref.typeArguments.isNotEmpty) {
          return constructorElement.enclosingClass.buildType((int i) {
            if (i < ref.typeArguments.length) {
              return unit.resolveTypeRef(
                  ref.typeArguments[i], function.typeParameterContext);
            } else {
              return null;
            }
          }, const <int>[]);
        } else {
          FunctionType rawType = StaticTypeAnalyzer
              .constructorToGenericFunctionType(constructorElement);
          FunctionType inferredType = _inferExecutableType(
              rawType,
              numNamed,
              numPositional,
              namedArgNames,
              namedArgTypeList,
              positionalArgTypes, const <DartType>[]);
          if (inferredType == null || identical(inferredType, rawType)) {
            inferredType = linker.typeSystem.instantiateToBounds(rawType);
          }
          return inferredType.returnType;
        }
      }());
    } else {
      ClassElementForLink classElement =
          unit.resolveConstructorClassRef(ref.reference).asClass;
      DartType inferredType;
      if (classElement != null) {
        InterfaceType rawType = classElement.type;
        inferredType = linker.typeSystem.instantiateToBounds(rawType);
      } else {
        inferredType = DynamicTypeImpl.instance;
      }
      stack.add(inferredType);
    }
  }

  void _doInvokeMethod() {
    int numNamed = unlinkedConst.ints[intPtr++];
    int numPositional = unlinkedConst.ints[intPtr++];
    List<String> namedArgNames = _getNextStrings(numNamed);
    List<DartType> namedArgTypeList = _popList(numNamed);
    List<DartType> positionalArgTypes = _popList(numPositional);
    // TODO(scheglov) if we pushed target and method name first, we might be
    // able to move work with arguments in _inferExecutableType()
    String methodName = _getNextString();
    List<DartType> typeArguments = _getTypeArguments();
    DartType target = stack.removeLast();
    if (target.isDynamic) {
      target = typeProvider.objectType;
    }
    stack.add(() {
      if (target is InterfaceType) {
        MethodElement method =
            target.lookUpInheritedMethod(methodName, library: library);
        FunctionType rawType = method?.type;
        FunctionType inferredType = _inferExecutableType(
            rawType,
            numNamed,
            numPositional,
            namedArgNames,
            namedArgTypeList,
            positionalArgTypes,
            typeArguments);
        if (inferredType != null) {
          return inferredType.returnType;
        }
      }
      return DynamicTypeImpl.instance;
    }());
  }

  void _doInvokeMethodRef() {
    int numNamed = _getNextInt();
    int numPositional = _getNextInt();
    List<String> namedArgNames = _getNextStrings(numNamed);
    List<DartType> namedArgTypeList = _popList(numNamed);
    List<DartType> positionalArgTypes = _popList(numPositional);
    EntityRef ref = _getNextRef();
    ReferenceableElementForLink element = unit.resolveRef(ref.reference);
    _throwIfInstanceFieldOrAccessor(element);
    List<DartType> typeArguments = _getTypeArguments();
    stack.add(() {
      DartType rawType = element.asStaticType;
      if (rawType is FunctionType) {
        FunctionType inferredType = _inferExecutableType(
            rawType,
            numNamed,
            numPositional,
            namedArgNames,
            namedArgTypeList,
            positionalArgTypes,
            typeArguments);
        if (inferredType != null) {
          return inferredType.returnType;
        }
      }
      return DynamicTypeImpl.instance;
    }());
  }

  void _doMakeTypedList() {
    DartType itemType = _getNextTypeRef();
    stack.length -= _getNextInt();
    stack.add(typeProvider.listType.instantiate(<DartType>[itemType]));
  }

  void _doMakeTypeMap() {
    DartType keyType = _getNextTypeRef();
    DartType valueType = _getNextTypeRef();
    stack.length -= 2 * _getNextInt();
    stack.add(typeProvider.mapType.instantiate(<DartType>[keyType, valueType]));
  }

  void _doMakeUntypedList() {
    int numItems = _getNextInt();
    DartType itemType = numItems == 0
        ? DynamicTypeImpl.instance
        : _popList(numItems).reduce(_leastUpperBound);
    itemType = _dynamicIfNull(itemType);
    stack.add(typeProvider.listType.instantiate(<DartType>[itemType]));
  }

