// Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:kernel/ast.dart'
    show Arguments, Expression, InvalidExpression, Node;

import '../../scanner/token.dart' show Token;

import '../constant_context.dart' show ConstantContext;

import '../fasta_codes.dart'
    show
        LocatedMessage,
        Message,
        messageCannotAssignToParenthesizedExpression,
        messageCannotAssignToSuper,
        messageInvalidUseOfNullAwareAccess,
        messageLoadLibraryTakesNoArguments,
        messageNotAConstantExpression,
        messageNotAnLvalue,
        messageSuperAsExpression,
        templateConstructorNotFound,
        templateNotConstantExpression,
        templateSuperclassHasNoConstructor,
        templateThisOrSuperAccessInFieldInitializer;

import '../messages.dart' show Message, noLength;

import '../names.dart' show callName, equalsName, indexGetName, indexSetName;

import '../parser.dart' show lengthForToken, offsetForToken;

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

import '../scope.dart' show AmbiguousBuilder;

import 'body_builder.dart' show noLocation;

import 'constness.dart' show Constness;

import 'expression_generator.dart'
    show
        ContextAwareGenerator,
        DeferredAccessGenerator,
        DelayedAssignment,
        DelayedPostfixIncrement,
        ErroneousExpressionGenerator,
        ExpressionGenerator,
        Generator,
        IndexedAccessGenerator,
        LoadLibraryGenerator,
        NullAwarePropertyAccessGenerator,
        ParserErrorGenerator,
        PrefixUseGenerator,
        PropertyAccessGenerator,
        ReadOnlyAccessGenerator,
        StaticAccessGenerator,
        SuperIndexedAccessGenerator,
        SuperPropertyAccessGenerator,
        ThisIndexedAccessGenerator,
        ThisPropertyAccessGenerator,
        TypeUseGenerator,
        UnexpectedQualifiedUseGenerator,
        UnlinkedGenerator,
        UnresolvedNameGenerator,
        VariableUseGenerator;

import 'expression_generator_helper.dart' show ExpressionGeneratorHelper;

import 'forest.dart' show Forest;

import 'kernel_builder.dart'
    show
        KernelTypeBuilder,
        LoadLibraryBuilder,
        PrefixBuilder,
        UnlinkedDeclaration,
        UnresolvedType;

import 'kernel_api.dart' show NameSystem, printNodeOn, printQualifiedNameOn;

import 'kernel_ast_api.dart'
    show
        ComplexAssignmentJudgment,
        Constructor,
        DartType,
        Field,
        Initializer,
        Let,
        LoadLibraryTearOffJudgment,
        Member,
        MethodInvocationJudgment,
        Name,
        NullAwarePropertyGetJudgment,
        Procedure,
        PropertyGet,
        PropertySet,
        StaticSet,
        SuperMethodInvocation,
        SuperMethodInvocationJudgment,
        SuperPropertyGetJudgment,
        SuperPropertySet,
        TreeNode,
        TypeParameter,
        VariableDeclaration,
        VariableDeclarationJudgment,
        VariableGet,
        VariableGetJudgment,
        VariableSet;

import 'kernel_builder.dart'
    show
        Declaration,
        KernelClassBuilder,
        KernelInvalidTypeBuilder,
        LoadLibraryBuilder,
        PrefixBuilder,
        TypeDeclarationBuilder;

import 'kernel_shadow_ast.dart' as shadow
    show PropertyAssignmentJudgment, SyntheticWrapper;

part 'kernel_expression_generator_impl.dart';

abstract class KernelExpressionGenerator implements ExpressionGenerator {
  ExpressionGeneratorHelper get helper;

  Token get token;

  Forest get forest;

  String get plainNameForRead;

  @override
  Expression buildSimpleRead() {
    return _finish(_makeSimpleRead(), null);
  }

  @override
  Expression buildAssignment(Expression value, {bool voidContext: false}) {
    var complexAssignment = startComplexAssignment(value);
    return _finish(_makeSimpleWrite(value, voidContext, complexAssignment),
        complexAssignment);
  }

  @override
  Expression buildNullAwareAssignment(
      Expression value, DartType type, int offset,
      {bool voidContext: false}) {
    var complexAssignment = startComplexAssignment(value);
    if (voidContext) {
      var nullAwareCombiner = forest.conditionalExpression(
          buildIsNull(_makeRead(complexAssignment), offset, helper),
          null,
          _makeWrite(value, false, complexAssignment),
          null,
          forest.literalNull(null)..fileOffset = offset)
        ..fileOffset = offset;
      complexAssignment?.nullAwareCombiner = nullAwareCombiner;
      return _finish(nullAwareCombiner, complexAssignment);
    }
    var tmp = new VariableDeclaration.forValue(_makeRead(complexAssignment));
    var nullAwareCombiner = forest.conditionalExpression(
        buildIsNull(new VariableGet(tmp), offset, helper),
        null,
        _makeWrite(value, false, complexAssignment),
        null,
        new VariableGet(tmp))
      ..fileOffset = offset;
    complexAssignment?.nullAwareCombiner = nullAwareCombiner;
    return _finish(makeLet(tmp, nullAwareCombiner), complexAssignment);
  }

  @override
  Expression buildCompoundAssignment(Name binaryOperator, Expression value,
      {int offset: TreeNode.noOffset,
      bool voidContext: false,
      Procedure interfaceTarget,
      bool isPreIncDec: false,
      bool isPostIncDec: false}) {
    var complexAssignment = startComplexAssignment(value);
    complexAssignment?.isPreIncDec = isPreIncDec;
    complexAssignment?.isPostIncDec = isPostIncDec;
    var combiner = makeBinary(_makeRead(complexAssignment), binaryOperator,
        interfaceTarget, value, helper,
        offset: offset);
    complexAssignment?.combiner = combiner;
    return _finish(_makeWrite(combiner, voidContext, complexAssignment),
        complexAssignment);
  }

