pkg/kernel/lib/ast.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.

/// -----------------------------------------------------------------------
///                          WHEN CHANGING THIS FILE:
/// -----------------------------------------------------------------------
///
/// If you are adding/removing/modifying fields/classes of the AST, you must
/// also update the following files:
///
///   - binary/ast_to_binary.dart
///   - binary/ast_from_binary.dart
///   - text/ast_to_text.dart
///   - clone.dart
///   - binary.md
///   - type_checker.dart (if relevant)
///
/// -----------------------------------------------------------------------
///                           ERROR HANDLING
/// -----------------------------------------------------------------------
///
/// As a rule of thumb, errors that can be detected statically are handled by
/// the frontend, typically by translating the erroneous code into a 'throw' or
/// a call to 'noSuchMethod'.
///
/// For example, there are no arity mismatches in static invocations, and
/// there are no direct invocations of a constructor on a abstract class.
///
/// -----------------------------------------------------------------------
///                           STATIC vs TOP-LEVEL
/// -----------------------------------------------------------------------
///
/// The term `static` includes both static class members and top-level members.
///
/// "Static class member" is the preferred term for non-top level statics.
///
/// Static class members are not lifted to the library level because mirrors
/// and stack traces can observe that they are class members.
///
/// -----------------------------------------------------------------------
///                                 PROCEDURES
/// -----------------------------------------------------------------------
///
/// "Procedure" is an umbrella term for method, getter, setter, index-getter,
/// index-setter, operator overloader, and factory constructor.
///
/// Generative constructors, field initializers, local functions are NOT
/// procedures.
///
/// -----------------------------------------------------------------------
///                               TRANSFORMATIONS
/// -----------------------------------------------------------------------
///
/// AST transformations can be performed using [TreeNode.replaceWith] or the
/// [Transformer] visitor class.
///
/// Use [Transformer] for bulk transformations that are likely to transform lots
/// of nodes, and [TreeNode.replaceWith] for sparse transformations that mutate
/// relatively few nodes.  Or use whichever is more convenient.
///
/// The AST can also be mutated by direct field manipulation, but the user then
/// has to update parent pointers manually.
///
library kernel.ast;

import 'dart:core';
import 'dart:collection' show ListBase;
import 'dart:convert' show utf8;

import 'visitor.dart';
export 'visitor.dart';

import 'canonical_name.dart' show CanonicalName, Reference;
export 'canonical_name.dart' show CanonicalName, Reference;

import 'default_language_version.dart' show defaultLanguageVersion;
export 'default_language_version.dart' show defaultLanguageVersion;

import 'transformations/flags.dart';
import 'text/ast_to_text.dart' as astToText;
import 'core_types.dart';
import 'type_algebra.dart';
import 'type_environment.dart';
import 'src/assumptions.dart';
import 'src/non_null.dart';
import 'src/printer.dart';
import 'src/text_util.dart';

/// Any type of node in the IR.
abstract class Node {
  const Node();

  R accept<R>(Visitor<R> v);
  void visitChildren(Visitor v);

  /// Returns the textual representation of this node for use in debugging.
  ///
  /// [toString] should only be used for debugging, but should not leak.
  ///
  /// The data is generally bare-bones, but can easily be updated for your
  /// specific debugging needs.
  String toString();

  /// Returns the textual representation of this node for use in debugging.
  ///
  /// [toStringInternal] should only be used for debugging, but should not leak.
  ///
  /// The data is generally bare-bones, but can easily be updated for your
  /// specific debugging needs.
  ///
  /// This method is called internally by toString methods to create conciser
  /// textual representations.
  String toStringInternal() => toText(defaultAstTextStrategy);

  /// Returns the textual representation of this node for use in debugging.
  ///
  /// Note that this adds some nodes to a static map to ensure consistent
  /// naming, but that it thus also leaks memory. [leakingDebugToString] should
  /// thus only be used for debugging and short-running test tools.
  ///
  /// Synthetic names are cached globally to retain consistency across different
  /// [leakingDebugToString] calls (hence the memory leak).
  String leakingDebugToString() => astToText.debugNodeToString(this);

  String toText(AstTextStrategy strategy) {
    AstPrinter printer = new AstPrinter(strategy);
    toTextInternal(printer);
    return printer.getText();
  }

  void toTextInternal(AstPrinter printer);
}

/// A mutable AST node with a parent pointer.
///
/// This is anything other than [Name] and [DartType] nodes.
abstract class TreeNode extends Node {
  static int _hashCounter = 0;
  final int hashCode = _hashCounter = (_hashCounter + 1) & 0x3fffffff;
  static const int noOffset = -1;

  TreeNode? parent;

  /// Offset in the source file it comes from.
  ///
  /// Valid values are from 0 and up, or -1 ([noOffset]) if the file offset is
  /// not available (this is the default if none is specifically set).
  int fileOffset = noOffset;

  R accept<R>(TreeVisitor<R> v);
  R accept1<R, A>(TreeVisitor1<R, A> v, A arg);
  void visitChildren(Visitor v);
  void transformChildren(Transformer v);
  void transformOrRemoveChildren(RemovingTransformer v);

  /// Replaces [child] with [replacement].
  ///
  /// The caller is responsible for ensuring that the AST remains a tree.  In
  /// particular, [replacement] should be an orphan or be part of an orphaned
  /// subtree.
  ///
  /// Has no effect if [child] is not actually a child of this node.
  ///
  /// [replacement] must be non-null.
  void replaceChild(TreeNode child, TreeNode replacement) {
    // ignore: unnecessary_null_comparison
    assert(replacement != null);
    transformChildren(new _ChildReplacer(child, replacement));
  }

  /// Inserts another node in place of this one.
  ///
  /// The caller is responsible for ensuring that the AST remains a tree.  In
  /// particular, [replacement] should be an orphan or be part of an orphaned
  /// subtree.
  ///
  /// [replacement] must be non-null.
  void replaceWith(TreeNode replacement) {
    // ignore: unnecessary_null_comparison
    assert(replacement != null);
    parent!.replaceChild(this, replacement);
    parent = null;
  }

  // TODO(johnniwinther): Make this non-nullable.
  Component? get enclosingComponent => parent?.enclosingComponent;

  /// Returns the best known source location of the given AST node, or `null` if
  /// the node is orphaned.
  ///
  /// This getter is intended for diagnostics and debugging, and should be
  /// avoided in production code.
  Location? get location {
    if (fileOffset == noOffset) return parent?.location;
    return _getLocationInEnclosingFile(fileOffset);
  }

  Location? _getLocationInEnclosingFile(int offset) {
    return parent?._getLocationInEnclosingFile(offset);
  }
}

/// An AST node that can be referenced by other nodes.
///
/// There is a single [reference] belonging to this node, providing a level of
/// indirection that is needed during serialization.
abstract class NamedNode extends TreeNode {
  final Reference reference;

  NamedNode(Reference? reference)
      : this.reference = reference ?? new Reference() {
    if (this is Field) {
      (this as Field).getterReference.node = this;
    } else {
      this.reference.node = this;
    }
  }

  /// This is an advanced feature.
  ///
  /// See [Component.relink] for a comprehensive description.
  ///
  /// Makes sure the reference in this named node points to itself.
  void _relinkNode() {
    this.reference.node = this;
  }
}

abstract class FileUriNode extends TreeNode {
  /// The URI of the source file this node was loaded from.
  Uri get fileUri;
}

abstract class Annotatable extends TreeNode {
  List<Expression> get annotations;
  void addAnnotation(Expression node);
}

// ------------------------------------------------------------------------
//                      LIBRARIES and CLASSES
// ------------------------------------------------------------------------

enum NonNullableByDefaultCompiledMode { Weak, Strong, Agnostic, Invalid }

class Library extends NamedNode
    implements Annotatable, Comparable<Library>, FileUriNode {
  /// An import path to this library.
  ///
  /// The [Uri] should have the `dart`, `package`, `app`, or `file` scheme.
  ///
  /// If the URI has the `app` scheme, it is relative to the application root.
  Uri importUri;

  /// The URI of the source file this library was loaded from.
  @override
  Uri fileUri;

  Version? _languageVersion;
  Version get languageVersion => _languageVersion ?? defaultLanguageVersion;

  void setLanguageVersion(Version languageVersion) {
    // ignore: unnecessary_null_comparison
    if (languageVersion == null) {
      throw new StateError("Trying to set language version 'null'");
    }
    _languageVersion = languageVersion;
  }

  static const int SyntheticFlag = 1 << 0;
  static const int NonNullableByDefaultFlag = 1 << 1;
  static const int NonNullableByDefaultModeBit1 = 1 << 2;
  static const int NonNullableByDefaultModeBit2 = 1 << 3;

  int flags = 0;

  /// If true, the library is synthetic, for instance library that doesn't
  /// represents an actual file and is created as the result of error recovery.
  bool get isSynthetic => flags & SyntheticFlag != 0;
  void set isSynthetic(bool value) {
    flags = value ? (flags | SyntheticFlag) : (flags & ~SyntheticFlag);
  }

  bool get isNonNullableByDefault => (flags & NonNullableByDefaultFlag) != 0;
  void set isNonNullableByDefault(bool value) {
    flags = value
        ? (flags | NonNullableByDefaultFlag)
        : (flags & ~NonNullableByDefaultFlag);
  }

  NonNullableByDefaultCompiledMode get nonNullableByDefaultCompiledMode {
    bool bit1 = (flags & NonNullableByDefaultModeBit1) != 0;
    bool bit2 = (flags & NonNullableByDefaultModeBit2) != 0;
    if (!bit1 && !bit2) return NonNullableByDefaultCompiledMode.Weak;
    if (bit1 && !bit2) return NonNullableByDefaultCompiledMode.Strong;
    if (bit1 && bit2) return NonNullableByDefaultCompiledMode.Agnostic;
    if (!bit1 && bit2) return NonNullableByDefaultCompiledMode.Invalid;
    throw new StateError("Unused bit-pattern for compilation mode");
  }

  void set nonNullableByDefaultCompiledMode(
      NonNullableByDefaultCompiledMode mode) {
    switch (mode) {
      case NonNullableByDefaultCompiledMode.Weak:
        flags = (flags & ~NonNullableByDefaultModeBit1) &
            ~NonNullableByDefaultModeBit2;
        break;
      case NonNullableByDefaultCompiledMode.Strong:
        flags = (flags | NonNullableByDefaultModeBit1) &
            ~NonNullableByDefaultModeBit2;
        break;
      case NonNullableByDefaultCompiledMode.Agnostic:
        flags = (flags | NonNullableByDefaultModeBit1) |
            NonNullableByDefaultModeBit2;
        break;
      case NonNullableByDefaultCompiledMode.Invalid:
        flags = (flags & ~NonNullableByDefaultModeBit1) |
            NonNullableByDefaultModeBit2;
        break;
    }
  }

  String? name;

  /// Problems in this [Library] encoded as json objects.
  ///
  /// Note that this field can be null, and by convention should be null if the
  /// list is empty.
  List<String>? problemsAsJson;

  @override
  List<Expression> annotations;

  List<LibraryDependency> dependencies;

  /// References to nodes exported by `export` declarations that:
  /// - aren't ambiguous, or
  /// - aren't hidden by local declarations.
  final List<Reference> additionalExports = <Reference>[];

  @informative
  List<LibraryPart> parts;

  List<Typedef> _typedefs;
  List<Class> _classes;
  List<Extension> _extensions;
  List<Procedure> _procedures;
  List<Field> _fields;