  void _doMakeUntypedMap() {
    int numEntries = _getNextInt();
    List<DartType> keysValues = _popList(2 * numEntries);
    DartType keyType = null;
    DartType valueType = null;
    for (int i = 0; i < 2 * numEntries; i++) {
      DartType type = keysValues[i];
      if (i.isEven) {
        keyType = keyType == null ? type : _leastUpperBound(keyType, type);
      } else {
        valueType =
            valueType == null ? type : _leastUpperBound(valueType, type);
      }
    }
    keyType = _dynamicIfNull(keyType);
    valueType = _dynamicIfNull(valueType);
    stack.add(typeProvider.mapType.instantiate(<DartType>[keyType, valueType]));
  }

  void _doPushReference() {
    EntityRef ref = _getNextRef();
    if (ref.paramReference != 0) {
      stack.add(typeProvider.typeType);
    } else {
      // Synthetic function types can't be directly referred
      // to by expressions.
      assert(ref.syntheticReturnType == null);
      // Nor can implicit function types derived from
      // function-typed parameters.
      assert(ref.implicitFunctionTypeIndices.isEmpty);
      ReferenceableElementForLink element = unit.resolveRef(ref.reference);
      _throwIfInstanceFieldOrAccessor(element);
      stack.add(element.asStaticType);
    }
  }

  /**
   * Find the parameter in scope called [parameterName] and return its type.
   */
  DartType _findParameterType(String parameterName) {
    FunctionElementForLink_Local f = this.function;
    while (true) {
      for (ParameterElement parameter in f.parameters) {
        if (parameter.name == parameterName) {
          return parameter.type;
        }
      }
      Element parent = f.enclosingElement;
      if (parent is FunctionElementForLink_Local) {
        f = parent;
      } else {
        // Parameter not found.  This should never happen in a well-formed
        // summary.
        assert(false);
        return DynamicTypeImpl.instance;
      }
    }
  }

  int _getNextInt() {
    return unlinkedConst.ints[intPtr++];
  }

  EntityRef _getNextRef() => unlinkedConst.references[refPtr++];

  String _getNextString() {
    return unlinkedConst.strings[strPtr++];
  }

  List<String> _getNextStrings(int n) {
    List<String> result = new List<String>(n);
    for (int i = 0; i < n; i++) {
      result[i] = _getNextString();
    }
    return result;
  }

  DartType _getNextTypeRef() {
    EntityRef ref = _getNextRef();
    return unit.resolveTypeRef(ref, function.typeParameterContext);
  }

  List<DartType> _getTypeArguments() {
    int numTypeArguments = _getNextInt();
    List<DartType> typeArguments = new List<DartType>(numTypeArguments);
    for (int i = 0; i < numTypeArguments; i++) {
      typeArguments[i] = _getNextTypeRef();
    }
    return typeArguments;
  }

  FunctionType _inferExecutableType(
      FunctionType rawMethodType,
      int numNamedArguments,
      int numPositionalArguments,
      List<String> namedArgNames,
      List<DartType> namedArgTypeList,
      List<DartType> positionalArgTypes,
      List<DartType> typeArguments) {
    TypeSystem ts = linker.typeSystem;
    if (rawMethodType != null) {
      if (rawMethodType.typeFormals.isNotEmpty && typeArguments.isNotEmpty) {
        Element methodElement = rawMethodType.element;
        if (methodElement is TypeParameterizedElement &&
            methodElement.typeParameters.length == typeArguments.length) {
          return rawMethodType.instantiate(typeArguments);
        }
      } else if (rawMethodType.typeFormals.isNotEmpty &&
          ts is StrongTypeSystemImpl) {
        // Prepare the named argument types map.
        Map<String, DartType> namedArgTypes = <String, DartType>{};
        for (int i = 0; i < numNamedArguments; i++) {
          String name = namedArgNames[i];
          DartType type = namedArgTypeList[i];
          namedArgTypes[name] = type;
        }