  @override
  Expression buildPrefixIncrement(Name binaryOperator,
      {int offset: TreeNode.noOffset,
      bool voidContext: false,
      Procedure interfaceTarget}) {
    return buildCompoundAssignment(
        binaryOperator, forest.literalInt(1, null)..fileOffset = offset,
        offset: offset,
        voidContext: voidContext,
        interfaceTarget: interfaceTarget,
        isPreIncDec: true);
  }

  @override
  Expression buildPostfixIncrement(Name binaryOperator,
      {int offset: TreeNode.noOffset,
      bool voidContext: false,
      Procedure interfaceTarget}) {
    if (voidContext) {
      return buildCompoundAssignment(
          binaryOperator, forest.literalInt(1, null)..fileOffset = offset,
          offset: offset,
          voidContext: voidContext,
          interfaceTarget: interfaceTarget,
          isPostIncDec: true);
    }
    var rhs = forest.literalInt(1, null)..fileOffset = offset;
    var complexAssignment = startComplexAssignment(rhs);
    var value = new VariableDeclaration.forValue(_makeRead(complexAssignment));
    valueAccess() => new VariableGet(value);
    var combiner = makeBinary(
        valueAccess(), binaryOperator, interfaceTarget, rhs, helper,
        offset: offset);
    complexAssignment?.combiner = combiner;
    complexAssignment?.isPostIncDec = true;
    var dummy = new VariableDeclarationJudgment.forValue(
        _makeWrite(combiner, true, complexAssignment),
        helper.functionNestingLevel);
    return _finish(
        makeLet(value, makeLet(dummy, valueAccess())), complexAssignment);
  }

  @override
  Expression makeInvalidRead() {
    return helper.wrapSyntheticExpression(
        helper.throwNoSuchMethodError(
            forest.literalNull(token),
            plainNameForRead,
            forest.argumentsEmpty(noLocation),
            offsetForToken(token),
            isGetter: true),
        offsetForToken(token));
  }

  @override
  Expression makeInvalidWrite(Expression value) {
    return helper.wrapSyntheticExpression(
        helper.throwNoSuchMethodError(
            forest.literalNull(token),
            plainNameForRead,
            forest.arguments(<Expression>[value], noLocation),
            offsetForToken(token),
            isSetter: true),
        offsetForToken(token));
  }

  Expression _makeSimpleRead() => _makeRead(null);

  Expression _makeSimpleWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    return _makeWrite(value, voidContext, complexAssignment);
  }

  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    Expression read = makeInvalidRead();
    if (complexAssignment != null) {
      read = helper.desugarSyntheticExpression(read);
      complexAssignment.read = read;
    }
    return read;
  }

  Expression _makeWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    Expression write = makeInvalidWrite(value);
    if (complexAssignment != null) {
      write = helper.desugarSyntheticExpression(write);
      complexAssignment.write = write;
    }
    return write;
  }

  Expression _finish(
      Expression body, ComplexAssignmentJudgment complexAssignment) {
    if (complexAssignment != null) {
      complexAssignment.desugared = body;
      return complexAssignment;
    } else {
      return body;
    }
  }

  /// Creates a data structure for tracking the desugaring of a complex
  /// assignment expression whose right hand side is [rhs].
  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) =>
      shadow.SyntheticWrapper.wrapIllegalAssignment(rhs);
}

abstract class KernelGenerator = Generator with KernelExpressionGenerator;

class KernelVariableUseGenerator extends KernelGenerator
    with VariableUseGenerator {
  final VariableDeclaration variable;

  final DartType promotedType;

  KernelVariableUseGenerator(ExpressionGeneratorHelper helper, Token token,
      this.variable, this.promotedType)
      : super(helper, token);

  @override
  String get plainNameForRead => variable.name;

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    var fact = helper.typePromoter
        ?.getFactForAccess(variable, helper.functionNestingLevel);
    var scope = helper.typePromoter?.currentScope;
    var read = new VariableGetJudgment(variable, fact, scope)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.read = read;
    return read;
  }

  @override
  Expression _makeWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    helper.typePromoter?.mutateVariable(variable, helper.functionNestingLevel);
    var write = variable.isFinal || variable.isConst
        ? makeInvalidWrite(value)
        : new VariableSet(variable, value)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    return helper.buildMethodInvocation(buildSimpleRead(), callName, arguments,
        adjustForImplicitCall(plainNameForRead, offset),
        isImplicitCall: true);
  }

  @override
  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) {
    return shadow.SyntheticWrapper.wrapVariableAssignment(rhs)
      ..fileOffset = offsetForToken(token);
  }

  @override
  void printOn(StringSink sink) {
    NameSystem syntheticNames = new NameSystem();
    sink.write(", variable: ");
    printNodeOn(variable, sink, syntheticNames: syntheticNames);
    sink.write(", promotedType: ");
    printNodeOn(promotedType, sink, syntheticNames: syntheticNames);
  }
}

class KernelPropertyAccessGenerator extends KernelGenerator
    with PropertyAccessGenerator {
  final Expression receiver;

  final Name name;

  final Member getter;

  final Member setter;

  VariableDeclaration _receiverVariable;

  KernelPropertyAccessGenerator.internal(ExpressionGeneratorHelper helper,
      Token token, this.receiver, this.name, this.getter, this.setter)
      : super(helper, token);

  @override
  String get plainNameForRead => name.name;

  receiverAccess() {
    _receiverVariable ??= new VariableDeclaration.forValue(receiver);
    return new VariableGet(_receiverVariable)
      ..fileOffset = offsetForToken(token);
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    return helper.buildMethodInvocation(receiver, name, arguments, offset);
  }