  Library(this.importUri,
      {this.name,
      List<Expression>? annotations,
      List<LibraryDependency>? dependencies,
      List<LibraryPart>? parts,
      List<Typedef>? typedefs,
      List<Class>? classes,
      List<Extension>? extensions,
      List<Procedure>? procedures,
      List<Field>? fields,
      required this.fileUri,
      Reference? reference})
      // ignore: unnecessary_null_comparison
      : assert(fileUri != null),
        this.annotations = annotations ?? <Expression>[],
        this.dependencies = dependencies ?? <LibraryDependency>[],
        this.parts = parts ?? <LibraryPart>[],
        this._typedefs = typedefs ?? <Typedef>[],
        this._classes = classes ?? <Class>[],
        this._extensions = extensions ?? <Extension>[],
        this._procedures = procedures ?? <Procedure>[],
        this._fields = fields ?? <Field>[],
        super(reference) {
    setParents(this.dependencies, this);
    setParents(this.parts, this);
    setParents(this._typedefs, this);
    setParents(this._classes, this);
    setParents(this._extensions, this);
    setParents(this._procedures, this);
    setParents(this._fields, this);
  }

  List<Typedef> get typedefs => _typedefs;

  /// Internal. Should *ONLY* be used from within kernel.
  ///
  /// Used for adding typedefs when reading the dill file.
  void set typedefsInternal(List<Typedef> typedefs) {
    _typedefs = typedefs;
  }

  List<Class> get classes => _classes;

  /// Internal. Should *ONLY* be used from within kernel.
  ///
  /// Used for adding classes when reading the dill file.
  void set classesInternal(List<Class> classes) {
    _classes = classes;
  }

  List<Extension> get extensions => _extensions;

  /// Internal. Should *ONLY* be used from within kernel.
  ///
  /// Used for adding extensions when reading the dill file.
  void set extensionsInternal(List<Extension> extensions) {
    _extensions = extensions;
  }

  List<Procedure> get procedures => _procedures;

  /// Internal. Should *ONLY* be used from within kernel.
  ///
  /// Used for adding procedures when reading the dill file.
  void set proceduresInternal(List<Procedure> procedures) {
    _procedures = procedures;
  }

  List<Field> get fields => _fields;

  /// Internal. Should *ONLY* be used from within kernel.
  ///
  /// Used for adding fields when reading the dill file.
  void set fieldsInternal(List<Field> fields) {
    _fields = fields;
  }

  Nullability get nullable {
    return isNonNullableByDefault ? Nullability.nullable : Nullability.legacy;
  }

  Nullability get nonNullable {
    return isNonNullableByDefault
        ? Nullability.nonNullable
        : Nullability.legacy;
  }

  Nullability nullableIfTrue(bool isNullable) {
    if (isNonNullableByDefault) {
      return isNullable ? Nullability.nullable : Nullability.nonNullable;
    }
    return Nullability.legacy;
  }

  /// Returns the top-level fields and procedures defined in this library.
  ///
  /// This getter is for convenience, not efficiency.  Consider manually
  /// iterating the members to speed up code in production.
  Iterable<Member> get members =>
      <Iterable<Member>>[fields, procedures].expand((x) => x);

  @override
  void addAnnotation(Expression node) {
    node.parent = this;
    annotations.add(node);
  }

  void addClass(Class class_) {
    class_.parent = this;
    classes.add(class_);
  }

  void addExtension(Extension extension) {
    extension.parent = this;
    extensions.add(extension);
  }

  void addField(Field field) {
    field.parent = this;
    fields.add(field);
  }

  void addProcedure(Procedure procedure) {
    procedure.parent = this;
    procedures.add(procedure);
  }

  void addTypedef(Typedef typedef_) {
    typedef_.parent = this;
    typedefs.add(typedef_);
  }

  void computeCanonicalNames() {
    CanonicalName canonicalName = this.reference.canonicalName!;
    for (int i = 0; i < typedefs.length; ++i) {
      Typedef typedef_ = typedefs[i];
      canonicalName.getChildFromTypedef(typedef_).bindTo(typedef_.reference);
    }
    for (int i = 0; i < fields.length; ++i) {
      Field field = fields[i];
      canonicalName.getChildFromField(field).bindTo(field.getterReference);
      if (field.hasSetter) {
        canonicalName
            .getChildFromFieldSetter(field)
            .bindTo(field.setterReference!);
      }
    }
    for (int i = 0; i < procedures.length; ++i) {
      Procedure member = procedures[i];
      canonicalName.getChildFromProcedure(member).bindTo(member.reference);
    }
    for (int i = 0; i < classes.length; ++i) {
      Class class_ = classes[i];
      canonicalName.getChild(class_.name).bindTo(class_.reference);
      class_.computeCanonicalNames();
    }
    for (int i = 0; i < extensions.length; ++i) {
      Extension extension = extensions[i];
      canonicalName.getChild(extension.name).bindTo(extension.reference);
    }
  }

  /// This is an advanced feature. Use of this method should be coordinated
  /// with the kernel team.
  ///
  /// See [Component.relink] for a comprehensive description.
  ///
  /// Makes sure all references in named nodes in this library points to said
  /// named node.
  void relink() {
    _relinkNode();
    for (int i = 0; i < typedefs.length; ++i) {
      Typedef typedef_ = typedefs[i];
      typedef_._relinkNode();
    }
    for (int i = 0; i < fields.length; ++i) {
      Field field = fields[i];
      field._relinkNode();
    }
    for (int i = 0; i < procedures.length; ++i) {
      Procedure member = procedures[i];
      member._relinkNode();
    }
    for (int i = 0; i < classes.length; ++i) {
      Class class_ = classes[i];
      class_.relink();
    }
    for (int i = 0; i < extensions.length; ++i) {
      Extension extension = extensions[i];
      extension._relinkNode();
    }
  }

  void addDependency(LibraryDependency node) {
    dependencies.add(node..parent = this);
  }

  void addPart(LibraryPart node) {
    parts.add(node..parent = this);
  }

  @override
  R accept<R>(TreeVisitor<R> v) => v.visitLibrary(this);

  @override
  R accept1<R, A>(TreeVisitor1<R, A> v, A arg) => v.visitLibrary(this, arg);

  @override
  void visitChildren(Visitor v) {
    visitList(annotations, v);
    visitList(dependencies, v);
    visitList(parts, v);
    visitList(typedefs, v);
    visitList(classes, v);
    visitList(extensions, v);
    visitList(procedures, v);
    visitList(fields, v);
  }

  @override
  void transformChildren(Transformer v) {
    v.transformList(annotations, this);
    v.transformList(dependencies, this);
    v.transformList(parts, this);
    v.transformList(typedefs, this);
    v.transformList(classes, this);
    v.transformList(extensions, this);
    v.transformList(procedures, this);
    v.transformList(fields, this);
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    v.transformExpressionList(annotations, this);
    v.transformLibraryDependencyList(dependencies, this);
    v.transformLibraryPartList(parts, this);
    v.transformTypedefList(typedefs, this);
    v.transformClassList(classes, this);
    v.transformExtensionList(extensions, this);
    v.transformProcedureList(procedures, this);
    v.transformFieldList(fields, this);
  }

  static int _libraryIdCounter = 0;
  int _libraryId = ++_libraryIdCounter;
  int get libraryIdForTesting => _libraryId;

  @override
  int compareTo(Library other) => _libraryId - other._libraryId;

  /// Returns a possibly synthesized name for this library, consistent with
  /// the names across all [toString] calls.
  @override
  String toString() => libraryNameToString(this);

  @override
  void toTextInternal(AstPrinter printer) {
    printer.write(libraryNameToString(this));
  }

  Location? _getLocationInEnclosingFile(int offset) {
    return _getLocationInComponent(enclosingComponent, fileUri, offset);
  }

  String leakingDebugToString() => astToText.debugLibraryToString(this);
}

/// An import or export declaration in a library.
///
/// It can represent any of the following forms,
///
///     import <url>;
///     import <url> as <name>;
///     import <url> deferred as <name>;
///     export <url>;
///
/// optionally with metadata and [Combinators].
class LibraryDependency extends TreeNode implements Annotatable {
  int flags;

  @override
  final List<Expression> annotations;

  Reference importedLibraryReference;

  /// The name of the import prefix, if any, or `null` if this is not an import
  /// with a prefix.
  ///
  /// Must be non-null for deferred imports, and must be null for exports.
  String? name;

  final List<Combinator> combinators;

  LibraryDependency(int flags, List<Expression> annotations,
      Library importedLibrary, String name, List<Combinator> combinators)
      : this.byReference(
            flags, annotations, importedLibrary.reference, name, combinators);

  LibraryDependency.deferredImport(Library importedLibrary, String name,
      {List<Combinator>? combinators, List<Expression>? annotations})
      : this.byReference(DeferredFlag, annotations ?? <Expression>[],
            importedLibrary.reference, name, combinators ?? <Combinator>[]);

  LibraryDependency.import(Library importedLibrary,
      {String? name,
      List<Combinator>? combinators,
      List<Expression>? annotations})
      : this.byReference(0, annotations ?? <Expression>[],
            importedLibrary.reference, name, combinators ?? <Combinator>[]);

  LibraryDependency.export(Library importedLibrary,
      {List<Combinator>? combinators, List<Expression>? annotations})
      : this.byReference(ExportFlag, annotations ?? <Expression>[],
            importedLibrary.reference, null, combinators ?? <Combinator>[]);

  LibraryDependency.byReference(this.flags, this.annotations,
      this.importedLibraryReference, this.name, this.combinators) {
    setParents(annotations, this);
    setParents(combinators, this);
  }

  Library get enclosingLibrary => parent as Library;
  Library get targetLibrary => importedLibraryReference.asLibrary;

  static const int ExportFlag = 1 << 0;
  static const int DeferredFlag = 1 << 1;

  bool get isExport => flags & ExportFlag != 0;
  bool get isImport => !isExport;
  bool get isDeferred => flags & DeferredFlag != 0;

  @override
  void addAnnotation(Expression annotation) {
    annotations.add(annotation..parent = this);
  }

  @override
  R accept<R>(TreeVisitor<R> v) => v.visitLibraryDependency(this);

  @override
  R accept1<R, A>(TreeVisitor1<R, A> v, A arg) =>
      v.visitLibraryDependency(this, arg);

  @override
  void visitChildren(Visitor v) {
    visitList(annotations, v);
    visitList(combinators, v);
  }

  @override
  void transformChildren(Transformer v) {
    v.transformList(annotations, this);
    v.transformList(combinators, this);
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    v.transformExpressionList(annotations, this);
    v.transformCombinatorList(combinators, this);
  }

  @override
  String toString() {
    return "LibraryDependency(${toStringInternal()})";
  }

  @override
  void toTextInternal(AstPrinter printer) {
    // TODO(johnniwinther): Implement this.
  }
}

/// A part declaration in a library.
///
///     part <url>;
///
/// optionally with metadata.
class LibraryPart extends TreeNode implements Annotatable {
  @override
  final List<Expression> annotations;

  final String partUri;

  LibraryPart(this.annotations, this.partUri) {
    setParents(annotations, this);
  }

  @override
  void addAnnotation(Expression annotation) {
    annotations.add(annotation..parent = this);
  }

  @override
  R accept<R>(TreeVisitor<R> v) => v.visitLibraryPart(this);

  @override
  R accept1<R, A>(TreeVisitor1<R, A> v, A arg) => v.visitLibraryPart(this, arg);

  @override
  void visitChildren(Visitor v) {
    visitList(annotations, v);
  }

  @override
  void transformChildren(Transformer v) {
    v.transformList(annotations, this);
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    v.transformExpressionList(annotations, this);
  }

  @override
  String toString() {
    return "LibraryPart(${toStringInternal()})";
  }

  @override
  void toTextInternal(AstPrinter printer) {
    // TODO(johnniwinther): Implement this.
  }
}

/// A `show` or `hide` clause for an import or export.
class Combinator extends TreeNode {
  bool isShow;

  final List<String> names;

  LibraryDependency get dependency => parent as LibraryDependency;

  Combinator(this.isShow, this.names);
  Combinator.show(this.names) : isShow = true;
  Combinator.hide(this.names) : isShow = false;

  bool get isHide => !isShow;