        // Fill parameters and the corresponding arguments.
        List<ParameterElement> parameters = <ParameterElement>[];
        List<DartType> argumentTypes = <DartType>[];
        int positionalIndex = 0;
        int numRequiredParameters = 0;
        for (ParameterElement parameter in rawMethodType.parameters) {
          if (parameter.parameterKind == ParameterKind.REQUIRED) {
            numRequiredParameters++;
            if (numRequiredParameters > numPositionalArguments) {
              return null;
            }
            parameters.add(parameter);
            argumentTypes.add(positionalArgTypes[positionalIndex]);
            positionalIndex++;
          } else if (parameter.parameterKind == ParameterKind.POSITIONAL) {
            if (positionalIndex < numPositionalArguments) {
              parameters.add(parameter);
              argumentTypes.add(positionalArgTypes[positionalIndex]);
              positionalIndex++;
            }
          } else if (parameter.parameterKind == ParameterKind.NAMED) {
            DartType namedArgumentType = namedArgTypes[parameter.name];
            if (namedArgumentType != null) {
              parameters.add(parameter);
              argumentTypes.add(namedArgumentType);
            }
          }
        }

        // Perform inference.
        FunctionType inferred = ts.inferGenericFunctionOrType(
            rawMethodType, parameters, argumentTypes, null);
        return inferred;
      }
    }
    // Not a generic function type, use the raw type.
    return rawMethodType;
  }

  DartType _leastUpperBound(DartType s, DartType t) {
    return linker.typeSystem.getLeastUpperBound(s, t);
  }

  List<DartType> _popList(int n) {
    List<DartType> result = stack.sublist(stack.length - n, stack.length);
    stack.length -= n;
    return result;
  }

  void _pushBinaryOperatorType(
      DartType left, TokenType operator, DartType right) {
    if (left is InterfaceType) {
      MethodElement method =
          left.lookUpInheritedMethod(operator.lexeme, library: library);
      if (method != null) {
        DartType type = method.returnType;
        type = linker.typeSystem
            .refineBinaryExpressionType(left, operator, right, type);
        stack.add(type);
        return;
      }
    }
    stack.add(DynamicTypeImpl.instance);
  }

  void _throwIfInstanceFieldOrAccessor(Object element) {
    if (element is NonstaticMemberElementForLink &&
            element.hasInstanceGetterReference ||
        element is FieldElement && !element.isStatic ||
        element is PropertyAccessorElement && !element.isStatic) {
      throw new _InferenceFailedError(
          'Instance fields cannot be used for type inference.');
    }
  }
}

/**
 * Element representing a field resynthesized from a summary during
 * linking.
 */
abstract class FieldElementForLink implements FieldElement {
  @override
  PropertyAccessorElementForLink get getter;

  @override
  PropertyAccessorElementForLink get setter;
}

/**
 * Specialization of [FieldElementForLink] for class fields.
 */
class FieldElementForLink_ClassField extends VariableElementForLink
    implements FieldElementForLink {
  @override
  final ClassElementForLink_Class enclosingElement;

  /**
   * If this is an instance field, the type that was computed by
   * [InstanceMemberInferrer] (if any).  Otherwise `null`.
   */
  DartType _inferredInstanceType;

  TopLevelInferenceErrorBuilder _inferenceError;

  FieldElementForLink_ClassField(ClassElementForLink_Class enclosingElement,
      UnlinkedVariable unlinkedVariable)
      : enclosingElement = enclosingElement,
        super(unlinkedVariable, enclosingElement.enclosingElement);

  @override
  bool get isStatic => unlinkedVariable.isStatic;

  @override
  void set type(DartType inferredType) {
    assert(!isStatic);
    assert(_inferredInstanceType == null);
    _inferredInstanceType = inferredType;
  }

  @override
  TypeParameterizedElementMixin get _typeParameterContext => enclosingElement;

  /**
   * Store the results of type inference for this field in
   * [compilationUnit].
   */
  void link(CompilationUnitElementInBuildUnit compilationUnit) {
    if (hasImplicitType) {
      compilationUnit._storeLinkedType(
          unlinkedVariable.inferredTypeSlot,
          isStatic ? inferredType : _inferredInstanceType,
          _typeParameterContext);
      compilationUnit._storeLinkedTypeError(
          unlinkedVariable.inferredTypeSlot, _inferenceError);
      if (initializer != null) {
        compilationUnit._storeLinkedTypeError(
            unlinkedVariable.inferredTypeSlot, initializer._inferenceError);
        initializer.link(compilationUnit);
      }
    }
  }

  void setInferenceError(TopLevelInferenceErrorBuilder error) {
    assert(_inferenceError == null);
    _inferenceError = error;
  }