  @override
  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) =>
      shadow.SyntheticWrapper.wrapPropertyAssignment(receiver, rhs);

  @override
  void printOn(StringSink sink) {
    NameSystem syntheticNames = new NameSystem();
    sink.write(", _receiverVariable: ");
    printNodeOn(_receiverVariable, sink, syntheticNames: syntheticNames);
    sink.write(", receiver: ");
    printNodeOn(receiver, sink, syntheticNames: syntheticNames);
    sink.write(", name: ");
    sink.write(name.name);
    sink.write(", getter: ");
    printQualifiedNameOn(getter, sink, syntheticNames: syntheticNames);
    sink.write(", setter: ");
    printQualifiedNameOn(setter, sink, syntheticNames: syntheticNames);
  }

  @override
  Expression _makeSimpleRead() {
    return new PropertyGet(receiver, name, getter)
      ..fileOffset = offsetForToken(token);
  }

  @override
  Expression _makeSimpleWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    var write = new PropertySet(receiver, name, value, setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    var read = new PropertyGet(receiverAccess(), name, getter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.read = read;
    return read;
  }

  @override
  Expression _makeWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    var write = new PropertySet(receiverAccess(), name, value, setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  @override
  Expression _finish(
      Expression body, ComplexAssignmentJudgment complexAssignment) {
    return super._finish(makeLet(_receiverVariable, body), complexAssignment);
  }
}

class KernelThisPropertyAccessGenerator extends KernelGenerator
    with ThisPropertyAccessGenerator {
  final Name name;

  final Member getter;

  final Member setter;

  KernelThisPropertyAccessGenerator(ExpressionGeneratorHelper helper,
      Token token, this.name, this.getter, this.setter)
      : super(helper, token);

  @override
  String get plainNameForRead => name.name;

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    if (getter == null) {
      helper.warnUnresolvedGet(name, offsetForToken(token));
    }
    var read = new PropertyGet(forest.thisExpression(token), name, getter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.read = read;
    return read;
  }

  @override
  Expression _makeWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    if (setter == null) {
      helper.warnUnresolvedSet(name, offsetForToken(token));
    }
    var write =
        new PropertySet(forest.thisExpression(token), name, value, setter)
          ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    Member interfaceTarget = getter;
    if (interfaceTarget == null) {
      helper.warnUnresolvedMethod(name, offset);
    }
    if (interfaceTarget is Field) {
      // TODO(ahe): In strong mode we should probably rewrite this to
      // `this.name.call(arguments)`.
      interfaceTarget = null;
    }
    return helper.buildMethodInvocation(
        forest.thisExpression(null), name, arguments, offset,
        interfaceTarget: interfaceTarget);
  }

  @override
  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) =>
      shadow.SyntheticWrapper.wrapPropertyAssignment(null, rhs);

  @override
  void printOn(StringSink sink) {
    NameSystem syntheticNames = new NameSystem();
    sink.write(", name: ");
    sink.write(name.name);
    sink.write(", getter: ");
    printQualifiedNameOn(getter, sink, syntheticNames: syntheticNames);
    sink.write(", setter: ");
    printQualifiedNameOn(setter, sink, syntheticNames: syntheticNames);
  }
}

class KernelNullAwarePropertyAccessGenerator extends KernelGenerator
    with NullAwarePropertyAccessGenerator {
  final VariableDeclaration receiver;

  final Expression receiverExpression;

  final Name name;

  final Member getter;

  final Member setter;

  final DartType type;

  KernelNullAwarePropertyAccessGenerator(
      ExpressionGeneratorHelper helper,
      Token token,
      this.receiverExpression,
      this.name,
      this.getter,
      this.setter,
      this.type)
      : this.receiver = makeOrReuseVariable(receiverExpression),
        super(helper, token);

  Expression receiverAccess() => new VariableGet(receiver);

  @override
  String get plainNameForRead => name.name;

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    var read = new PropertyGet(receiverAccess(), name, getter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.read = read;
    return read;
  }

  @override
  Expression _makeWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    var write = new PropertySet(receiverAccess(), name, value, setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  @override
  Expression _finish(
      Expression body, ComplexAssignmentJudgment complexAssignment) {
    var offset = offsetForToken(token);
    var nullAwareGuard = forest.conditionalExpression(
        buildIsNull(receiverAccess(), offset, helper),
        null,
        forest.literalNull(null)..fileOffset = offset,
        null,
        body)
      ..fileOffset = offset;
    if (complexAssignment != null) {
      body = makeLet(receiver, nullAwareGuard);
      shadow.PropertyAssignmentJudgment kernelPropertyAssign =
          complexAssignment;
      kernelPropertyAssign.nullAwareGuard = nullAwareGuard;
      kernelPropertyAssign.desugared = body;
      return kernelPropertyAssign;
    } else {
      return new NullAwarePropertyGetJudgment(receiver, nullAwareGuard)
        ..fileOffset = offset;
    }
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    return unsupported("doInvocation", offset, uri);
  }

  @override
  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) =>
      shadow.SyntheticWrapper.wrapPropertyAssignment(receiverExpression, rhs);

  @override
  void printOn(StringSink sink) {
    NameSystem syntheticNames = new NameSystem();
    sink.write(", receiver: ");
    printNodeOn(receiver, sink, syntheticNames: syntheticNames);
    sink.write(", receiverExpression: ");
    printNodeOn(receiverExpression, sink, syntheticNames: syntheticNames);
    sink.write(", name: ");
    sink.write(name.name);
    sink.write(", getter: ");
    printQualifiedNameOn(getter, sink, syntheticNames: syntheticNames);
    sink.write(", setter: ");
    printQualifiedNameOn(setter, sink, syntheticNames: syntheticNames);
    sink.write(", type: ");
    printNodeOn(type, sink, syntheticNames: syntheticNames);
  }
}

class KernelSuperPropertyAccessGenerator extends KernelGenerator
    with SuperPropertyAccessGenerator {
  final Name name;

  final Member getter;

  final Member setter;