  @override
  R accept<R>(TreeVisitor<R> v) => v.visitCombinator(this);

  @override
  R accept1<R, A>(TreeVisitor1<R, A> v, A arg) => v.visitCombinator(this, arg);

  @override
  void visitChildren(Visitor v) {}

  @override
  void transformChildren(Transformer v) {}

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {}

  @override
  String toString() {
    return "Combinator(${toStringInternal()})";
  }

  @override
  void toTextInternal(AstPrinter printer) {
    // TODO(johnniwinther): Implement this.
  }
}

/// Declaration of a type alias.
class Typedef extends NamedNode implements FileUriNode, Annotatable {
  /// The URI of the source file that contains the declaration of this typedef.
  @override
  Uri fileUri;

  @override
  List<Expression> annotations = const <Expression>[];

  String name;
  final List<TypeParameter> typeParameters;
  // TODO(johnniwinther): Make this non-nullable.
  DartType? type;

  // The following fields describe parameters of the underlying type when
  // that is a function type.  They are needed to keep such attributes as names
  // and annotations. When the underlying type is not a function type, they are
  // empty.
  final List<TypeParameter> typeParametersOfFunctionType;
  final List<VariableDeclaration> positionalParameters;
  final List<VariableDeclaration> namedParameters;

  Typedef(this.name, this.type,
      {Reference? reference,
      required this.fileUri,
      List<TypeParameter>? typeParameters,
      List<TypeParameter>? typeParametersOfFunctionType,
      List<VariableDeclaration>? positionalParameters,
      List<VariableDeclaration>? namedParameters})
      // ignore: unnecessary_null_comparison
      : assert(fileUri != null),
        this.typeParameters = typeParameters ?? <TypeParameter>[],
        this.typeParametersOfFunctionType =
            typeParametersOfFunctionType ?? <TypeParameter>[],
        this.positionalParameters =
            positionalParameters ?? <VariableDeclaration>[],
        this.namedParameters = namedParameters ?? <VariableDeclaration>[],
        super(reference) {
    setParents(this.typeParameters, this);
    setParents(this.typeParametersOfFunctionType, this);
    setParents(this.positionalParameters, this);
    setParents(this.namedParameters, this);
  }

  Library get enclosingLibrary => parent as Library;

  @override
  R accept<R>(TreeVisitor<R> v) => v.visitTypedef(this);

  @override
  R accept1<R, A>(TreeVisitor1<R, A> v, A arg) => v.visitTypedef(this, arg);

  @override
  void visitChildren(Visitor v) {
    visitList(annotations, v);
    visitList(typeParameters, v);
    type?.accept(v);
    visitList(typeParametersOfFunctionType, v);
    visitList(positionalParameters, v);
    visitList(namedParameters, v);
  }

  @override
  void transformChildren(Transformer v) {
    v.transformList(annotations, this);
    v.transformList(typeParameters, this);
    if (type != null) {
      type = v.visitDartType(type!);
    }
    v.transformList(typeParametersOfFunctionType, this);
    v.transformList(positionalParameters, this);
    v.transformList(namedParameters, this);
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    v.transformExpressionList(annotations, this);
    v.transformTypeParameterList(typeParameters, this);
    if (type != null) {
      DartType newType = v.visitDartType(type!, dummyDartType);
      if (identical(newType, dummyDartType)) {
        type = null;
      } else {
        type = newType;
      }
    }
    v.transformTypeParameterList(typeParametersOfFunctionType, this);
    v.transformVariableDeclarationList(positionalParameters, this);
    v.transformVariableDeclarationList(namedParameters, this);
  }

  @override
  void addAnnotation(Expression node) {
    if (annotations.isEmpty) {
      annotations = <Expression>[];
    }
    annotations.add(node);
    node.parent = this;
  }

  @override
  Location? _getLocationInEnclosingFile(int offset) {
    return _getLocationInComponent(enclosingComponent, fileUri, offset);
  }

  @override
  String toString() {
    return "Typedef(${toStringInternal()})";
  }

  @override
  void toTextInternal(AstPrinter printer) {
    printer.writeTypedefName(reference);
  }
}

/// List-wrapper that marks the parent-class as dirty if the list is modified.
///
/// The idea being, that for non-dirty classes (classes just loaded from dill)
/// the canonical names has already been calculated, and recalculating them is
/// not needed. If, however, we change anything, recalculation of the canonical
/// names can be needed.
class DirtifyingList<E> extends ListBase<E> {
  final Class dirtifyClass;
  final List<E> wrapped;

  DirtifyingList(this.dirtifyClass, this.wrapped);

  @override
  int get length {
    return wrapped.length;
  }

  @override
  void set length(int length) {
    dirtifyClass.dirty = true;
    wrapped.length = length;
  }

  @override
  E operator [](int index) {
    return wrapped[index];
  }

  @override
  void operator []=(int index, E value) {
    dirtifyClass.dirty = true;
    wrapped[index] = value;
  }
}

/// Declaration of a regular class or a mixin application.
///
/// Mixin applications may not contain fields or procedures, as they implicitly
/// use those from its mixed-in type.  However, the IR does not enforce this
/// rule directly, as doing so can obstruct transformations.  It is possible to
/// transform a mixin application to become a regular class, and vice versa.
class Class extends NamedNode implements Annotatable, FileUriNode {
  /// Start offset of the class in the source file it comes from.
  ///
  /// Note that this includes annotations if any.
  ///
  /// Valid values are from 0 and up, or -1 ([TreeNode.noOffset]) if the file
  /// start offset is not available (this is the default if none is specifically
  /// set).
  int startFileOffset = TreeNode.noOffset;

  /// End offset in the source file it comes from. Valid values are from 0 and
  /// up, or -1 ([TreeNode.noOffset]) if the file end offset is not available
  /// (this is the default if none is specifically set).
  int fileEndOffset = TreeNode.noOffset;

  /// List of metadata annotations on the class.
  ///
  /// This defaults to an immutable empty list. Use [addAnnotation] to add
  /// annotations if needed.
  @override
  List<Expression> annotations = const <Expression>[];

  /// Name of the class.
  ///
  /// Must be non-null and must be unique within the library.
  ///
  /// The name may contain characters that are not valid in a Dart identifier,
  /// in particular, the symbol '&' is used in class names generated for mixin
  /// applications.
  String name;

  // Must match serialized bit positions.
  static const int FlagAbstract = 1 << 0;
  static const int FlagEnum = 1 << 1;
  static const int FlagAnonymousMixin = 1 << 2;
  static const int FlagEliminatedMixin = 1 << 3;
  static const int FlagMixinDeclaration = 1 << 4;
  static const int FlagHasConstConstructor = 1 << 5;

  int flags = 0;

  bool get isAbstract => flags & FlagAbstract != 0;

  void set isAbstract(bool value) {
    flags = value ? (flags | FlagAbstract) : (flags & ~FlagAbstract);
  }

  /// Whether this class is an enum.
  bool get isEnum => flags & FlagEnum != 0;

  void set isEnum(bool value) {
    flags = value ? (flags | FlagEnum) : (flags & ~FlagEnum);
  }

  /// Whether this class is a synthetic implementation created for each
  /// mixed-in class. For example the following code:
  /// class Z extends A with B, C, D {}
  /// class A {}
  /// class B {}
  /// class C {}
  /// class D {}
  /// ...creates:
  /// abstract class _Z&A&B extends A mixedIn B {}
  /// abstract class _Z&A&B&C extends A&B mixedIn C {}
  /// abstract class _Z&A&B&C&D extends A&B&C mixedIn D {}
  /// class Z extends _Z&A&B&C&D {}
  /// All X&Y classes are marked as synthetic.
  bool get isAnonymousMixin => flags & FlagAnonymousMixin != 0;

  void set isAnonymousMixin(bool value) {
    flags =
        value ? (flags | FlagAnonymousMixin) : (flags & ~FlagAnonymousMixin);
  }

  /// Whether this class was transformed from a mixin application.
  /// In such case, its mixed-in type was pulled into the end of implemented
  /// types list.
  bool get isEliminatedMixin => flags & FlagEliminatedMixin != 0;

  void set isEliminatedMixin(bool value) {
    flags =
        value ? (flags | FlagEliminatedMixin) : (flags & ~FlagEliminatedMixin);
  }

  /// True if this class was a mixin declaration in Dart.
  ///
  /// Mixins are declared in Dart with the `mixin` keyword.  They are compiled
  /// to Kernel classes.
  bool get isMixinDeclaration => flags & FlagMixinDeclaration != 0;

  void set isMixinDeclaration(bool value) {
    flags = value
        ? (flags | FlagMixinDeclaration)
        : (flags & ~FlagMixinDeclaration);
  }

  /// True if this class declares one or more constant constructors.
  bool get hasConstConstructor => flags & FlagHasConstConstructor != 0;

  void set hasConstConstructor(bool value) {
    flags = value
        ? (flags | FlagHasConstConstructor)
        : (flags & ~FlagHasConstConstructor);
  }

  List<Supertype> superclassConstraints() {
    List<Supertype> constraints = <Supertype>[];

    // Not a mixin declaration.
    if (!isMixinDeclaration) return constraints;

    // Otherwise we have a left-linear binary tree (subtrees are supertype and
    // mixedInType) of constraints, where all the interior nodes are anonymous
    // mixin applications.
    Supertype? current = supertype;
    while (current != null && current.classNode.isAnonymousMixin) {
      Class currentClass = current.classNode;
      assert(currentClass.implementedTypes.length == 2);
      Substitution substitution = Substitution.fromSupertype(current);
      constraints.add(
          substitution.substituteSupertype(currentClass.implementedTypes[1]));
      current =
          substitution.substituteSupertype(currentClass.implementedTypes[0]);
    }
    return constraints..add(current!);
  }

  /// The URI of the source file this class was loaded from.
  @override
  Uri fileUri;

  final List<TypeParameter> typeParameters;

  /// The immediate super type, or `null` if this is the root class.
  Supertype? supertype;

  /// The mixed-in type if this is a mixin application, otherwise `null`.
  Supertype? mixedInType;

  /// The types from the `implements` clause.
  List<Supertype> implementedTypes;

  /// Internal. Should *ONLY* be used from within kernel.
  ///
  /// If non-null, the function that will have to be called to fill-out the
  /// content of this class. Note that this should not be called directly
  /// though.
  void Function()? lazyBuilder;

  /// Makes sure the class is loaded, i.e. the fields, procedures etc have been
  /// loaded from the dill. Generally, one should not need to call this as it is
  /// done automatically when accessing the lists.
  void ensureLoaded() {
    void Function()? lazyBuilderLocal = lazyBuilder;
    if (lazyBuilderLocal != null) {
      lazyBuilder = null;
      lazyBuilderLocal();
    }
  }

  List<Field> _fieldsInternal;
  DirtifyingList<Field>? _fieldsView;

  /// Fields declared in the class.
  ///
  /// For mixin applications this should be empty.
  List<Field> get fields {
    ensureLoaded();
    // If already dirty the caller just might as well add stuff directly too.
    if (dirty) return _fieldsInternal;
    return _fieldsView ??= new DirtifyingList(this, _fieldsInternal);
  }

  /// Internal. Should *ONLY* be used from within kernel.
  ///
  /// Used for adding fields when reading the dill file.
  void set fieldsInternal(List<Field> fields) {
    _fieldsInternal = fields;
    _fieldsView = null;
  }

  List<Constructor> _constructorsInternal;
  DirtifyingList<Constructor>? _constructorsView;

  /// Constructors declared in the class.
  List<Constructor> get constructors {
    ensureLoaded();
    // If already dirty the caller just might as well add stuff directly too.
    if (dirty) return _constructorsInternal;
    return _constructorsView ??=
        new DirtifyingList(this, _constructorsInternal);
  }

  /// Internal. Should *ONLY* be used from within kernel.
  ///
  /// Used for adding constructors when reading the dill file.
  void set constructorsInternal(List<Constructor> constructors) {
    _constructorsInternal = constructors;
    _constructorsView = null;
  }

