pkg/front_end/lib/src/kernel/constructor_tearoff_lowering.dart

// Copyright (c) 2021, 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';
import 'package:kernel/constructor_tearoff_lowering.dart';
import 'package:kernel/type_algebra.dart';

import '../builder/library_builder.dart';
import '../source/name_scheme.dart';
import '../source/source_library_builder.dart';
import 'external_ast_helper.dart' as extern;
import 'kernel_helper.dart';

// TODO(johnniwinther): move all lowering predicates to `package:kernel`.
export 'package:kernel/constructor_tearoff_lowering.dart';

/// Creates the [Procedure] for the lowering of a generative constructor of
/// the given [name] in [compilationUnit].
///
/// If constructor tear off lowering is not enabled, `null` is returned.
Procedure? createConstructorTearOffProcedure(
  MemberName tearOffName,
  SourceLibraryBuilder compilationUnit,
  Uri fileUri,
  int fileOffset,
  Reference? reference, {
  required bool forAbstractClassOrEnumOrMixin,
  bool forceCreateLowering = false,
}) {
  if (!forAbstractClassOrEnumOrMixin &&
      (forceCreateLowering ||
          compilationUnit
              .loader
              .target
              .backendTarget
              .isConstructorTearOffLoweringEnabled)) {
    return _createTearOffProcedure(tearOffName, fileUri, fileOffset, reference);
  }
  return null;
}

/// Creates the [Procedure] for the lowering of a non-redirecting factory of
/// the given [name] in [compilationUnit].
///
/// If constructor tear off lowering is not enabled, `null` is returned.
Procedure? createFactoryTearOffProcedure(
  MemberName tearOffName,
  SourceLibraryBuilder compilationUnit,
  Uri fileUri,
  int fileOffset,
  Reference? reference, {
  bool forceCreateLowering = false,
}) {
  if (forceCreateLowering ||
      compilationUnit
          .loader
          .target
          .backendTarget
          .isFactoryTearOffLoweringEnabled) {
    return _createTearOffProcedure(tearOffName, fileUri, fileOffset, reference);
  }
  return null;
}

/// Creates the [Procedure] for the lowering of a typedef tearoff of a
/// constructor of the given [name] in with the typedef defined in
/// [libraryBuilder].
Procedure createTypedefTearOffProcedure(
  String typedefName,
  String name,
  SourceLibraryBuilder libraryBuilder,
  Uri fileUri,
  int fileOffset,
  Reference? reference,
) {
  MemberName tearOffName = new MemberName(
    libraryBuilder.libraryName,
    typedefTearOffName(typedefName, name),
  );
  return _createTearOffProcedure(tearOffName, fileUri, fileOffset, reference);
}

/// Creates the parameters and body for [tearOff] based on
/// [declarationConstructor].
/// [enclosingDeclarationTypeParameters].
///
/// The [declarationConstructor] is the origin constructor and
/// [implementationConstructor] is the augmentation constructor, if augmented,
/// otherwise it is the [declarationConstructor].
DelayedDefaultValueCloner buildConstructorTearOffProcedure({
  required Procedure tearOff,
  required Member declarationConstructor,
  required Member implementationConstructor,
  List<TypeParameter>? enclosingDeclarationTypeParameters,
  required SourceLibraryBuilder libraryBuilder,
}) {
  assert(
    declarationConstructor is Constructor ||
        (declarationConstructor is Procedure &&
            declarationConstructor.isFactory) ||
        (declarationConstructor is Procedure &&
            declarationConstructor.isStatic),
    "Unexpected constructor tear off target $declarationConstructor "
    "(${declarationConstructor.runtimeType}).",
  );
  assert(
    declarationConstructor is Constructor ||
        (declarationConstructor is Procedure &&
            declarationConstructor.isFactory) ||
        (declarationConstructor is Procedure &&
            declarationConstructor.isStatic),
    "Unexpected constructor tear off target $declarationConstructor "
    "(${declarationConstructor.runtimeType}).",
  );

  FunctionNode function = implementationConstructor.function!;

  int fileOffset = tearOff.fileOffset;

  // Generative constructors implicitly have the type parameters of the
  // enclosing class.
  // Factory constructors explicitly copy over the type parameters of the
  // enclosing class.
  List<TypeParameter> declarationTypeParameters =
      enclosingDeclarationTypeParameters ?? function.typeParameters;

  FreshTypeParameters freshTypeParameters = _createFreshTypeParameters(
    declarationTypeParameters,
    tearOff.function,
  );