  KernelSuperPropertyAccessGenerator(ExpressionGeneratorHelper helper,
      Token token, this.name, this.getter, this.setter)
      : super(helper, token);

  @override
  String get plainNameForRead => name.name;

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    if (getter == null) {
      helper.warnUnresolvedGet(name, offsetForToken(token), isSuper: true);
    }
    // TODO(ahe): Use [DirectPropertyGet] when possible.
    var read = new SuperPropertyGetJudgment(name, interfaceTarget: getter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.read = read;
    return read;
  }

  @override
  Expression _makeWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    if (setter == null) {
      helper.warnUnresolvedSet(name, offsetForToken(token), isSuper: true);
    }
    // TODO(ahe): Use [DirectPropertySet] when possible.
    var write = new SuperPropertySet(name, value, setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    if (helper.constantContext != ConstantContext.none) {
      // TODO(brianwilkerson) Fix the length
      helper.addProblem(messageNotAConstantExpression, offset, 1);
    }
    if (getter == null || isFieldOrGetter(getter)) {
      return helper.buildMethodInvocation(
          buildSimpleRead(), callName, arguments, offset,
          // This isn't a constant expression, but we have checked if a
          // constant expression error should be emitted already.
          isConstantExpression: true,
          isImplicitCall: true);
    } else {
      // TODO(ahe): This could be something like "super.property(...)" where
      // property is a setter.
      return unhandled("${getter.runtimeType}", "doInvocation", offset, uri);
    }
  }

  @override
  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) =>
      shadow.SyntheticWrapper.wrapPropertyAssignment(null, rhs, isSuper: true);

  @override
  void printOn(StringSink sink) {
    NameSystem syntheticNames = new NameSystem();
    sink.write(", name: ");
    sink.write(name.name);
    sink.write(", getter: ");
    printQualifiedNameOn(getter, sink, syntheticNames: syntheticNames);
    sink.write(", setter: ");
    printQualifiedNameOn(setter, sink, syntheticNames: syntheticNames);
  }
}

class KernelIndexedAccessGenerator extends KernelGenerator
    with IndexedAccessGenerator {
  final Expression receiver;

  final Expression index;

  final Procedure getter;

  final Procedure setter;

  VariableDeclaration receiverVariable;

  VariableDeclaration indexVariable;

  KernelIndexedAccessGenerator.internal(ExpressionGeneratorHelper helper,
      Token token, this.receiver, this.index, this.getter, this.setter)
      : super(helper, token);

  Expression indexAccess() {
    indexVariable ??= new VariableDeclaration.forValue(index);
    return new VariableGet(indexVariable)..fileOffset = offsetForToken(token);
  }

  Expression receiverAccess() {
    // We cannot reuse the receiver if it is a variable since it might be
    // reassigned in the index expression.
    receiverVariable ??= new VariableDeclaration.forValue(receiver);
    return new VariableGet(receiverVariable)
      ..fileOffset = offsetForToken(token);
  }

  @override
  Expression _makeSimpleRead() {
    var read = new MethodInvocationJudgment(receiver, indexGetName,
        forest.castArguments(forest.arguments(<Expression>[index], token)),
        interfaceTarget: getter)
      ..fileOffset = offsetForToken(token);
    return read;
  }

  @override
  Expression _makeSimpleWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    if (!voidContext) return _makeWriteAndReturn(value, complexAssignment);
    var write = new MethodInvocationJudgment(
        receiver,
        indexSetName,
        forest
            .castArguments(forest.arguments(<Expression>[index, value], token)),
        interfaceTarget: setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    var read = new MethodInvocationJudgment(
        receiverAccess(),
        indexGetName,
        forest.castArguments(
            forest.arguments(<Expression>[indexAccess()], token)),
        interfaceTarget: getter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.read = read;
    return read;
  }

  @override
  Expression _makeWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    if (!voidContext) return _makeWriteAndReturn(value, complexAssignment);
    var write = new MethodInvocationJudgment(
        receiverAccess(),
        indexSetName,
        forest.castArguments(
            forest.arguments(<Expression>[indexAccess(), value], token)),
        interfaceTarget: setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  // TODO(dmitryas): remove this method after the "[]=" operator of the Context
  // class is made to return a value.
  Expression _makeWriteAndReturn(
      Expression value, ComplexAssignmentJudgment complexAssignment) {
    // The call to []= does not return the value like direct-style assignments
    // do.  We need to bind the value in a let.
    var valueVariable = new VariableDeclaration.forValue(value);
    var write = new MethodInvocationJudgment(
        receiverAccess(),
        indexSetName,
        forest.castArguments(forest.arguments(
            <Expression>[indexAccess(), new VariableGet(valueVariable)],
            token)),
        interfaceTarget: setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    var dummy = new VariableDeclarationJudgment.forValue(
        write, helper.functionNestingLevel);
    return makeLet(
        valueVariable, makeLet(dummy, new VariableGet(valueVariable)));
  }

  @override
  Expression _finish(
      Expression body, ComplexAssignmentJudgment complexAssignment) {
    int offset = offsetForToken(token);
    return super._finish(
        makeLet(
            receiverVariable, makeLet(indexVariable, body)..fileOffset = offset)
          ..fileOffset = offset,
        complexAssignment);
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    return helper.buildMethodInvocation(
        buildSimpleRead(), callName, arguments, forest.readOffset(arguments),
        isImplicitCall: true);
  }

  @override
  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) =>
      shadow.SyntheticWrapper.wrapIndexAssignment(receiver, index, rhs);