  List<Procedure> _proceduresInternal;
  DirtifyingList<Procedure>? _proceduresView;

  /// Procedures declared in the class.
  ///
  /// For mixin applications this should only contain forwarding stubs.
  List<Procedure> get procedures {
    ensureLoaded();
    // If already dirty the caller just might as well add stuff directly too.
    if (dirty) return _proceduresInternal;
    return _proceduresView ??= new DirtifyingList(this, _proceduresInternal);
  }

  /// Internal. Should *ONLY* be used from within kernel.
  ///
  /// Used for adding procedures when reading the dill file.
  void set proceduresInternal(List<Procedure> procedures) {
    _proceduresInternal = procedures;
    _proceduresView = null;
  }

  List<RedirectingFactoryConstructor> _redirectingFactoryConstructorsInternal;
  DirtifyingList<RedirectingFactoryConstructor>?
      _redirectingFactoryConstructorsView;

  /// Redirecting factory constructors declared in the class.
  ///
  /// For mixin applications this should be empty.
  List<RedirectingFactoryConstructor> get redirectingFactoryConstructors {
    ensureLoaded();
    // If already dirty the caller just might as well add stuff directly too.
    if (dirty) return _redirectingFactoryConstructorsInternal;
    return _redirectingFactoryConstructorsView ??=
        new DirtifyingList(this, _redirectingFactoryConstructorsInternal);
  }

  /// Internal. Should *ONLY* be used from within kernel.
  ///
  /// Used for adding redirecting factory constructor when reading the dill
  /// file.
  void set redirectingFactoryConstructorsInternal(
      List<RedirectingFactoryConstructor> redirectingFactoryConstructors) {
    _redirectingFactoryConstructorsInternal = redirectingFactoryConstructors;
    _redirectingFactoryConstructorsView = null;
  }

  Class(
      {required this.name,
      bool isAbstract: false,
      bool isAnonymousMixin: false,
      this.supertype,
      this.mixedInType,
      List<TypeParameter>? typeParameters,
      List<Supertype>? implementedTypes,
      List<Constructor>? constructors,
      List<Procedure>? procedures,
      List<Field>? fields,
      List<RedirectingFactoryConstructor>? redirectingFactoryConstructors,
      required this.fileUri,
      Reference? reference})
      // ignore: unnecessary_null_comparison
      : assert(name != null),
        // ignore: unnecessary_null_comparison
        assert(fileUri != null),
        this.typeParameters = typeParameters ?? <TypeParameter>[],
        this.implementedTypes = implementedTypes ?? <Supertype>[],
        this._fieldsInternal = fields ?? <Field>[],
        this._constructorsInternal = constructors ?? <Constructor>[],
        this._proceduresInternal = procedures ?? <Procedure>[],
        this._redirectingFactoryConstructorsInternal =
            redirectingFactoryConstructors ?? <RedirectingFactoryConstructor>[],
        super(reference) {
    setParents(this.typeParameters, this);
    setParents(this._constructorsInternal, this);
    setParents(this._proceduresInternal, this);
    setParents(this._fieldsInternal, this);
    setParents(this._redirectingFactoryConstructorsInternal, this);
    this.isAbstract = isAbstract;
    this.isAnonymousMixin = isAnonymousMixin;
  }

  void computeCanonicalNames() {
    CanonicalName canonicalName = this.reference.canonicalName!;
    if (!dirty) return;
    for (int i = 0; i < fields.length; ++i) {
      Field member = fields[i];
      canonicalName.getChildFromField(member).bindTo(member.getterReference);
      if (member.hasSetter) {
        canonicalName
            .getChildFromFieldSetter(member)
            .bindTo(member.setterReference!);
      }
    }
    for (int i = 0; i < procedures.length; ++i) {
      Procedure member = procedures[i];
      canonicalName.getChildFromProcedure(member).bindTo(member.reference);
    }
    for (int i = 0; i < constructors.length; ++i) {
      Constructor member = constructors[i];
      canonicalName.getChildFromConstructor(member).bindTo(member.reference);
    }
    for (int i = 0; i < redirectingFactoryConstructors.length; ++i) {
      RedirectingFactoryConstructor member = redirectingFactoryConstructors[i];
      canonicalName
          .getChildFromRedirectingFactoryConstructor(member)
          .bindTo(member.reference);
    }
    dirty = false;
  }

  /// This is an advanced feature. Use of this method should be coordinated
  /// with the kernel team.
  ///
  /// See [Component.relink] for a comprehensive description.
  ///
  /// Makes sure all references in named nodes in this class points to said
  /// named node.
  void relink() {
    this.reference.node = this;
    for (int i = 0; i < fields.length; ++i) {
      Field member = fields[i];
      member._relinkNode();
    }
    for (int i = 0; i < procedures.length; ++i) {
      Procedure member = procedures[i];
      member._relinkNode();
    }
    for (int i = 0; i < constructors.length; ++i) {
      Constructor member = constructors[i];
      member._relinkNode();
    }
    for (int i = 0; i < redirectingFactoryConstructors.length; ++i) {
      RedirectingFactoryConstructor member = redirectingFactoryConstructors[i];
      member._relinkNode();
    }
    dirty = false;
  }

  /// The immediate super class, or `null` if this is the root class.
  Class? get superclass => supertype?.classNode;

  /// The mixed-in class if this is a mixin application, otherwise `null`.
  ///
  /// Note that this may itself be a mixin application.  Use [mixin] to get the
  /// class that has the fields and procedures.
  Class? get mixedInClass => mixedInType?.classNode;

  /// The class that declares the field and procedures of this class.
  Class get mixin => mixedInClass?.mixin ?? this;

  bool get isMixinApplication => mixedInType != null;

  String get demangledName {
    if (isAnonymousMixin) return nameAsMixinApplication;
    assert(!name.contains('&'));
    return name;
  }

  String get nameAsMixinApplication {
    assert(isAnonymousMixin);
    return demangleMixinApplicationName(name);
  }

  String get nameAsMixinApplicationSubclass {
    assert(isAnonymousMixin);
    return demangleMixinApplicationSubclassName(name);
  }

  /// Members declared in this class.
  ///
  /// This getter is for convenience, not efficiency.  Consider manually
  /// iterating the members to speed up code in production.
  Iterable<Member> get members => <Iterable<Member>>[
        fields,
        constructors,
        procedures,
        redirectingFactoryConstructors
      ].expand((x) => x);

  /// The immediately extended, mixed-in, and implemented types.
  ///
  /// This getter is for convenience, not efficiency.  Consider manually
  /// iterating the super types to speed up code in production.
  Iterable<Supertype> get supers => <Iterable<Supertype>>[
        supertype == null ? const [] : [supertype!],
        mixedInType == null ? const [] : [mixedInType!],
        implementedTypes
      ].expand((x) => x);

  /// The library containing this class.
  Library get enclosingLibrary => parent as Library;

  /// Internal. Should *ONLY* be used from within kernel.
  ///
  /// If true we have to compute canonical names for all children of this class.
  /// if false we can skip it.
  bool dirty = true;

  /// Adds a constructor to this class.
  void addConstructor(Constructor constructor) {
    dirty = true;
    constructor.parent = this;
    _constructorsInternal.add(constructor);
  }

  /// Adds a procedure to this class.
  void addProcedure(Procedure procedure) {
    dirty = true;
    procedure.parent = this;
    _proceduresInternal.add(procedure);
  }

  /// Adds a field to this class.
  void addField(Field field) {
    dirty = true;
    field.parent = this;
    _fieldsInternal.add(field);
  }

  /// Adds a field to this class.
  void addRedirectingFactoryConstructor(
      RedirectingFactoryConstructor redirectingFactoryConstructor) {
    dirty = true;
    redirectingFactoryConstructor.parent = this;
    _redirectingFactoryConstructorsInternal.add(redirectingFactoryConstructor);
  }

  @override
  void addAnnotation(Expression node) {
    if (annotations.isEmpty) {
      annotations = <Expression>[];
    }
    annotations.add(node);
    node.parent = this;
  }

  @override
  R accept<R>(TreeVisitor<R> v) => v.visitClass(this);

  @override
  R accept1<R, A>(TreeVisitor1<R, A> v, A arg) => v.visitClass(this, arg);

  R acceptReference<R>(Visitor<R> v) => v.visitClassReference(this);

  Supertype get asRawSupertype {
    return new Supertype(this,
        new List<DartType>.filled(typeParameters.length, const DynamicType()));
  }

  Supertype get asThisSupertype {
    return new Supertype(
        this, getAsTypeArguments(typeParameters, this.enclosingLibrary));
  }

  /// Returns the type of `this` for the class using [coreTypes] for caching.
  InterfaceType getThisType(CoreTypes coreTypes, Nullability nullability) {
    return coreTypes.thisInterfaceType(this, nullability);
  }

  @override
  String toString() => 'Class(${toStringInternal()})';

  @override
  void toTextInternal(AstPrinter printer) {
    printer.writeClassName(reference);
  }

  @override
  void visitChildren(Visitor v) {
    visitList(annotations, v);
    visitList(typeParameters, v);
    supertype?.accept(v);
    mixedInType?.accept(v);
    visitList(implementedTypes, v);
    visitList(constructors, v);
    visitList(procedures, v);
    visitList(fields, v);
    visitList(redirectingFactoryConstructors, v);
  }

  @override
  void transformChildren(Transformer v) {
    v.transformList(annotations, this);
    v.transformList(typeParameters, this);
    if (supertype != null) {
      supertype = v.visitSupertype(supertype!);
    }
    if (mixedInType != null) {
      mixedInType = v.visitSupertype(mixedInType!);
    }
    v.transformSupertypeList(implementedTypes);
    v.transformList(constructors, this);
    v.transformList(procedures, this);
    v.transformList(fields, this);
    v.transformList(redirectingFactoryConstructors, this);
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    v.transformExpressionList(annotations, this);
    v.transformTypeParameterList(typeParameters, this);
    if (supertype != null) {
      Supertype newSupertype = v.visitSupertype(supertype!, dummySupertype);
      if (identical(newSupertype, dummySupertype)) {
        supertype = null;
      } else {
        supertype = newSupertype;
      }
    }
    if (mixedInType != null) {
      Supertype newMixedInType = v.visitSupertype(mixedInType!, dummySupertype);
      if (identical(newMixedInType, dummySupertype)) {
        mixedInType = null;
      } else {
        mixedInType = newMixedInType;
      }
    }
    v.transformSupertypeList(implementedTypes);
    v.transformConstructorList(constructors, this);
    v.transformProcedureList(procedures, this);
    v.transformFieldList(fields, this);
    v.transformRedirectingFactoryConstructorList(
        redirectingFactoryConstructors, this);
  }

  @override
  Location? _getLocationInEnclosingFile(int offset) {
    return _getLocationInComponent(enclosingComponent, fileUri, offset);
  }
}

/// Declaration of an extension.
///
/// The members are converted into top-level procedures and only accessible
/// by reference in the [Extension] node.
class Extension extends NamedNode implements Annotatable, FileUriNode {
  /// Name of the extension.
  ///
  /// If unnamed, the extension will be given a synthesized name by the
  /// front end.
  String name;

  /// The URI of the source file this class was loaded from.
  Uri fileUri;

  /// Type parameters declared on the extension.
  final List<TypeParameter> typeParameters;

  /// The type in the 'on clause' of the extension declaration.
  ///
  /// For instance A in:
  ///
  ///   class A {}
  ///   extension B on A {}
  ///
  late DartType onType;

  /// The members declared by the extension.
  ///
  /// The members are converted into top-level members and only accessible
  /// by reference through [ExtensionMemberDescriptor].
  List<ExtensionMemberDescriptor> members;

  @override
  List<Expression> annotations = const <Expression>[];