  @override
  String toString() => '$enclosingElement.$name';
}

/**
 * Specialization of [FieldElementForLink] for enum fields.
 */
class FieldElementForLink_EnumField extends FieldElementForLink
    implements FieldElement {
  PropertyAccessorElementForLink_EnumField _getter;

  @override
  final ClassElementForLink_Enum enclosingElement;

  FieldElementForLink_EnumField(this.enclosingElement);

  @override
  PropertyAccessorElementForLink_EnumField get getter =>
      _getter ??= new PropertyAccessorElementForLink_EnumField(this);

  @override
  bool get isSynthetic => false;

  @override
  noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);

  @override
  String toString() => '$enclosingElement.$name';
}

/**
 * Specialization of [FieldElementForLink] for the 'index' enum field.
 */
class FieldElementForLink_EnumField_index
    extends FieldElementForLink_EnumField {
  FieldElementForLink_EnumField_index(ClassElementForLink_Enum enclosingElement)
      : super(enclosingElement);

  @override
  bool get isStatic => false;

  @override
  String get name => 'index';

  @override
  DartType get type =>
      enclosingElement.enclosingElement.library._linker.typeProvider.intType;
}

/**
 * Specialization of [FieldElementForLink] for enum fields.
 */
class FieldElementForLink_EnumField_value
    extends FieldElementForLink_EnumField {
  /**
   * The unlinked representation of the field in the summary.
   */
  final UnlinkedEnumValue unlinkedEnumValue;

  FieldElementForLink_EnumField_value(
      ClassElementForLink_Enum enclosingElement, this.unlinkedEnumValue)
      : super(enclosingElement);

  @override
  bool get isStatic => true;

  @override
  String get name => unlinkedEnumValue.name;

  @override
  DartType get type => enclosingElement.type;
}

/**
 * Specialization of [FieldElementForLink] for the 'values' enum field.
 */
class FieldElementForLink_EnumField_values
    extends FieldElementForLink_EnumField {
  FieldElementForLink_EnumField_values(
      ClassElementForLink_Enum enclosingElement)
      : super(enclosingElement);

  @override
  bool get isStatic => true;

  @override
  String get name => 'values';

  @override
  DartType get type => enclosingElement.valuesType;
}

class FieldFormalParameterElementForLink extends ParameterElementForLink
    implements FieldFormalParameterElement {
  FieldElement _field;
  DartType _type;

  FieldFormalParameterElementForLink(
      ParameterParentElementForLink enclosingElement,
      UnlinkedParam unlinkedParam,
      TypeParameterizedElementMixin typeParameterContext,
      CompilationUnitElementForLink compilationUnit,
      int parameterIndex)
      : super(enclosingElement, unlinkedParam, typeParameterContext,
            compilationUnit, parameterIndex);

  @override
  FieldElement get field {
    if (_field == null) {
      Element enclosingConstructor = enclosingElement;
      if (enclosingConstructor is ConstructorElement) {
        Element enclosingClass = enclosingConstructor.enclosingElement;
        if (enclosingClass is ClassElement) {
          FieldElement field = enclosingClass.getField(_unlinkedParam.name);
          if (field != null && !field.isSynthetic) {
            _field = field;
          }
        }
      }
    }
    return _field;
  }

  @override
  bool get isInitializingFormal => true;

  @override
  DartType get type {
    return _type ??= field?.type ?? DynamicTypeImpl.instance;
  }
}

/**
 * Element representing a function-typed parameter resynthesied from a summary
 * during linking.
 */
class FunctionElementForLink_FunctionTypedParam extends Object
    with ParameterParentElementForLink
    implements FunctionElement {
  @override
  final ParameterElementForLink enclosingElement;

  @override
  final TypeParameterizedElementMixin typeParameterContext;

  @override
  final List<UnlinkedParam> unlinkedParameters;