  @override
  void printOn(StringSink sink) {
    NameSystem syntheticNames = new NameSystem();
    sink.write(", receiver: ");
    printNodeOn(receiver, sink, syntheticNames: syntheticNames);
    sink.write(", index: ");
    printNodeOn(index, sink, syntheticNames: syntheticNames);
    sink.write(", getter: ");
    printQualifiedNameOn(getter, sink, syntheticNames: syntheticNames);
    sink.write(", setter: ");
    printQualifiedNameOn(setter, sink, syntheticNames: syntheticNames);
    sink.write(", receiverVariable: ");
    printNodeOn(receiverVariable, sink, syntheticNames: syntheticNames);
    sink.write(", indexVariable: ");
    printNodeOn(indexVariable, sink, syntheticNames: syntheticNames);
  }
}

class KernelThisIndexedAccessGenerator extends KernelGenerator
    with ThisIndexedAccessGenerator {
  final Expression index;

  final Procedure getter;

  final Procedure setter;

  VariableDeclaration indexVariable;

  KernelThisIndexedAccessGenerator(ExpressionGeneratorHelper helper,
      Token token, this.index, this.getter, this.setter)
      : super(helper, token);

  Expression indexAccess() {
    indexVariable ??= new VariableDeclaration.forValue(index);
    return new VariableGet(indexVariable);
  }

  Expression _makeWriteAndReturn(
      Expression value, ComplexAssignmentJudgment complexAssignment) {
    var valueVariable = new VariableDeclaration.forValue(value);
    var write = new MethodInvocationJudgment(
        forest.thisExpression(token),
        indexSetName,
        forest.castArguments(forest.arguments(
            <Expression>[indexAccess(), new VariableGet(valueVariable)],
            token)),
        interfaceTarget: setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    var dummy = new VariableDeclaration.forValue(write);
    return makeLet(
        valueVariable, makeLet(dummy, new VariableGet(valueVariable)));
  }

  @override
  Expression _makeSimpleRead() {
    return new MethodInvocationJudgment(
        forest.thisExpression(token),
        indexGetName,
        forest.castArguments(forest.arguments(<Expression>[index], token)),
        interfaceTarget: getter)
      ..fileOffset = offsetForToken(token);
  }

  @override
  Expression _makeSimpleWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    if (!voidContext) return _makeWriteAndReturn(value, complexAssignment);
    var write = new MethodInvocationJudgment(
        forest.thisExpression(token),
        indexSetName,
        forest
            .castArguments(forest.arguments(<Expression>[index, value], token)),
        interfaceTarget: setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    var read = new MethodInvocationJudgment(
        forest.thisExpression(token),
        indexGetName,
        forest.castArguments(
            forest.arguments(<Expression>[indexAccess()], token)),
        interfaceTarget: getter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.read = read;
    return read;
  }

  @override
  Expression _makeWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    if (!voidContext) return _makeWriteAndReturn(value, complexAssignment);
    var write = new MethodInvocationJudgment(
        forest.thisExpression(token),
        indexSetName,
        forest.castArguments(
            forest.arguments(<Expression>[indexAccess(), value], token)),
        interfaceTarget: setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  @override
  Expression _finish(
      Expression body, ComplexAssignmentJudgment complexAssignment) {
    return super._finish(makeLet(indexVariable, body), complexAssignment);
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    return helper.buildMethodInvocation(
        buildSimpleRead(), callName, arguments, offset,
        isImplicitCall: true);
  }

  @override
  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) =>
      shadow.SyntheticWrapper.wrapIndexAssignment(null, index, rhs);

  @override
  void printOn(StringSink sink) {
    NameSystem syntheticNames = new NameSystem();
    sink.write(", index: ");
    printNodeOn(index, sink, syntheticNames: syntheticNames);
    sink.write(", getter: ");
    printQualifiedNameOn(getter, sink, syntheticNames: syntheticNames);
    sink.write(", setter: ");
    printQualifiedNameOn(setter, sink, syntheticNames: syntheticNames);
    sink.write(", indexVariable: ");
    printNodeOn(indexVariable, sink, syntheticNames: syntheticNames);
  }
}

class KernelSuperIndexedAccessGenerator extends KernelGenerator
    with SuperIndexedAccessGenerator {
  final Expression index;

  final Member getter;

  final Member setter;

  VariableDeclaration indexVariable;

  KernelSuperIndexedAccessGenerator(ExpressionGeneratorHelper helper,
      Token token, this.index, this.getter, this.setter)
      : super(helper, token);

  Expression indexAccess() {
    indexVariable ??= new VariableDeclaration.forValue(index);
    return new VariableGet(indexVariable);
  }

  Expression _makeWriteAndReturn(
      Expression value, ComplexAssignmentJudgment complexAssignment) {
    var valueVariable = new VariableDeclaration.forValue(value);
    if (setter == null) {
      helper.warnUnresolvedMethod(indexSetName, offsetForToken(token),
          isSuper: true);
    }
    var write = new SuperMethodInvocation(
        indexSetName,
        forest.castArguments(forest.arguments(
            <Expression>[indexAccess(), new VariableGet(valueVariable)],
            token)),
        setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    var dummy = new VariableDeclaration.forValue(write);
    return makeLet(
        valueVariable, makeLet(dummy, new VariableGet(valueVariable)));
  }

  @override
  Expression _makeSimpleRead() {
    if (getter == null) {
      helper.warnUnresolvedMethod(indexGetName, offsetForToken(token),
          isSuper: true);
    }
    // TODO(ahe): Use [DirectMethodInvocation] when possible.
    return new SuperMethodInvocationJudgment(indexGetName,
        forest.castArguments(forest.arguments(<Expression>[index], token)),
        interfaceTarget: getter)
      ..fileOffset = offsetForToken(token);
  }