  // Must match serialized bit positions.
  static const int FlagExtensionTypeDeclaration = 1 << 0;

  int flags = 0;

  @override
  void addAnnotation(Expression node) {
    if (annotations.isEmpty) {
      annotations = <Expression>[];
    }
    annotations.add(node);
    node.parent = this;
  }

  Extension(
      {required this.name,
      List<TypeParameter>? typeParameters,
      DartType? onType,
      List<ExtensionMemberDescriptor>? members,
      required this.fileUri,
      Reference? reference})
      // ignore: unnecessary_null_comparison
      : assert(name != null),
        // ignore: unnecessary_null_comparison
        assert(fileUri != null),
        this.typeParameters = typeParameters ?? <TypeParameter>[],
        this.members = members ?? <ExtensionMemberDescriptor>[],
        super(reference) {
    setParents(this.typeParameters, this);
    if (onType != null) {
      this.onType = onType;
    }
  }

  Library get enclosingLibrary => parent as Library;

  bool get isExtensionTypeDeclaration {
    return flags & FlagExtensionTypeDeclaration != 0;
  }

  void set isExtensionTypeDeclaration(bool value) {
    flags = value
        ? (flags | FlagExtensionTypeDeclaration)
        : (flags & ~FlagExtensionTypeDeclaration);
  }

  @override
  R accept<R>(TreeVisitor<R> v) => v.visitExtension(this);

  @override
  R accept1<R, A>(TreeVisitor1<R, A> v, A arg) => v.visitExtension(this, arg);

  R acceptReference<R>(Visitor<R> v) => v.visitExtensionReference(this);

  @override
  void visitChildren(Visitor v) {
    visitList(typeParameters, v);
    onType.accept(v);
  }

  @override
  void transformChildren(Transformer v) {
    v.transformList(typeParameters, this);
    // ignore: unnecessary_null_comparison
    if (onType != null) {
      onType = v.visitDartType(onType);
    }
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    v.transformTypeParameterList(typeParameters, this);
    // ignore: unnecessary_null_comparison
    if (onType != null) {
      onType = v.visitDartType(onType, cannotRemoveSentinel);
    }
  }

  @override
  Location? _getLocationInEnclosingFile(int offset) {
    return _getLocationInComponent(enclosingComponent, fileUri, offset);
  }

  @override
  String toString() {
    return "Extension(${toStringInternal()})";
  }

  @override
  void toTextInternal(AstPrinter printer) {
    printer.writeExtensionName(reference);
  }
}

enum ExtensionMemberKind {
  Field,
  Method,
  Getter,
  Setter,
  Operator,
  TearOff,
}

/// Information about an member declaration in an extension.
class ExtensionMemberDescriptor {
  static const int FlagStatic = 1 << 0; // Must match serialized bit positions.

  /// The name of the extension member.
  ///
  /// The name of the generated top-level member is mangled to ensure
  /// uniqueness. This name is used to lookup an extension method the
  /// extension itself.
  Name name;

  /// [ExtensionMemberKind] kind of the original member.
  ///
  /// An extension method is converted into a regular top-level method. For
  /// instance:
  ///
  ///     class A {
  ///       var foo;
  ///     }
  ///     extension B on A {
  ///       get bar => this.foo;
  ///     }
  ///
  /// will be converted into
  ///
  ///     class A {}
  ///     B|get#bar(A #this) => #this.foo;
  ///
  /// where `B|get#bar` is the synthesized name of the top-level method and
  /// `#this` is the synthesized parameter that holds represents `this`.
  ///
  ExtensionMemberKind kind;

  int flags = 0;

  /// Reference to the top-level member created for the extension method.
  final Reference member;

  ExtensionMemberDescriptor(
      {required this.name,
      required this.kind,
      bool isStatic: false,
      required this.member}) {
    this.isStatic = isStatic;
  }

  /// Return `true` if the extension method was declared as `static`.
  bool get isStatic => flags & FlagStatic != 0;

  void set isStatic(bool value) {
    flags = value ? (flags | FlagStatic) : (flags & ~FlagStatic);
  }

  @override
  String toString() {
    return 'ExtensionMemberDescriptor($name,$kind,'
        '${member.toStringInternal()},isStatic=${isStatic})';
  }
}

// ------------------------------------------------------------------------
//                            MEMBERS
// ------------------------------------------------------------------------

abstract class Member extends NamedNode implements Annotatable, FileUriNode {
  /// End offset in the source file it comes from.
  ///
  /// Valid values are from 0 and up, or -1 ([TreeNode.noOffset]) if the file
  /// end offset is not available (this is the default if none is specifically
  /// set).
  int fileEndOffset = TreeNode.noOffset;

  /// List of metadata annotations on the member.
  ///
  /// This defaults to an immutable empty list. Use [addAnnotation] to add
  /// annotations if needed.
  @override
  List<Expression> annotations = const <Expression>[];

  Name name;

  /// The URI of the source file this member was loaded from.
  @override
  Uri fileUri;

  /// Flags summarizing the kinds of AST nodes contained in this member, for
  /// speeding up transformations that only affect certain types of nodes.
  ///
  /// See [TransformerFlag] for the meaning of each bit.
  ///
  /// These should not be used for any purpose other than skipping certain
  /// members if it can be determined that no work is needed in there.
  ///
  /// It is valid for these flags to be false positives in rare cases, so
  /// transformers must tolerate the case where a flag is spuriously set.
  ///
  /// This value is not serialized; it is populated by the frontend and the
  /// deserializer.
  //
  // TODO(asgerf): It might be worthwhile to put this on classes as well.
  int transformerFlags = 0;

  Member(this.name, this.fileUri, Reference? reference)
      // ignore: unnecessary_null_comparison
      : assert(name != null),
        // ignore: unnecessary_null_comparison
        assert(fileUri != null),
        super(reference);

  Class? get enclosingClass => parent is Class ? parent as Class : null;
  Library get enclosingLibrary =>
      (parent is Class ? parent!.parent : parent) as Library;

  @override
  R accept<R>(MemberVisitor<R> v);

  @override
  R accept1<R, A>(MemberVisitor1<R, A> v, A arg);

  R acceptReference<R>(MemberReferenceVisitor<R> v);

  /// Returns true if this is an abstract procedure.
  bool get isAbstract => false;

  /// Returns true if the member has the 'const' modifier.
  bool get isConst;

  /// True if this is a field or non-setter procedure.
  ///
  /// Note that operators and factories return `true`, even though there are
  /// normally no calls to their getter.
  bool get hasGetter;

  /// True if this is a setter or a mutable field.
  bool get hasSetter;

  /// True if this is a non-static field or procedure.
  bool get isInstanceMember;

  /// True if the member has the `external` modifier, implying that the
  /// implementation is provided by the backend, and is not necessarily written
  /// in Dart.
  ///
  /// Members can have this modifier independently of whether the enclosing
  /// library is external.
  bool get isExternal;
  void set isExternal(bool value);

  /// If `true` this member is compiled from a member declared in an extension
  /// declaration.
  ///
  /// For instance `field`, `method1` and `method2` in:
  ///
  ///     extension A on B {
  ///       static var field;
  ///       B method1() => this;
  ///       static B method2() => new B();
  ///     }
  ///
  bool get isExtensionMember;

  /// If `true` this member is defined in a library for which non-nullable by
  /// default is enabled.
  bool get isNonNullableByDefault;
  void set isNonNullableByDefault(bool value);

  /// The function signature and body of the procedure or constructor, or `null`
  /// if this is a field.
  FunctionNode? get function => null;

  /// Returns a possibly synthesized name for this member, consistent with
  /// the names used across all [toString] calls.
  @override
  String toString() => toStringInternal();

  @override
  void toTextInternal(AstPrinter printer) {
    printer.writeMemberName(reference);
  }

  @override
  void addAnnotation(Expression node) {
    if (annotations.isEmpty) {
      annotations = <Expression>[];
    }
    annotations.add(node);
    node.parent = this;
  }

  DartType get getterType;
  DartType get setterType;

  bool get containsSuperCalls {
    return transformerFlags & TransformerFlag.superCalls != 0;
  }

  /// If this member is a member signature, [memberSignatureOrigin] is one of
  /// the non-member signature members from which it was created.
  Member? get memberSignatureOrigin => null;
}

/// A field declaration.
///
/// The implied getter and setter for the field are not represented explicitly,
/// but can be made explicit if needed.
class Field extends Member {
  DartType type; // Not null. Defaults to DynamicType.
  int flags = 0;
  Expression? initializer; // May be null.
  final Reference? setterReference;

  @override
  @Deprecated("Use the specific getterReference/setterReference instead")
  Reference get reference => super.reference;

  Reference get getterReference => super.reference;

  Field.mutable(Name name,
      {this.type: const DynamicType(),
      this.initializer,
      bool isCovariant: false,
      bool isFinal: false,
      bool isStatic: false,
      bool isLate: false,
      int transformerFlags: 0,
      required Uri fileUri,
      Reference? getterReference,
      Reference? setterReference})
      : this.setterReference = setterReference ?? new Reference(),
        super(name, fileUri, getterReference) {
    this.setterReference!.node = this;
    // ignore: unnecessary_null_comparison
    assert(type != null);
    initializer?.parent = this;
    this.isCovariant = isCovariant;
    this.isFinal = isFinal;
    this.isStatic = isStatic;
    this.isLate = isLate;
    this.transformerFlags = transformerFlags;
  }

  Field.immutable(Name name,
      {this.type: const DynamicType(),
      this.initializer,
      bool isCovariant: false,
      bool isFinal: false,
      bool isConst: false,
      bool isStatic: false,
      bool isLate: false,
      int transformerFlags: 0,
      required Uri fileUri,
      Reference? getterReference})
      : this.setterReference = null,
        super(name, fileUri, getterReference) {
    // ignore: unnecessary_null_comparison
    assert(type != null);
    initializer?.parent = this;
    this.isCovariant = isCovariant;
    this.isFinal = isFinal;
    this.isConst = isConst;
    this.isStatic = isStatic;
    this.isLate = isLate;
    this.transformerFlags = transformerFlags;
  }

  @override
  void _relinkNode() {
    super._relinkNode();
    if (hasSetter) {
      this.setterReference!.node = this;
    }
  }

  static const int FlagFinal = 1 << 0; // Must match serialized bit positions.
  static const int FlagConst = 1 << 1;
  static const int FlagStatic = 1 << 2;
  static const int FlagCovariant = 1 << 3;
  static const int FlagGenericCovariantImpl = 1 << 4;
  static const int FlagLate = 1 << 5;
  static const int FlagExtensionMember = 1 << 6;
  static const int FlagNonNullableByDefault = 1 << 7;
  static const int FlagInternalImplementation = 1 << 8;

  /// Whether the field is declared with the `covariant` keyword.
  bool get isCovariant => flags & FlagCovariant != 0;

  bool get isFinal => flags & FlagFinal != 0;

  @override
  bool get isConst => flags & FlagConst != 0;

  bool get isStatic => flags & FlagStatic != 0;

  @override
  bool get isExtensionMember => flags & FlagExtensionMember != 0;

  /// Indicates whether the implicit setter associated with this field needs to
  /// contain a runtime type check to deal with generic covariance.
  ///
  /// When `true`, runtime checks may need to be performed; see
  /// [DispatchCategory] for details.
  bool get isGenericCovariantImpl => flags & FlagGenericCovariantImpl != 0;

  /// Whether the field is declared with the `late` keyword.
  bool get isLate => flags & FlagLate != 0;