  List<DartType> typeArguments = freshTypeParameters.freshTypeArguments;
  Substitution substitution = freshTypeParameters.substitution;
  DelayedDefaultValueCloner delayedDefaultValueCloner = _createParameters(
    tearOff,
    implementationConstructor,
    function,
    substitution,
    libraryBuilder,
  );
  Arguments arguments = _createArguments(tearOff, typeArguments, fileOffset);
  _createTearOffBody(tearOff, declarationConstructor, arguments);
  tearOff.function.fileOffset = tearOff.fileOffset;
  tearOff.function.fileEndOffset = tearOff.fileOffset;
  return delayedDefaultValueCloner;
}

/// Creates the parameters and body for [tearOff] for a typedef tearoff of
/// [declarationConstructor] in [enclosingTypeDeclaration] with [typeParameters]
/// as the typedef parameters and [typeArguments] as the arguments passed to the
/// [enclosingTypeDeclaration].
///
/// The [declarationConstructor] is the origin constructor and
/// [implementationConstructor] is the augmentation constructor, if augmented,
/// otherwise it is the [declarationConstructor].
DelayedDefaultValueCloner buildTypedefTearOffProcedure({
  required Procedure tearOff,
  required Member declarationConstructor,
  required Member implementationConstructor,
  required TypeDeclaration enclosingTypeDeclaration,
  required List<TypeParameter> typeParameters,
  required List<DartType> typeArguments,
  required SourceLibraryBuilder libraryBuilder,
}) {
  assert(
    declarationConstructor is Constructor ||
        (declarationConstructor is Procedure &&
            declarationConstructor.isFactory) ||
        (declarationConstructor is Procedure &&
            declarationConstructor.isStatic),
    "Unexpected constructor tear off target $declarationConstructor "
    "(${declarationConstructor.runtimeType}).",
  );
  assert(
    implementationConstructor is Constructor ||
        (implementationConstructor is Procedure &&
            implementationConstructor.isFactory) ||
        (implementationConstructor is Procedure &&
            implementationConstructor.isStatic),
    "Unexpected constructor tear off target $implementationConstructor "
    "(${declarationConstructor.runtimeType}).",
  );

  FunctionNode function = implementationConstructor.function!;

  int fileOffset = tearOff.fileOffset;

  List<TypeParameter> declarationTypeParameters;
  if (declarationConstructor is Constructor) {
    // Generative constructors implicitly have the type parameters of the
    // enclosing class.
    declarationTypeParameters = enclosingTypeDeclaration.typeParameters;
  } else {
    // Factory constructors explicitly copy over the type parameters of the
    // enclosing class.
    declarationTypeParameters = function.typeParameters;
  }

  FreshTypeParameters freshTypeParameters = _createFreshTypeParameters(
    typeParameters,
    tearOff.function,
  );

  Substitution substitution = freshTypeParameters.substitution;
  if (!substitution.isEmpty) {
    if (typeArguments.isNotEmpty) {
      // Translate [typeArgument] into the context of the synthesized procedure.
      typeArguments = new List<DartType>.generate(
        typeArguments.length,
        (int index) => substitution.substituteType(typeArguments[index]),
      );
    }
  }
  DelayedDefaultValueCloner delayedDefaultValueCloner = _createParameters(
    tearOff,
    implementationConstructor,
    function,
    Substitution.fromPairs(declarationTypeParameters, typeArguments),
    libraryBuilder,
  );
  Arguments arguments = _createArguments(tearOff, typeArguments, fileOffset);
  _createTearOffBody(tearOff, declarationConstructor, arguments);
  tearOff.function.fileOffset = tearOff.fileOffset;
  tearOff.function.fileEndOffset = tearOff.fileOffset;
  return delayedDefaultValueCloner;
}

/// Creates the parameters for the redirecting factory [tearOff] based on the
/// [declarationConstructor] declaration.
///
/// The [declarationConstructor] is the [Procedure] for the origin constructor
/// and [implementationConstructorFunctionNode] is the [FunctionNode] for the
/// implementation constructor. If the constructor is augmented, these are not
/// connected until [Builder.buildBodyNodes].
FreshTypeParameters buildRedirectingFactoryTearOffProcedureParameters({
  required Procedure tearOff,
  required Procedure implementationConstructor,
  required SourceLibraryBuilder libraryBuilder,
  List<DelayedDefaultValueCloner>? delayedDefaultValueCloners,
}) {
  FunctionNode function = implementationConstructor.function;
  FreshTypeParameters freshTypeParameters = _createFreshTypeParameters(
    function.typeParameters,
    tearOff.function,
  );
  Substitution substitution = freshTypeParameters.substitution;
  DelayedDefaultValueCloner delayedDefaultValueCloner = _createParameters(
    tearOff,
    implementationConstructor,
    function,
    substitution,
    libraryBuilder,
  );
  // Coverage-ignore(suite): Not run.
  delayedDefaultValueCloners?.add(delayedDefaultValueCloner);
  tearOff.function.fileOffset = tearOff.fileOffset;
  tearOff.function.fileEndOffset = tearOff.fileOffset;
  return freshTypeParameters;
}