  @override
  Expression _makeSimpleWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    if (!voidContext) return _makeWriteAndReturn(value, complexAssignment);
    if (setter == null) {
      helper.warnUnresolvedMethod(indexSetName, offsetForToken(token),
          isSuper: true);
    }
    var write = new SuperMethodInvocation(
        indexSetName,
        forest
            .castArguments(forest.arguments(<Expression>[index, value], token)),
        setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    if (getter == null) {
      helper.warnUnresolvedMethod(indexGetName, offsetForToken(token),
          isSuper: true);
    }
    var read = new SuperMethodInvocation(
        indexGetName,
        forest.castArguments(
            forest.arguments(<Expression>[indexAccess()], token)),
        getter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.read = read;
    return read;
  }

  @override
  Expression _makeWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    if (!voidContext) return _makeWriteAndReturn(value, complexAssignment);
    if (setter == null) {
      helper.warnUnresolvedMethod(indexSetName, offsetForToken(token),
          isSuper: true);
    }
    var write = new SuperMethodInvocation(
        indexSetName,
        forest.castArguments(
            forest.arguments(<Expression>[indexAccess(), value], token)),
        setter)
      ..fileOffset = offsetForToken(token);
    complexAssignment?.write = write;
    return write;
  }

  @override
  Expression _finish(
      Expression body, ComplexAssignmentJudgment complexAssignment) {
    return super._finish(
        makeLet(indexVariable, body)..fileOffset = offsetForToken(token),
        complexAssignment);
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    return helper.buildMethodInvocation(
        buildSimpleRead(), callName, arguments, offset,
        isImplicitCall: true);
  }

  @override
  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) =>
      shadow.SyntheticWrapper.wrapIndexAssignment(null, index, rhs,
          isSuper: true);

  @override
  void printOn(StringSink sink) {
    NameSystem syntheticNames = new NameSystem();
    sink.write(", index: ");
    printNodeOn(index, sink, syntheticNames: syntheticNames);
    sink.write(", getter: ");
    printQualifiedNameOn(getter, sink, syntheticNames: syntheticNames);
    sink.write(", setter: ");
    printQualifiedNameOn(setter, sink, syntheticNames: syntheticNames);
    sink.write(", indexVariable: ");
    printNodeOn(indexVariable, sink, syntheticNames: syntheticNames);
  }
}

class KernelStaticAccessGenerator extends KernelGenerator
    with StaticAccessGenerator {
  @override
  final Member readTarget;

  final Member writeTarget;

  KernelStaticAccessGenerator(ExpressionGeneratorHelper helper, Token token,
      this.readTarget, this.writeTarget)
      : assert(readTarget != null || writeTarget != null),
        super(helper, token);

  @override
  String get plainNameForRead => (readTarget ?? writeTarget).name.name;

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    Expression read;
    if (readTarget == null) {
      read = makeInvalidRead();
      if (complexAssignment != null) {
        read = helper.desugarSyntheticExpression(read);
      }
    } else {
      read = helper.makeStaticGet(readTarget, token);
    }
    complexAssignment?.read = read;
    return read;
  }

  @override
  Expression _makeWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    Expression write;
    if (writeTarget == null) {
      write = makeInvalidWrite(value);
      if (complexAssignment != null) {
        write = helper.desugarSyntheticExpression(write);
      }
    } else {
      write = new StaticSet(writeTarget, value);
    }
    complexAssignment?.write = write;
    write.fileOffset = offsetForToken(token);
    return write;
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    if (helper.constantContext != ConstantContext.none &&
        !helper.isIdentical(readTarget)) {
      return helper.buildProblem(
          templateNotConstantExpression.withArguments('Method invocation'),
          offset,
          readTarget?.name?.name?.length ?? 0);
    }
    if (readTarget == null || isFieldOrGetter(readTarget)) {
      return helper.buildMethodInvocation(buildSimpleRead(), callName,
          arguments, offset + (readTarget?.name?.name?.length ?? 0),
          // This isn't a constant expression, but we have checked if a
          // constant expression error should be emitted already.
          isConstantExpression: true,
          isImplicitCall: true);
    } else {
      return helper.buildStaticInvocation(readTarget, arguments,
          charOffset: offset);
    }
  }

  @override
  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) =>
      shadow.SyntheticWrapper.wrapStaticAssignment(rhs);

  @override
  void printOn(StringSink sink) {
    NameSystem syntheticNames = new NameSystem();
    sink.write(", readTarget: ");
    printQualifiedNameOn(readTarget, sink, syntheticNames: syntheticNames);
    sink.write(", writeTarget: ");
    printQualifiedNameOn(writeTarget, sink, syntheticNames: syntheticNames);
  }
}

class KernelLoadLibraryGenerator extends KernelGenerator
    with LoadLibraryGenerator {
  final LoadLibraryBuilder builder;

  KernelLoadLibraryGenerator(
      ExpressionGeneratorHelper helper, Token token, this.builder)
      : super(helper, token);

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    builder.importDependency.targetLibrary;
    var read = new LoadLibraryTearOffJudgment(
        builder.importDependency, builder.createTearoffMethod(helper.forest))
      ..fileOffset = offsetForToken(token);
    complexAssignment?.read = read;
    return read;
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    if (forest.argumentsPositional(arguments).length > 0 ||
        forest.argumentsNamed(arguments).length > 0) {
      helper.addProblemErrorIfConst(
          messageLoadLibraryTakesNoArguments, offset, 'loadLibrary'.length);
    }
    return builder.createLoadLibrary(offset, forest, arguments);
  }

  @override
  void printOn(StringSink sink) {
    sink.write(", builder: ");
    sink.write(builder);
  }
}

class KernelDeferredAccessGenerator extends KernelGenerator
    with DeferredAccessGenerator {
  @override
  final KernelPrefixUseGenerator prefixGenerator;

  @override
  final KernelGenerator suffixGenerator;