  // If `true` this field is not part of the interface but only part of the
  // class members.
  //
  // This is `true` for instance for synthesized fields added for the late
  // lowering.
  bool get isInternalImplementation => flags & FlagInternalImplementation != 0;

  void set isCovariant(bool value) {
    flags = value ? (flags | FlagCovariant) : (flags & ~FlagCovariant);
  }

  void set isFinal(bool value) {
    flags = value ? (flags | FlagFinal) : (flags & ~FlagFinal);
  }

  void set isConst(bool value) {
    flags = value ? (flags | FlagConst) : (flags & ~FlagConst);
  }

  void set isStatic(bool value) {
    flags = value ? (flags | FlagStatic) : (flags & ~FlagStatic);
  }

  void set isExtensionMember(bool value) {
    flags =
        value ? (flags | FlagExtensionMember) : (flags & ~FlagExtensionMember);
  }

  void set isGenericCovariantImpl(bool value) {
    flags = value
        ? (flags | FlagGenericCovariantImpl)
        : (flags & ~FlagGenericCovariantImpl);
  }

  void set isLate(bool value) {
    flags = value ? (flags | FlagLate) : (flags & ~FlagLate);
  }

  void set isInternalImplementation(bool value) {
    flags = value
        ? (flags | FlagInternalImplementation)
        : (flags & ~FlagInternalImplementation);
  }

  @override
  bool get isInstanceMember => !isStatic;

  @override
  bool get hasGetter => true;

  @override
  bool get hasSetter => setterReference != null;

  @override
  bool get isExternal => false;

  @override
  void set isExternal(bool value) {
    if (value) throw 'Fields cannot be external';
  }

  @override
  bool get isNonNullableByDefault => flags & FlagNonNullableByDefault != 0;

  @override
  void set isNonNullableByDefault(bool value) {
    flags = value
        ? (flags | FlagNonNullableByDefault)
        : (flags & ~FlagNonNullableByDefault);
  }

  @override
  R accept<R>(MemberVisitor<R> v) => v.visitField(this);

  @override
  R accept1<R, A>(MemberVisitor1<R, A> v, A arg) => v.visitField(this, arg);

  @override
  R acceptReference<R>(MemberReferenceVisitor<R> v) =>
      v.visitFieldReference(this);

  @override
  void visitChildren(Visitor v) {
    visitList(annotations, v);
    type.accept(v);
    name.accept(v);
    initializer?.accept(v);
  }

  @override
  void transformChildren(Transformer v) {
    type = v.visitDartType(type);
    v.transformList(annotations, this);
    if (initializer != null) {
      initializer = v.transform(initializer!);
      initializer?.parent = this;
    }
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    type = v.visitDartType(type, null);
    v.transformExpressionList(annotations, this);
    if (initializer != null) {
      initializer = v.transformOrRemoveExpression(initializer!);
      initializer?.parent = this;
    }
  }

  @override
  DartType get getterType => type;

  @override
  DartType get setterType => hasSetter ? type : const NeverType.nonNullable();

  @override
  Location? _getLocationInEnclosingFile(int offset) {
    return _getLocationInComponent(enclosingComponent, fileUri, offset);
  }

  @override
  void toTextInternal(AstPrinter printer) {
    printer.writeMemberName(getterReference);
  }
}

/// A generative constructor, possibly redirecting.
///
/// Note that factory constructors are treated as [Procedure]s.
///
/// Constructors do not take type parameters.  Type arguments from a constructor
/// invocation should be matched with the type parameters declared in the class.
///
/// For unnamed constructors, the name is an empty string (in a [Name]).
class Constructor extends Member {
  /// Start offset of the constructor in the source file it comes from.
  ///
  /// Note that this includes annotations if any.
  ///
  /// Valid values are from 0 and up, or -1 ([TreeNode.noOffset]) if the file
  /// start offset is not available (this is the default if none is specifically
  /// set).
  int startFileOffset = TreeNode.noOffset;

  int flags = 0;

  @override
  FunctionNode function;

  List<Initializer> initializers;

  Constructor(this.function,
      {required Name name,
      bool isConst: false,
      bool isExternal: false,
      bool isSynthetic: false,
      List<Initializer>? initializers,
      int transformerFlags: 0,
      required Uri fileUri,
      Reference? reference})
      : this.initializers = initializers ?? <Initializer>[],
        // ignore: unnecessary_null_comparison
        assert(function != null),
        super(name, fileUri, reference) {
    function.parent = this;
    setParents(this.initializers, this);
    this.isConst = isConst;
    this.isExternal = isExternal;
    this.isSynthetic = isSynthetic;
    this.transformerFlags = transformerFlags;
  }

  @override
  Class get enclosingClass => parent as Class;

  static const int FlagConst = 1 << 0; // Must match serialized bit positions.
  static const int FlagExternal = 1 << 1;
  static const int FlagSynthetic = 1 << 2;
  static const int FlagNonNullableByDefault = 1 << 3;

  @override
  bool get isConst => flags & FlagConst != 0;

  @override
  bool get isExternal => flags & FlagExternal != 0;

  /// True if this is a synthetic constructor inserted in a class that
  /// does not otherwise declare any constructors.
  bool get isSynthetic => flags & FlagSynthetic != 0;

  void set isConst(bool value) {
    flags = value ? (flags | FlagConst) : (flags & ~FlagConst);
  }

  @override
  void set isExternal(bool value) {
    flags = value ? (flags | FlagExternal) : (flags & ~FlagExternal);
  }

  void set isSynthetic(bool value) {
    flags = value ? (flags | FlagSynthetic) : (flags & ~FlagSynthetic);
  }

  @override
  bool get isInstanceMember => false;

  @override
  bool get hasGetter => false;

  @override
  bool get hasSetter => false;

  @override
  bool get isExtensionMember => false;

  @override
  bool get isNonNullableByDefault => flags & FlagNonNullableByDefault != 0;

  @override
  void set isNonNullableByDefault(bool value) {
    flags = value
        ? (flags | FlagNonNullableByDefault)
        : (flags & ~FlagNonNullableByDefault);
  }

  @override
  R accept<R>(MemberVisitor<R> v) => v.visitConstructor(this);

  @override
  R accept1<R, A>(MemberVisitor1<R, A> v, A arg) =>
      v.visitConstructor(this, arg);

  @override
  R acceptReference<R>(MemberReferenceVisitor<R> v) =>
      v.visitConstructorReference(this);

  @override
  void visitChildren(Visitor v) {
    visitList(annotations, v);
    name.accept(v);
    visitList(initializers, v);
    function.accept(v);
  }

  @override
  void transformChildren(Transformer v) {
    v.transformList(annotations, this);
    v.transformList(initializers, this);
    // ignore: unnecessary_null_comparison
    if (function != null) {
      function = v.transform(function);
      function.parent = this;
    }
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    v.transformExpressionList(annotations, this);
    v.transformInitializerList(initializers, this);
    // ignore: unnecessary_null_comparison
    if (function != null) {
      function = v.transform(function);
      function.parent = this;
    }
  }

  @override
  DartType get getterType => const NeverType.nonNullable();

  @override
  DartType get setterType => const NeverType.nonNullable();

  @override
  Location? _getLocationInEnclosingFile(int offset) {
    return _getLocationInComponent(enclosingComponent, fileUri, offset);
  }
}

/// Residue of a redirecting factory constructor for the linking phase.
///
/// In the following example, `bar` is a redirecting factory constructor.
///
///     class A {
///       A.foo();
///       factory A.bar() = A.foo;
///     }
///
/// An invocation of `new A.bar()` has the same effect as an invocation of
/// `new A.foo()`.  In Kernel, the invocations of `bar` are replaced with
/// invocations of `foo`, and after it is done, the redirecting constructor can
/// be removed from the class.  However, it is needed during the linking phase,
/// because other modules can refer to that constructor.
///
/// [RedirectingFactoryConstructor]s contain the necessary information for
/// linking and are treated as non-runnable members of classes that merely serve
/// as containers for that information.
///
/// Redirecting factory constructors can be unnamed.  In this case, the name is
/// an empty string (in a [Name]).
class RedirectingFactoryConstructor extends Member {
  int flags = 0;

  /// [RedirectingFactoryConstructor]s may redirect to constructors or factories
  /// of instantiated generic types, that is, generic types with supplied type
  /// arguments.  The supplied type arguments are stored in this field.
  final List<DartType> typeArguments;

  /// Reference to the constructor or the factory that this
  /// [RedirectingFactoryConstructor] redirects to.
  // TODO(johnniwinther): Make this non-nullable.
  Reference? targetReference;

  /// [typeParameters] are duplicates of the type parameters of the enclosing
  /// class.  Because [RedirectingFactoryConstructor]s aren't instance members,
  /// references to the type parameters of the enclosing class in the
  /// redirection target description are encoded with references to the elements
  /// of [typeParameters].
  List<TypeParameter> typeParameters;

  /// Positional parameters of [RedirectingFactoryConstructor]s should be
  /// compatible with that of the target constructor.
  List<VariableDeclaration> positionalParameters;
  int requiredParameterCount;

  /// Named parameters of [RedirectingFactoryConstructor]s should be compatible
  /// with that of the target constructor.
  List<VariableDeclaration> namedParameters;

  RedirectingFactoryConstructor(this.targetReference,
      {required Name name,
      bool isConst: false,
      bool isExternal: false,
      int transformerFlags: 0,
      List<DartType>? typeArguments,
      List<TypeParameter>? typeParameters,
      List<VariableDeclaration>? positionalParameters,
      List<VariableDeclaration>? namedParameters,
      int? requiredParameterCount,
      required Uri fileUri,
      Reference? reference})
      : this.typeArguments = typeArguments ?? <DartType>[],
        this.typeParameters = typeParameters ?? <TypeParameter>[],
        this.positionalParameters =
            positionalParameters ?? <VariableDeclaration>[],
        this.namedParameters = namedParameters ?? <VariableDeclaration>[],
        this.requiredParameterCount =
            requiredParameterCount ?? positionalParameters?.length ?? 0,
        super(name, fileUri, reference) {
    setParents(this.typeParameters, this);
    setParents(this.positionalParameters, this);
    setParents(this.namedParameters, this);
    this.isConst = isConst;
    this.isExternal = isExternal;
    this.transformerFlags = transformerFlags;
  }

  @override
  Class get enclosingClass => parent as Class;

  static const int FlagConst = 1 << 0; // Must match serialized bit positions.
  static const int FlagExternal = 1 << 1;
  static const int FlagNonNullableByDefault = 1 << 2;

  @override
  bool get isConst => flags & FlagConst != 0;

  @override
  bool get isExternal => flags & FlagExternal != 0;

  void set isConst(bool value) {
    flags = value ? (flags | FlagConst) : (flags & ~FlagConst);
  }

  @override
  void set isExternal(bool value) {
    flags = value ? (flags | FlagExternal) : (flags & ~FlagExternal);
  }

  @override
  bool get isInstanceMember => false;

  @override
  bool get hasGetter => false;

  @override
  bool get hasSetter => false;

  @override
  bool get isExtensionMember => false;

  bool get isUnresolved => targetReference == null;

  @override
  bool get isNonNullableByDefault => flags & FlagNonNullableByDefault != 0;

  @override
  void set isNonNullableByDefault(bool value) {
    flags = value
        ? (flags | FlagNonNullableByDefault)
        : (flags & ~FlagNonNullableByDefault);
  }

  Member? get target => targetReference?.asMember;

  void set target(Member? member) {
    assert(member is Constructor ||
        (member is Procedure && member.kind == ProcedureKind.Factory));
    targetReference = getMemberReferenceGetter(member);
  }

  @override
  R accept<R>(MemberVisitor<R> v) => v.visitRedirectingFactoryConstructor(this);

  @override
  R accept1<R, A>(MemberVisitor1<R, A> v, A arg) =>
      v.visitRedirectingFactoryConstructor(this, arg);

  @override
  R acceptReference<R>(MemberReferenceVisitor<R> v) =>
      v.visitRedirectingFactoryConstructorReference(this);

  @override
  void visitChildren(Visitor v) {
    visitList(annotations, v);
    target?.acceptReference(v);
    visitList(typeArguments, v);
    name.accept(v);
  }