/// Creates the body for the redirecting factory [tearOff] with the [target]
/// constructor and [typeArguments].
///
/// Returns the [DelayedDefaultValueCloner] object need to perform default value
/// computation.
DelayedDefaultValueCloner buildRedirectingFactoryTearOffBody(
  Procedure tearOff,
  Member target,
  List<DartType> typeArguments,
  FreshTypeParameters freshTypeParameters,
  LibraryBuilder libraryBuilder,
) {
  int fileOffset = tearOff.fileOffset;

  List<TypeParameter> typeParameters;
  if (target is Constructor) {
    typeParameters = target.enclosingClass.typeParameters;
  } else {
    typeParameters = target.function!.typeParameters;
  }

  if (!freshTypeParameters.substitution.isEmpty) {
    if (typeArguments.length != typeParameters.length) {
      // Error case: Use default types as type arguments.
      typeArguments = new List<DartType>.generate(
        typeParameters.length,
        // Coverage-ignore(suite): Not run.
        (int index) => typeParameters[index].defaultType,
      );
    }
    if (typeArguments.isNotEmpty) {
      // Translate [typeArgument] into the context of the synthesized procedure.
      typeArguments = new List<DartType>.generate(
        typeArguments.length,
        (int index) => freshTypeParameters.substitution.substituteType(
          typeArguments[index],
        ),
      );
    }
  }
  Arguments arguments = _createArguments(tearOff, typeArguments, fileOffset);
  _createTearOffBody(tearOff, target, arguments);
  return new DelayedDefaultValueCloner(
    target,
    tearOff,
    identicalSignatures: false,
    libraryBuilder: libraryBuilder,
  );
}

/// Creates the synthesized [Procedure] node for a tear off lowering by the
/// given [name].
Procedure _createTearOffProcedure(
  MemberName tearOffName,
  Uri fileUri,
  int fileOffset,
  Reference? reference,
) {
  Procedure tearOff = extern.createProcedure(
    dummyName,
    ProcedureKind.Method,
    extern.createFunctionNode(null, fileOffset: fileOffset),
    fileUri: fileUri,
    isStatic: true,
    isSynthetic: true,
    reference: reference,
    fileStartOffset: fileOffset,
    fileOffset: fileOffset,
    fileEndOffset: fileOffset,
  );
  tearOffName.attachMember(tearOff);
  return tearOff;
}

/// Creates the synthesized type parameters for a tear off lowering. The type
/// parameters are based [originalTypeParameters] and are inserted into
/// [newFunctionNode]. The created [FreshTypeParameters] is returned.
FreshTypeParameters _createFreshTypeParameters(
  List<TypeParameter> originalTypeParameters,
  FunctionNode newFunctionNode,
) {
  FreshTypeParameters freshTypeParameters;
  if (originalTypeParameters.isNotEmpty) {
    freshTypeParameters = getFreshTypeParameters(originalTypeParameters);
    List<TypeParameter> typeParameters =
        freshTypeParameters.freshTypeParameters;
    newFunctionNode.typeParameters.addAll(typeParameters);
    setParents(typeParameters, newFunctionNode);
  } else {
    freshTypeParameters = new FreshTypeParameters([], [], Substitution.empty);
  }
  return freshTypeParameters;
}

/// Creates the parameters for the [tearOff] lowering based of the parameters
/// in [constructor] and using the [substitution] to compute the parameter and
/// return types.
DelayedDefaultValueCloner _createParameters(
  Procedure tearOff,
  Member constructor,
  FunctionNode function,
  Substitution substitution,
  SourceLibraryBuilder libraryBuilder,
) {
  PositionalParameter createTearOffPositionalParameter(
    PositionalParameter constructorParameter,
  ) {
    DartType tearOffParameterType = substitution.substituteType(
      constructorParameter.type,
    );
    return extern.createPositionalParameter(
      cosmeticName: constructorParameter.cosmeticName,
      type: tearOffParameterType,
      fileOffset: constructorParameter.fileOffset,
    );
  }