  KernelDeferredAccessGenerator(ExpressionGeneratorHelper helper, Token token,
      this.prefixGenerator, this.suffixGenerator)
      : super(helper, token);

  @override
  Expression _makeSimpleRead() {
    return helper.wrapInDeferredCheck(suffixGenerator._makeSimpleRead(),
        prefixGenerator.prefix, token.charOffset);
  }

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    return helper.wrapInDeferredCheck(
        suffixGenerator._makeRead(complexAssignment),
        prefixGenerator.prefix,
        token.charOffset);
  }

  @override
  Expression _makeWrite(Expression value, bool voidContext,
      ComplexAssignmentJudgment complexAssignment) {
    return helper.wrapInDeferredCheck(
        suffixGenerator._makeWrite(value, voidContext, complexAssignment),
        prefixGenerator.prefix,
        token.charOffset);
  }

  @override
  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) =>
      shadow.SyntheticWrapper.wrapStaticAssignment(rhs);
}

class KernelTypeUseGenerator extends KernelReadOnlyAccessGenerator
    with TypeUseGenerator {
  @override
  final TypeDeclarationBuilder declaration;

  KernelTypeUseGenerator(ExpressionGeneratorHelper helper, Token token,
      this.declaration, String plainNameForRead)
      : super(helper, token, null, plainNameForRead);

  @override
  Expression get expression {
    if (super.expression == null) {
      int offset = offsetForToken(token);
      if (declaration is KernelInvalidTypeBuilder) {
        KernelInvalidTypeBuilder declaration = this.declaration;
        helper.addProblemErrorIfConst(
            declaration.message.messageObject, offset, token.length);
        super.expression = helper.wrapSyntheticExpression(
            forest.throwExpression(
                null, forest.literalString(declaration.message.message, token))
              ..fileOffset = offset,
            offset);
      } else {
        super.expression = forest.literalType(
            helper.buildDartType(
                new UnresolvedType<KernelTypeBuilder>(
                    buildTypeWithResolvedArguments(null), offset, uri),
                nonInstanceAccessIsError: true),
            token);
      }
    }
    return super.expression;
  }

  @override
  Expression makeInvalidWrite(Expression value) {
    return helper.wrapSyntheticExpression(
        helper.throwNoSuchMethodError(
            forest.literalNull(token),
            plainNameForRead,
            forest.arguments(<Expression>[value], null)
              ..fileOffset = value.fileOffset,
            offsetForToken(token),
            isSetter: true),
        offsetForToken(token));
  }

  @override
  buildPropertyAccess(
      IncompleteSendGenerator send, int operatorOffset, bool isNullAware) {
    // `SomeType?.toString` is the same as `SomeType.toString`, not
    // `(SomeType).toString`.
    isNullAware = false;

    Name name = send.name;
    Arguments arguments = send.arguments;

    if (declaration is KernelClassBuilder) {
      KernelClassBuilder declaration = this.declaration;
      Declaration member = declaration.findStaticBuilder(
          name.name, offsetForToken(send.token), uri, helper.library);

      Generator generator;
      if (member == null) {
        // If we find a setter, [member] is an [AccessErrorBuilder], not null.
        if (send is IncompletePropertyAccessGenerator) {
          generator = new UnresolvedNameGenerator(helper, send.token, name);
        } else {
          return helper.buildConstructorInvocation(
              declaration,
              send.token,
              send.token,
              arguments,
              name.name,
              null,
              token.charOffset,
              Constness.implicit);
        }
      } else if (member is AmbiguousBuilder) {
        return helper.buildProblem(
            member.message, member.charOffset, name.name.length);
      } else {
        Declaration setter;
        if (member.isSetter) {
          setter = member;
        } else if (member.isGetter) {
          setter = declaration.findStaticBuilder(
              name.name, offsetForToken(token), uri, helper.library,
              isSetter: true);
        } else if (member.isField && !member.isFinal) {
          setter = member;
        }
        generator = new StaticAccessGenerator.fromBuilder(
            helper, member, send.token, setter);
      }

      return arguments == null
          ? generator
          : generator.doInvocation(offsetForToken(send.token), arguments);
    } else {
      return super.buildPropertyAccess(send, operatorOffset, isNullAware);
    }
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    return helper.buildConstructorInvocation(declaration, token, token,
        arguments, "", null, token.charOffset, Constness.implicit);
  }
}

class KernelReadOnlyAccessGenerator extends KernelGenerator
    with ReadOnlyAccessGenerator {
  @override
  final String plainNameForRead;

  Expression expression;

  VariableDeclaration value;

  KernelReadOnlyAccessGenerator(ExpressionGeneratorHelper helper, Token token,
      this.expression, this.plainNameForRead)
      : super(helper, token);

  @override
  Expression _makeSimpleRead() => expression;

  @override
  Expression _makeRead(ComplexAssignmentJudgment complexAssignment) {
    value ??= new VariableDeclaration.forValue(expression);
    return new VariableGet(value);
  }

  @override
  Expression _finish(
          Expression body, ComplexAssignmentJudgment complexAssignment) =>
      super._finish(makeLet(value, body), complexAssignment);

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    return helper.buildMethodInvocation(buildSimpleRead(), callName, arguments,
        adjustForImplicitCall(plainNameForRead, offset),
        isImplicitCall: true);
  }

  @override
  void printOn(StringSink sink) {
    NameSystem syntheticNames = new NameSystem();
    sink.write(", expression: ");
    printNodeOn(expression, sink, syntheticNames: syntheticNames);
    sink.write(", plainNameForRead: ");
    sink.write(plainNameForRead);
    sink.write(", value: ");
    printNodeOn(value, sink, syntheticNames: syntheticNames);
  }
}

class KernelUnresolvedNameGenerator extends KernelGenerator
    with ErroneousExpressionGenerator, UnresolvedNameGenerator {
  @override
  final Name name;