  @override
  void transformChildren(Transformer v) {
    v.transformList(annotations, this);
    v.transformDartTypeList(typeArguments);
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    v.transformExpressionList(annotations, this);
    v.transformDartTypeList(typeArguments);
  }

  @override
  DartType get getterType => const NeverType.nonNullable();

  @override
  DartType get setterType => const NeverType.nonNullable();

  @override
  Location? _getLocationInEnclosingFile(int offset) {
    return _getLocationInComponent(enclosingComponent, fileUri, offset);
  }
}

/// Enum for the semantics of the `Procedure.stubTarget` property.
enum ProcedureStubKind {
  /// A regular procedure declared in source code.
  ///
  /// The stub target is `null`.
  Regular,

  /// An abstract procedure inserted to add `isCovariant` and
  /// `isGenericCovariantImpl` to parameters for a set of overridden members.
  ///
  /// The stub is inserted when not all of the overridden members agree on
  /// the covariance flags. For instance:
  ///
  ///     class A<T> {
  ///        void method1(num o) {}
  ///        void method2(T o) {}
  ///     }
  ///     class B {
  ///        void method1(covariant int o) {}
  ///        void method2(int o) {}
  ///     }
  ///     class C implements A<int>, B {
  ///        // Abstract forwarding stub needed because the parameter is
  ///        // covariant in `B.method1` but not in `A.method1`.
  ///        void method1(covariant num o);
  ///        // Abstract forwarding stub needed because the parameter is a
  ///        // generic covariant impl in `A.method2` but not in `B.method2`.
  ///        void method2(/*generic-covariant-impl*/ int o);
  ///     }
  ///
  /// The stub target is one of the overridden members.
  AbstractForwardingStub,

  /// A concrete procedure inserted to add `isCovariant` and
  /// `isGenericCovariantImpl` checks to parameters before calling the
  /// overridden member in the superclass.
  ///
  /// The stub is inserted when not all of the overridden members agree on
  /// the covariance flags and the overridden super class member does not
  /// have the same covariance flags. For instance:
  ///
  ///     class A<T> {
  ///        void method1(num o) {}
  ///        void method2(T o) {}
  ///     }
  ///     class B {
  ///        void method1(covariant int o) {}
  ///        void method2(int o) {}
  ///     }
  ///     class C extends A<int> implements B {
  ///        // Concrete forwarding stub needed because the parameter is
  ///        // covariant in `B.method1` but not in `A.method1`.
  ///        void method1(covariant num o) => super.method1(o);
  ///        // No need for a concrete forwarding stub for `A.method2` because
  ///        // it has the right covariance flags already.
  ///     }
  ///
  /// The stub target is the called superclass member.
  ConcreteForwardingStub,

  /// A concrete procedure inserted to forward calls to `noSuchMethod` for
  /// an inherited member that it does not implement.
  ///
  /// The stub is inserted when a class implements private members of another
  /// library or declares/inherits a user-defined `noSuchMethod` method. For
  /// instance:
  ///
  ///     // lib1:
  ///     class A {
  ///       void _privateMethod() {}
  ///     }
  ///     // lib2:
  ///     class B implements A {
  ///       // Forwarding stub inserted to forward calls to `A._privateMethod`.
  ///       void _privateMethod() => noSuchMethod(#_privateMethod, ...);
  ///     }
  ///     class C {
  ///       void method() {}
  ///     }
  ///     class D implements C {
  ///       noSuchMethod(o) { ... }
  ///       // Forwarding stub inserted to forward calls to `C.method`.
  ///       void method() => noSuchMethod(#method, ...);
  ///     }
  ///
  ///
  /// The stub target is `null` if the procedure preexisted as an abstract
  /// procedure. Otherwise the stub target is one of the inherited members.
  NoSuchMethodForwarder,

  /// An abstract procedure inserted to show the combined member signature type
  /// of set of overridden members.
  ///
  /// The stub is inserted when an opt-in member is inherited into an opt-out
  /// library or when NNBD_TOP_MERGE was used to compute the type of a merge
  /// point in an opt-in library. For instance:
  ///
  ///     // lib1: opt-in
  ///     class A {
  ///       int? method1() => null;
  ///       void method2(Object? o) {}
  ///     }
  ///     class B {
  ///       dynamic method2(dynamic o);
  ///     }
  ///     class C implements A, B {
  ///       // Member signature inserted for the NNBD_TOP_MERGE type of
  ///       // `A.method2` and `B.method2`.
  ///       Object? method2(Object? o);
  ///     }
  ///     // lib2: opt-out
  ///     class D extends A {
  ///       // Member signature inserted for the LEGACY_ERASURE type of
  ///       // `A.method1` and `A.method2` with types `int* Function()`
  ///       // and `void Function(Object*)`, respectively.
  ///       int method1();
  ///       void method2(Object o);
  ///     }
  ///
  /// The stub target is one of the overridden members.
  MemberSignature,

  /// An abstract procedure inserted for the application of an abstract mixin
  /// member.
  ///
  /// The stub is inserted when an abstract member is mixed into a mixin
  /// application. For instance:
  ///
  ///     class Super {}
  ///     abstract class Mixin {
  ///        void method();
  ///     }
  ///     class Class = Super with Mixin
  ///       // An abstract mixin stub for `A.method` is added to `Class`
  ///       void method();
  ///     ;
  ///
  /// This is added to ensure that interface targets are resolved consistently
  /// in face of cloning. For instance, without the abstract mixin stub, this
  /// call:
  ///
  ///     method(Class c) => c.method();
  ///
  /// would use `Mixin.method` as its target, but after loading from a VM .dill
  /// (which clones all mixin members) the call would resolve to `Class.method`
  /// instead. By adding the mixin stub to `Class`, all accesses both before
  /// and after .dill will point to `Class.method`.
  ///
  /// The stub target is the mixin member.
  AbstractMixinStub,

  /// A concrete procedure inserted for the application of a concrete mixin
  /// member. The implementation calls the mixin member via a super-call.
  ///
  /// The stub is inserted when a concrete member is mixed into a mixin
  /// application. For instance:
  ///
  ///     class Super {}
  ///     abstract class Mixin {
  ///        void method() {}
  ///     }
  ///     class Class = Super with Mixin
  ///       // A concrete mixin stub for `A.method` is added to `Class` which
  ///       // calls `A.method`.
  ///       void method() => super.method();
  ///     ;
  ///
  /// This is added to ensure that super accesses are resolved correctly, even
  /// in face of cloning. For instance, without the concrete mixin stub, this
  /// super call:
  ///
  ///     class Subclass extends Class {
  ///       method(Class c) => super.method();
  ///     }
  ///
  /// would use `Mixin.method` as its target, which would need to be updated to
  /// match the clone of the mixin member performed for instance by the VM. By
  /// adding the concrete mixin stub to `Class`, all accesses both before and
  /// after cloning will point to `Class.method`.
  ///
  /// The stub target is the called mixin member.
  ConcreteMixinStub,
}

/// A method, getter, setter, index-getter, index-setter, operator overloader,
/// or factory.
///
/// Procedures can have the static, abstract, and/or external modifier, although
/// only the static and external modifiers may be used together.
///
/// For non-static procedures the name is required for dynamic dispatch.
/// For external procedures the name is required for identifying the external
/// implementation.
///
/// For methods, getters, and setters the name is just as it was declared.
/// For setters this does not include a trailing `=`.
/// For index-getters/setters, this is `[]` and `[]=`.
/// For operators, this is the token for the operator, e.g. `+` or `==`,
/// except for the unary minus operator, whose name is `unary-`.
class Procedure extends Member {
  /// Start offset of the function in the source file it comes from.
  ///
  /// Note that this includes annotations if any.
  ///
  /// Valid values are from 0 and up, or -1 ([TreeNode.noOffset]) if the file
  /// start offset is not available (this is the default if none is specifically
  /// set).
  int startFileOffset = TreeNode.noOffset;

  final ProcedureKind kind;
  int flags = 0;

  @override
  FunctionNode function;

  // The function node's body might be lazily loaded, meaning that this value
  // might not be set correctly yet. Make sure the body is loaded before
  // returning anything.
  @override
  int get transformerFlags {
    function.body;
    return super.transformerFlags;
  }

  // The function node's body might be lazily loaded, meaning that this value
  // might get overwritten later (when the body is read). To avoid that read the
  // body now and only set the value afterwards.
  @override
  void set transformerFlags(int newValue) {
    function.body;
    super.transformerFlags = newValue;
  }

  // This function will set the transformer flags without loading the body.
  // Used when reading the binary. For other cases one should probably use
  // `transformerFlags = value;`.
  void setTransformerFlagsWithoutLazyLoading(int newValue) {
    super.transformerFlags = newValue;
  }

  ProcedureStubKind stubKind;
  Reference? stubTargetReference;

  Procedure(Name name, ProcedureKind kind, FunctionNode function,
      {bool isAbstract: false,
      bool isStatic: false,
      bool isExternal: false,
      bool isConst: false,
      bool isExtensionMember: false,
      bool isSynthetic: false,
      int transformerFlags: 0,
      required Uri fileUri,
      Reference? reference,
      ProcedureStubKind stubKind: ProcedureStubKind.Regular,
      Member? stubTarget})
      : this._byReferenceRenamed(name, kind, function,
            isAbstract: isAbstract,
            isStatic: isStatic,
            isExternal: isExternal,
            isConst: isConst,
            isExtensionMember: isExtensionMember,
            isSynthetic: isSynthetic,
            transformerFlags: transformerFlags,
            fileUri: fileUri,
            reference: reference,
            stubKind: stubKind,
            stubTargetReference:
                getMemberReferenceBasedOnProcedureKind(stubTarget, kind));

  Procedure._byReferenceRenamed(Name name, this.kind, this.function,
      {bool isAbstract: false,
      bool isStatic: false,
      bool isExternal: false,
      bool isConst: false,
      bool isExtensionMember: false,
      bool isSynthetic: false,
      int transformerFlags: 0,
      required Uri fileUri,
      Reference? reference,
      this.stubKind: ProcedureStubKind.Regular,
      this.stubTargetReference})
      // ignore: unnecessary_null_comparison
      : assert(kind != null),
        // ignore: unnecessary_null_comparison
        assert(function != null),
        super(name, fileUri, reference) {
    function.parent = this;
    this.isAbstract = isAbstract;
    this.isStatic = isStatic;
    this.isExternal = isExternal;
    this.isConst = isConst;
    this.isExtensionMember = isExtensionMember;
    this.isSynthetic = isSynthetic;
    setTransformerFlagsWithoutLazyLoading(transformerFlags);
    assert(!(isMemberSignature && stubTargetReference == null),
        "No member signature origin for member signature $this.");
    assert(
        !(memberSignatureOrigin is Procedure &&
            (memberSignatureOrigin as Procedure).isMemberSignature),
        "Member signature origin cannot be a member signature "
        "$memberSignatureOrigin for $this.");
  }

  static const int FlagStatic = 1 << 0; // Must match serialized bit positions.
  static const int FlagAbstract = 1 << 1;
  static const int FlagExternal = 1 << 2;
  static const int FlagConst = 1 << 3; // Only for external const factories.
  // TODO(29841): Remove this flag after the issue is resolved.
  static const int FlagRedirectingFactoryConstructor = 1 << 4;
  static const int FlagExtensionMember = 1 << 5;
  static const int FlagNonNullableByDefault = 1 << 6;
  static const int FlagSynthetic = 1 << 7;

  bool get isStatic => flags & FlagStatic != 0;

  @override
  bool get isAbstract => flags & FlagAbstract != 0;

  @override
  bool get isExternal => flags & FlagExternal != 0;

  /// True if this has the `const` modifier.  This is only possible for external
  /// constant factories, such as `String.fromEnvironment`.
  @override
  bool get isConst => flags & FlagConst != 0;