  DartType _returnType;
  List<int> _implicitFunctionTypeIndices;

  FunctionElementForLink_FunctionTypedParam(this.enclosingElement,
      this.typeParameterContext, this.unlinkedParameters);

  @override
  List<int> get implicitFunctionTypeIndices {
    if (_implicitFunctionTypeIndices == null) {
      _implicitFunctionTypeIndices = enclosingElement
          .enclosingElement.implicitFunctionTypeIndices
          .toList();
      _implicitFunctionTypeIndices.add(enclosingElement._parameterIndex);
    }
    return _implicitFunctionTypeIndices;
  }

  @override
  DartType get returnType {
    if (_returnType == null) {
      if (enclosingElement._unlinkedParam.type == null) {
        _returnType = DynamicTypeImpl.instance;
      } else {
        _returnType = enclosingElement.compilationUnit.resolveTypeRef(
            enclosingElement._unlinkedParam.type, typeParameterContext);
      }
    }
    return _returnType;
  }

  @override
  List<TypeParameterElement> get typeParameters => const [];

  @override
  noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
}

/**
 * Element representing the initializer expression of a variable.
 */
class FunctionElementForLink_Initializer extends Object
    with ReferenceableElementForLink, TypeParameterizedElementMixin
    implements FunctionElementForLink_Local {
  /**
   * The variable for which this element is the initializer.
   */
  final VariableElementForLink _variable;

  /**
   * The type inference node for this function, or `null` if it hasn't been
   * computed yet.
   */
  TypeInferenceNode _typeInferenceNode;

  List<FunctionElementForLink_Local_NonSynthetic> _functions;
  DartType _inferredReturnType;
  TopLevelInferenceErrorBuilder _inferenceError;

  FunctionElementForLink_Initializer(this._variable);

  @override
  TypeInferenceNode get asTypeInferenceNode =>
      _typeInferenceNode ??= new TypeInferenceNode(this);

  @override
  CompilationUnitElementForLink get compilationUnit =>
      _variable.compilationUnit;

  @override
  VariableElementForLink get enclosingElement => _variable;

  TypeParameterizedElementMixin get enclosingTypeParameterContext =>
      _variable.enclosingElement is ClassElementForLink
          ? _variable.enclosingElement
          : null;

  @override
  CompilationUnitElementForLink get enclosingUnit => _variable.compilationUnit;

  @override
  List<FunctionElementForLink_Local_NonSynthetic> get functions =>
      _functions ??= _variable.unlinkedVariable.initializer.localFunctions
          .map((UnlinkedExecutable ex) =>
              new FunctionElementForLink_Local_NonSynthetic(
                  _variable.compilationUnit, this, ex))
          .toList();

  @override
  String get identifier => '';

  @override
  bool get isAsynchronous => _unlinkedExecutable.isAsynchronous;

  @override
  DartType get returnType {
    // If this is a variable whose type needs inferring, infer it.
    if (_variable.hasImplicitType) {
      return _variable.inferredType;
    } else {
      // There's no reason linking should need to access the type of
      // this FunctionElement, since the variable doesn't need its
      // type inferred.
      assert(false);
      // But for robustness, return the dynamic type.
      return DynamicTypeImpl.instance;
    }
  }

  @override
  void set returnType(DartType newType) {
    // InstanceMemberInferrer stores the new type both here and on the variable
    // element.  We don't need to record both values, so we ignore it here.
  }

  @override
  TypeParameterizedElementMixin get typeParameterContext => this;

  @override
  List<UnlinkedTypeParam> get unlinkedTypeParams => const [];

  @override
  bool get _hasTypeBeenInferred => _inferredReturnType != null;

  @override
  UnlinkedExecutable get _unlinkedExecutable =>
      _variable.unlinkedVariable.initializer;

  @override
  FunctionElementForLink_Local getLocalFunction(int index) {
    List<FunctionElementForLink_Local_NonSynthetic> functions = this.functions;
    return index < functions.length ? functions[index] : null;
  }

  /**
   * Store the results of type inference for this initializer in
   * [compilationUnit].
   */
  void link(CompilationUnitElementInBuildUnit compilationUnit) {
    compilationUnit._storeLinkedType(_unlinkedExecutable.inferredReturnTypeSlot,
        _inferredReturnType, typeParameterContext);
    for (FunctionElementForLink_Local_NonSynthetic function in functions) {
      function.link(compilationUnit);
    }
  }