  KernelUnresolvedNameGenerator(
      ExpressionGeneratorHelper helper, Token token, this.name)
      : super(helper, token);

  @override
  Expression buildAssignment(Expression value, {bool voidContext: false}) {
    return _buildUnresolvedVariableAssignment(false, value);
  }

  @override
  Expression buildCompoundAssignment(Name binaryOperator, Expression value,
      {int offset: TreeNode.noOffset,
      bool voidContext: false,
      Procedure interfaceTarget,
      bool isPreIncDec: false,
      bool isPostIncDec: false}) {
    return _buildUnresolvedVariableAssignment(true, value);
  }

  @override
  Expression buildSimpleRead() {
    return buildError(forest.argumentsEmpty(token), isGetter: true)
      ..fileOffset = token.charOffset;
  }

  @override
  void printOn(StringSink sink) {
    sink.write(", name: ");
    sink.write(name.name);
  }

  Expression _buildUnresolvedVariableAssignment(
      bool isCompound, Expression value) {
    return helper.wrapUnresolvedVariableAssignment(
        helper.desugarSyntheticExpression(buildError(
            forest.arguments(<Expression>[value], token),
            isSetter: true)),
        isCompound,
        value,
        token.charOffset);
  }
}

class KernelUnlinkedGenerator extends KernelGenerator with UnlinkedGenerator {
  @override
  final UnlinkedDeclaration declaration;

  final Expression receiver;

  final Name name;

  KernelUnlinkedGenerator(
      ExpressionGeneratorHelper helper, Token token, this.declaration)
      : name = new Name(declaration.name, helper.library.target),
        receiver = new InvalidExpression(declaration.name)
          ..fileOffset = offsetForToken(token),
        super(helper, token);

  @override
  Expression buildAssignment(Expression value, {bool voidContext}) {
    return new PropertySet(receiver, name, value)
      ..fileOffset = offsetForToken(token);
  }

  @override
  Expression buildSimpleRead() {
    return new PropertyGet(receiver, name)..fileOffset = offsetForToken(token);
  }

  @override
  Expression doInvocation(int offset, Arguments arguments) {
    return unsupported("doInvocation", offset, uri);
  }
}

abstract class KernelContextAwareGenerator extends KernelGenerator
    with ContextAwareGenerator {
  @override
  final Generator generator;

  KernelContextAwareGenerator(
      ExpressionGeneratorHelper helper, Token token, this.generator)
      : super(helper, token);
}

class KernelDelayedAssignment extends KernelContextAwareGenerator
    with DelayedAssignment {
  @override
  final Expression value;

  @override
  String assignmentOperator;

  KernelDelayedAssignment(ExpressionGeneratorHelper helper, Token token,
      Generator generator, this.value, this.assignmentOperator)
      : super(helper, token, generator);

  @override
  void printOn(StringSink sink) {
    sink.write(", value: ");
    printNodeOn(value, sink);
    sink.write(", assignmentOperator: ");
    sink.write(assignmentOperator);
  }
}

class KernelDelayedPostfixIncrement extends KernelContextAwareGenerator
    with DelayedPostfixIncrement {
  @override
  final Name binaryOperator;

  @override
  final Procedure interfaceTarget;

  KernelDelayedPostfixIncrement(ExpressionGeneratorHelper helper, Token token,
      Generator generator, this.binaryOperator, this.interfaceTarget)
      : super(helper, token, generator);
}

class KernelPrefixUseGenerator extends KernelGenerator with PrefixUseGenerator {
  final PrefixBuilder prefix;

  KernelPrefixUseGenerator(
      ExpressionGeneratorHelper helper, Token token, this.prefix)
      : super(helper, token);
}

class KernelUnexpectedQualifiedUseGenerator extends KernelGenerator
    with UnexpectedQualifiedUseGenerator {
  @override
  final KernelGenerator prefixGenerator;

  @override
  final bool isUnresolved;

  KernelUnexpectedQualifiedUseGenerator(ExpressionGeneratorHelper helper,
      Token token, this.prefixGenerator, this.isUnresolved)
      : super(helper, token);
}

class KernelParserErrorGenerator extends KernelGenerator
    with ParserErrorGenerator {
  @override
  final Message message;

  KernelParserErrorGenerator(
      ExpressionGeneratorHelper helper, Token token, this.message)
      : super(helper, token);
}

Expression makeLet(VariableDeclaration variable, Expression body) {
  if (variable == null) return body;
  return new Let(variable, body);
}

Expression makeBinary(Expression left, Name operator, Procedure interfaceTarget,
    Expression right, ExpressionGeneratorHelper helper,
    {int offset: TreeNode.noOffset}) {
  return new MethodInvocationJudgment(
      left,
      operator,
      helper.forest
          .castArguments(helper.forest.arguments(<Expression>[right], null))
            ..fileOffset = offset,
      interfaceTarget: interfaceTarget)
    ..fileOffset = offset;
}

Expression buildIsNull(
    Expression value, int offset, ExpressionGeneratorHelper helper) {
  return makeBinary(value, equalsName, null,
      helper.forest.literalNull(null)..fileOffset = offset, helper,
      offset: offset);
}

VariableDeclaration makeOrReuseVariable(Expression value) {
  // TODO: Devise a way to remember if a variable declaration was reused
  // or is fresh (hence needs a let binding).
  return new VariableDeclaration.forValue(value);
}

int adjustForImplicitCall(String name, int offset) {
  // Normally the offset is at the start of the token, but in this case,
  // because we insert a '.call', we want it at the end instead.
  return offset + (name?.length ?? 0);
}

bool isFieldOrGetter(Member member) {
  return member is Field || (member is Procedure && member.isGetter);
}