  /// If set, this flag indicates that this function's implementation exists
  /// solely for the purpose of type checking arguments and forwarding to
  /// [concreteForwardingStubTarget].
  ///
  /// Note that just because this bit is set doesn't mean that the function was
  /// not declared in the source; it's possible that this is a forwarding
  /// semi-stub (see isForwardingSemiStub).  To determine whether this function
  /// was present in the source, consult [isSyntheticForwarder].
  bool get isForwardingStub =>
      stubKind == ProcedureStubKind.AbstractForwardingStub ||
      stubKind == ProcedureStubKind.ConcreteForwardingStub;

  /// If set, this flag indicates that although this function is a forwarding
  /// stub, it was present in the original source as an abstract method.
  bool get isForwardingSemiStub => !isSynthetic && isForwardingStub;

  /// If set, this method is a class member added to show the type of an
  /// inherited member.
  ///
  /// This is used when the type of the inherited member cannot be computed
  /// directly from the member(s) in the supertypes. For instance in case of
  /// an nnbd opt-out class inheriting from an nnbd opt-in class; here all nnbd-
  /// aware types are replaced with legacy types in the inherited signature.
  bool get isMemberSignature => stubKind == ProcedureStubKind.MemberSignature;

  // Indicates if this [Procedure] represents a redirecting factory constructor
  // and doesn't have a runnable body.
  bool get isRedirectingFactoryConstructor {
    return flags & FlagRedirectingFactoryConstructor != 0;
  }

  /// If set, this flag indicates that this function was not present in the
  /// source, and it exists solely for the purpose of type checking arguments
  /// and forwarding to [concreteForwardingStubTarget].
  bool get isSyntheticForwarder => isForwardingStub && !isForwardingSemiStub;
  bool get isSynthetic => flags & FlagSynthetic != 0;

  bool get isNoSuchMethodForwarder =>
      stubKind == ProcedureStubKind.NoSuchMethodForwarder;

  @override
  bool get isExtensionMember => flags & FlagExtensionMember != 0;

  void set isStatic(bool value) {
    flags = value ? (flags | FlagStatic) : (flags & ~FlagStatic);
  }

  void set isAbstract(bool value) {
    flags = value ? (flags | FlagAbstract) : (flags & ~FlagAbstract);
  }

  @override
  void set isExternal(bool value) {
    flags = value ? (flags | FlagExternal) : (flags & ~FlagExternal);
  }

  void set isConst(bool value) {
    flags = value ? (flags | FlagConst) : (flags & ~FlagConst);
  }

  void set isRedirectingFactoryConstructor(bool value) {
    flags = value
        ? (flags | FlagRedirectingFactoryConstructor)
        : (flags & ~FlagRedirectingFactoryConstructor);
  }

  void set isExtensionMember(bool value) {
    flags =
        value ? (flags | FlagExtensionMember) : (flags & ~FlagExtensionMember);
  }

  void set isSynthetic(bool value) {
    flags = value ? (flags | FlagSynthetic) : (flags & ~FlagSynthetic);
  }

  @override
  bool get isInstanceMember => !isStatic;

  bool get isGetter => kind == ProcedureKind.Getter;
  bool get isSetter => kind == ProcedureKind.Setter;
  bool get isAccessor => isGetter || isSetter;

  @override
  bool get hasGetter => kind != ProcedureKind.Setter;

  @override
  bool get hasSetter => kind == ProcedureKind.Setter;

  bool get isFactory => kind == ProcedureKind.Factory;

  @override
  bool get isNonNullableByDefault => flags & FlagNonNullableByDefault != 0;

  @override
  void set isNonNullableByDefault(bool value) {
    flags = value
        ? (flags | FlagNonNullableByDefault)
        : (flags & ~FlagNonNullableByDefault);
  }

  Member? get concreteForwardingStubTarget =>
      stubKind == ProcedureStubKind.ConcreteForwardingStub
          ? stubTargetReference?.asMember
          : null;

  Member? get abstractForwardingStubTarget =>
      stubKind == ProcedureStubKind.AbstractForwardingStub
          ? stubTargetReference?.asMember
          : null;

  Member? get stubTarget => stubTargetReference?.asMember;

  void set stubTarget(Member? target) {
    stubTargetReference = getMemberReferenceBasedOnProcedureKind(target, kind);
  }

  @override
  Member? get memberSignatureOrigin =>
      stubKind == ProcedureStubKind.MemberSignature
          ? stubTargetReference?.asMember
          : null;

  @override
  R accept<R>(MemberVisitor<R> v) => v.visitProcedure(this);

  @override
  R accept1<R, A>(MemberVisitor1<R, A> v, A arg) => v.visitProcedure(this, arg);

  @override
  R acceptReference<R>(MemberReferenceVisitor<R> v) =>
      v.visitProcedureReference(this);

  @override
  void visitChildren(Visitor v) {
    visitList(annotations, v);
    name.accept(v);
    function.accept(v);
  }

  @override
  void transformChildren(Transformer v) {
    v.transformList(annotations, this);
    // ignore: unnecessary_null_comparison
    if (function != null) {
      function = v.transform(function);
      function.parent = this;
    }
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    v.transformExpressionList(annotations, this);
    // ignore: unnecessary_null_comparison
    if (function != null) {
      function = v.transform(function);
      function.parent = this;
    }
  }

  @override
  DartType get getterType {
    return isGetter
        ? function.returnType
        : function.computeFunctionType(enclosingLibrary.nonNullable);
  }

  @override
  DartType get setterType {
    return isSetter
        ? function.positionalParameters[0].type
        : const NeverType.nonNullable();
  }

  @override
  Location? _getLocationInEnclosingFile(int offset) {
    return _getLocationInComponent(enclosingComponent, fileUri, offset);
  }
}

enum ProcedureKind {
  Method,
  Getter,
  Setter,
  Operator,
  Factory,
}

// ------------------------------------------------------------------------
//                     CONSTRUCTOR INITIALIZERS
// ------------------------------------------------------------------------

/// Part of an initializer list in a constructor.
abstract class Initializer extends TreeNode {
  /// True if this is a synthetic constructor initializer.
  @informative
  bool isSynthetic = false;

  @override
  R accept<R>(InitializerVisitor<R> v);

  @override
  R accept1<R, A>(InitializerVisitor1<R, A> v, A arg);
}

/// An initializer with a compile-time error.
///
/// Should throw an exception at runtime.
//
// DESIGN TODO: The frontend should use this in a lot more cases to catch
// invalid cases.
class InvalidInitializer extends Initializer {
  @override
  R accept<R>(InitializerVisitor<R> v) => v.visitInvalidInitializer(this);

  @override
  R accept1<R, A>(InitializerVisitor1<R, A> v, A arg) =>
      v.visitInvalidInitializer(this, arg);

  @override
  void visitChildren(Visitor v) {}

  @override
  void transformChildren(Transformer v) {}

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {}

  @override
  String toString() {
    return "InvalidInitializer(${toStringInternal()})";
  }

  @override
  void toTextInternal(AstPrinter printer) {
    // TODO(johnniwinther): Implement this.
  }
}

/// A field assignment `field = value` occurring in the initializer list of
/// a constructor.
///
/// This node has nothing to do with declaration-site field initializers; those
/// are [Expression]s stored in [Field.initializer].
//
// TODO: The frontend should check that all final fields are initialized
//  exactly once, and that no fields are assigned twice in the initializer list.
class FieldInitializer extends Initializer {
  /// Reference to the field being initialized.  Not null.
  Reference fieldReference;
  Expression value;

  FieldInitializer(Field field, Expression value)
      : this.byReference(
            // getterReference is used since this refers to the field itself
            field.getterReference,
            value);

  FieldInitializer.byReference(this.fieldReference, this.value) {
    value.parent = this;
  }

  Field get field => fieldReference.asField;

  void set field(Field field) {
    fieldReference = field.getterReference;
  }

  @override
  R accept<R>(InitializerVisitor<R> v) => v.visitFieldInitializer(this);

  @override
  R accept1<R, A>(InitializerVisitor1<R, A> v, A arg) =>
      v.visitFieldInitializer(this, arg);

  @override
  void visitChildren(Visitor v) {
    field.acceptReference(v);
    value.accept(v);
  }

  @override
  void transformChildren(Transformer v) {
    // ignore: unnecessary_null_comparison
    if (value != null) {
      value = v.transform(value);
      value.parent = this;
    }
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    // ignore: unnecessary_null_comparison
    if (value != null) {
      value = v.transform(value);
      value.parent = this;
    }
  }

  @override
  String toString() {
    return "FieldInitializer(${toStringInternal()})";
  }

  @override
  void toTextInternal(AstPrinter printer) {
    // TODO(johnniwinther): Implement this.
  }
}

/// A super call `super(x,y)` occurring in the initializer list of a
/// constructor.
///
/// There are no type arguments on this call.
//
// TODO: The frontend should check that there is no more than one super call.
//
// DESIGN TODO: Consider if the frontend should insert type arguments derived
// from the extends clause.
class SuperInitializer extends Initializer {
  /// Reference to the constructor being invoked in the super class. Not null.
  Reference targetReference;
  Arguments arguments;

  SuperInitializer(Constructor target, Arguments arguments)
      : this.byReference(
            // Getter vs setter doesn't matter for constructors.
            getNonNullableMemberReferenceGetter(target),
            arguments);

  SuperInitializer.byReference(this.targetReference, this.arguments) {
    arguments.parent = this;
  }

  Constructor get target => targetReference.asConstructor;

  void set target(Constructor target) {
    // Getter vs setter doesn't matter for constructors.
    targetReference = getNonNullableMemberReferenceGetter(target);
  }

  @override
  R accept<R>(InitializerVisitor<R> v) => v.visitSuperInitializer(this);

  @override
  R accept1<R, A>(InitializerVisitor1<R, A> v, A arg) =>
      v.visitSuperInitializer(this, arg);

  @override
  void visitChildren(Visitor v) {
    target.acceptReference(v);
    arguments.accept(v);
  }

  @override
  void transformChildren(Transformer v) {
    // ignore: unnecessary_null_comparison
    if (arguments != null) {
      arguments = v.transform(arguments);
      arguments.parent = this;
    }
  }

  @override
  void transformOrRemoveChildren(RemovingTransformer v) {
    // ignore: unnecessary_null_comparison
    if (arguments != null) {
      arguments = v.transform(arguments);
      arguments.parent = this;
    }
  }

  @override
  String toString() {
    return "SuperInitializer(${toStringInternal()})";
  }

  @override
  void toTextInternal(AstPrinter printer) {
    // TODO(johnniwinther): Implement this.
  }
}

/// A redirecting call `this(x,y)` occurring in the initializer list of
/// a constructor.
//
// TODO: The frontend should check that this is the only initializer and if the
// constructor has a body or if there is a cycle in the initializer calls.
class RedirectingInitializer extends Initializer {
  /// Reference to the constructor being invoked in the same class. Not null.
  Reference targetReference;
  Arguments arguments;

  RedirectingInitializer(Constructor target, Arguments arguments)
      : this.byReference(
            // Getter vs setter doesn't matter for constructors.
            getNonNullableMemberReferenceGetter(target),
            arguments);

  RedirectingInitializer.byReference(this.targetReference, this.arguments) {
    arguments.parent = this;
  }

  Constructor get target => targetReference.asConstructor;

  void set target(Constructor target) {
    // Getter vs setter doesn't matter for constructors.
    targetReference = getNonNullableMemberReferenceGetter(target);
  }

  @override
  R accept<R>(InitializerVisitor<R> v) => v.visitRedirectingInitializer(this);

  @override
  R accept1<R, A>(InitializerVisitor1<R, A> v, A arg) =>
      v.visitRedirectingInitializer(this, arg);

  @override
  void visitChildren(Visitor v) {
    target.acceptReference(v);
    arguments.accept(v);
  }

  @override
  void transformChildren(Transformer v) {
    // ignore: unnecessary_null_comparison
    if (arguments != null) {
      arguments = v.transform(arguments);
      arguments.parent = this;
    <