  @override
  noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);

  @override
  void _setInferenceError(TopLevelInferenceErrorBuilder error) {
    assert(!_hasTypeBeenInferred);
    _inferenceError = error;
  }

  @override
  void _setInferredType(DartType type) {
    assert(!_hasTypeBeenInferred);
    _inferredReturnType = type;
    _variable._inferredType = _dynamicIfNull(type);
  }
}

/**
 * Element representing a local function (possibly a closure).
 */
abstract class FunctionElementForLink_Local
    implements
        ExecutableElementForLink,
        FunctionElementImpl,
        ReferenceableElementForLink {
  /**
   * Indicates whether type inference has completed for this function.
   */
  bool get _hasTypeBeenInferred;

  /**
   * Stores the given [error] as the type inference error for this function.
   * Should only be called if [_hasTypeBeenInferred] is `false`.
   */
  void _setInferenceError(TopLevelInferenceErrorBuilder error);

  /**
   * Stores the given [type] as the inferred return type for this function.
   * Should only be called if [_hasTypeBeenInferred] is `false`.
   */
  void _setInferredType(DartType type);
}

/**
 * Element representing a local function (possibly a closure) inside another
 * executable.
 */
class FunctionElementForLink_Local_NonSynthetic extends ExecutableElementForLink
    with ReferenceableElementForLink
    implements FunctionElementForLink_Local {
  @override
  final ExecutableElementForLink enclosingElement;

  List<FunctionElementForLink_Local_NonSynthetic> _functions;

  /**
   * The type inference node for this function, or `null` if it hasn't been
   * computed yet.
   */
  TypeInferenceNode _typeInferenceNode;

  FunctionElementForLink_Local_NonSynthetic(
      CompilationUnitElementForLink compilationUnit,
      this.enclosingElement,
      UnlinkedExecutable unlinkedExecutable)
      : super(compilationUnit, unlinkedExecutable);

  @override
  TypeInferenceNode get asTypeInferenceNode =>
      _typeInferenceNode ??= new TypeInferenceNode(this);

  @override
  TypeParameterizedElementMixin get enclosingTypeParameterContext =>
      enclosingElement;

  @override
  List<FunctionElementForLink_Local_NonSynthetic> get functions =>
      _functions ??= _unlinkedExecutable.localFunctions
          .map((UnlinkedExecutable ex) =>
              new FunctionElementForLink_Local_NonSynthetic(
                  compilationUnit, this, ex))
          .toList();

  @override
  String get identifier {
    String identifier = _unlinkedExecutable.name;
    Element enclosing = this.enclosingElement;
    if (enclosing is ExecutableElement) {
      int id =
          ElementImpl.findElementIndexUsingIdentical(enclosing.functions, this);
      identifier += "@$id";
    }
    return identifier;
  }

  @override
  bool get isAsynchronous => _unlinkedExecutable.isAsynchronous;

  @override
  bool get _hasTypeBeenInferred => _inferredReturnType != null;

  @override
  DartType buildType(
      DartType getTypeArgument(int i), List<int> implicitFunctionTypeIndices) {
    assert(implicitFunctionTypeIndices.isEmpty);
    return type;
  }

  @override
  FunctionElementForLink_Local getLocalFunction(int index) {
    List<FunctionElementForLink_Local_NonSynthetic> functions = this.functions;
    return index < functions.length ? functions[index] : null;
  }

  /**
   * Store the results of type inference for this function in [compilationUnit].
   */
  void link(CompilationUnitElementInBuildUnit compilationUnit) {
    if (_unlinkedExecutable.returnType == null) {
      compilationUnit._storeLinkedType(
          _unlinkedExecutable.inferredReturnTypeSlot, inferredReturnType, this);
    }
    for (FunctionElementForLink_Local_NonSynthetic function in functions) {
      function.link(compilationUnit);
    }
  }

  @override
  noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);

  @override
  void _setInferenceError(TopLevelInferenceErrorBuilder error) {}

  @override
  void _setInferredType(DartType type) {