  NamedParameter createTearOffNamedParameter(
    NamedParameter constructorParameter,
  ) {
    DartType tearOffParameterType = substitution.substituteType(
      constructorParameter.type,
    );
    return extern.createNamedParameter(
      parameterName: constructorParameter.parameterName,
      type: tearOffParameterType,
      isRequired: constructorParameter.isRequired,
      fileOffset: constructorParameter.fileOffset,
    );
  }

  for (PositionalParameter constructorParameter
      in function.positionalParameters) {
    PositionalParameter tearOffParameter = createTearOffPositionalParameter(
      constructorParameter,
    );
    tearOff.function.positionalParameters.add(tearOffParameter);
    tearOffParameter.parent = tearOff.function;
  }
  for (NamedParameter constructorParameter in function.namedParameters) {
    NamedParameter tearOffParameter = createTearOffNamedParameter(
      constructorParameter,
    );
    tearOff.function.namedParameters.add(tearOffParameter);
    tearOffParameter.parent = tearOff.function;
  }
  tearOff.function.returnType = substitution.substituteType(
    function.returnType,
  );
  tearOff.function.requiredParameterCount = function.requiredParameterCount;
  libraryBuilder.loader.registerTypeDependency(
    tearOff,
    new TypeDependency(
      tearOff,
      constructor,
      substitution,
      copyReturnType: true,
    ),
  );
  return new DelayedDefaultValueCloner(
    constructor,
    tearOff,
    identicalSignatures: true,
    libraryBuilder: libraryBuilder,
  );
}

/// Creates the [Arguments] for passing the parameters from [tearOff] to its
/// target, using [typeArguments] as the passed type arguments.
Arguments _createArguments(
  Procedure tearOff,
  List<DartType> typeArguments,
  int fileOffset,
) {
  List<Expression> positionalArguments = [];
  for (PositionalParameter tearOffParameter
      in tearOff.function.positionalParameters) {
    positionalArguments.add(
      extern.createVariableGet(tearOffParameter, fileOffset: fileOffset),
    );
  }
  List<NamedExpression> namedArguments = [];
  for (NamedParameter tearOffParameter in tearOff.function.namedParameters) {
    namedArguments.add(
      extern.createNamedExpression(
        tearOffParameter.cosmeticName!,
        extern.createVariableGet(tearOffParameter, fileOffset: fileOffset),
      ),
    );
  }
  Arguments arguments = extern.createArguments(
    positionalArguments,
    named: namedArguments,
    types: typeArguments,
    fileOffset: tearOff.fileOffset,
  );
  return arguments;
}

/// Creates the tear of body for [tearOff] which calls [target] with
/// [arguments].
void _createTearOffBody(Procedure tearOff, Member target, Arguments arguments) {
  assert(
    target is Constructor ||
        (target is Procedure && target.isFactory) ||
        (target is Procedure && target.isStatic),
  );
  Expression constructorInvocation;
  if (target is Constructor) {
    constructorInvocation = extern.createConstructorInvocation(
      target,
      arguments,
      fileOffset: tearOff.fileOffset,
    );
  } else {
    constructorInvocation = extern.createStaticInvocation(
      target as Procedure,
      arguments,
      fileOffset: tearOff.fileOffset,
    );
  }
  tearOff.function.registerFunctionBody(
    extern.createReturnStatement(constructorInvocation),
  );
}

/// Reverse engineered typedef tear off information.
class LoweredTypedefTearOff(
  final Procedure typedefTearOff,
  final Expression targetTearOff,
  final List<DartType> typeArguments,
) {
  /// Reverse engineers [expression] to a [LoweredTypedefTearOff] if
  /// [expression] is the encoding of a lowered typedef tear off.
  static LoweredTypedefTearOff? fromExpression(Expression expression) {
    if (expression is StaticTearOff &&
        isTypedefTearOffLowering(expression.target)) {
      Procedure typedefTearOff = expression.target;
      Statement? body = typedefTearOff.function.body;
      if (body is ReturnStatement) {
        Expression? constructorInvocation = body.expression;
        Member? target;
        List<DartType>? typeArguments;
        if (constructorInvocation is ConstructorInvocation) {
          target = constructorInvocation.target;
          typeArguments = constructorInvocation.arguments.types;
        } else if (constructorInvocation is StaticInvocation) {
          target = constructorInvocation.target;
          typeArguments = constructorInvocation.arguments.types;
        }
        if (target != null) {
          Class cls = target.enclosingClass!;
          Name tearOffName = new Name(
            constructorTearOffName(target.name.text),
            cls.enclosingLibrary,
          );
          for (Procedure procedure in cls.procedures) {
            if (procedure.name == tearOffName) {
              target = procedure;
              break;
            }
          }
          Expression targetTearOff;
          if (target is Constructor ||
              target is Procedure && target.isFactory) {
            // Coverage-ignore-block(suite): Not run.
            targetTearOff = extern.createConstructorTearOff(
              target!,
              fileOffset: expression.fileOffset,
            );
          } else {
            targetTearOff = extern.createStaticTearOff(
              target as Procedure,
              fileOffset: expression.fileOffset,
            );
          }
          return new LoweredTypedefTearOff(
            typedefTearOff,
            targetTearOff,
            typeArguments!,
          );
        }
      }
    }
    return null;
  }
}