pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.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.

library fasta.redirecting_factory_body;

import 'package:kernel/ast.dart'
    show
        DartType,
        DynamicType,
        Expression,
        ExpressionStatement,
        FunctionNode,
        InvalidExpression,
        Let,
        Member,
        NullLiteral,
        Procedure,
        StaticGet,
        StringLiteral,
        TypeParameterType,
        VariableDeclaration;

import 'package:kernel/type_algebra.dart' show Substitution;

const String letName = "#redirecting_factory";

class RedirectingFactoryBody extends ExpressionStatement {
  RedirectingFactoryBody.internal(Expression value,
      [List<DartType> typeArguments])
      : super(new Let(new VariableDeclaration(letName, initializer: value),
            encodeTypeArguments(typeArguments)));

  RedirectingFactoryBody(Member target, [List<DartType> typeArguments])
      : this.internal(new StaticGet(target), typeArguments);

  RedirectingFactoryBody.unresolved(String name)
      : this.internal(new StringLiteral(name));

  Member get target {
    var value = getValue(expression);
    return value is StaticGet ? value.target : null;
  }

  String get unresolvedName {
    var value = getValue(expression);
    return value is StringLiteral ? value.value : null;
  }

  bool get isUnresolved => unresolvedName != null;

  List<DartType> get typeArguments {
    if (expression is Let) {
      Let bodyExpression = expression;
      if (bodyExpression.variable.name == letName) {
        return decodeTypeArguments(bodyExpression.body);
      }
    }
    return null;
  }

  static getValue(Expression expression) {
    if (expression is Let) {
      VariableDeclaration variable = expression.variable;
      if (variable.name == letName) {
        return variable.initializer;
      }
    }
    return null;
  }

  static void restoreFromDill(Procedure factory) {
    // This is a hack / work around for storing redirecting constructors in
    // dill files. See `KernelClassBuilder.addRedirectingConstructor` in
    // [kernel_class_builder.dart](kernel_class_builder.dart).
    FunctionNode function = factory.function;
    ExpressionStatement statement = function.body;
    List<DartType> typeArguments;
    if (statement.expression is Let) {
      Let expression = statement.expression;
      typeArguments = decodeTypeArguments(expression.body);
    }
    function.body = new RedirectingFactoryBody.internal(
        getValue(statement.expression), typeArguments)
      ..parent = function;
  }

  static Expression encodeTypeArguments(List<DartType> typeArguments) {
    String varNamePrefix = "#typeArg";
    Expression result = new InvalidExpression(null);
    if (typeArguments == null) {
      return result;
    }
    for (int i = typeArguments.length - 1; i >= 0; i--) {
      result = new Let(
          new VariableDeclaration("$varNamePrefix$i",
              type: typeArguments[i], initializer: new NullLiteral()),
          result);
    }
    return result;
  }

  static List<DartType> decodeTypeArguments(Expression encoded) {
    if (encoded is InvalidExpression) {
      return null;
    }
    List<DartType> result = <DartType>[];
    while (encoded is Let) {
      Let head = encoded;
      result.add(head.variable.type);
      encoded = head.body;
    }
    return result;
  }
}

RedirectingFactoryBody getRedirectingFactoryBody(Member member) {
  return member is Procedure && member.function.body is RedirectingFactoryBody
      ? member.function.body
      : null;
}

class RedirectionTarget {
  final Member target;
  final List<DartType> typeArguments;

  RedirectionTarget(this.target, this.typeArguments);
}

RedirectionTarget getRedirectionTarget(Procedure member, {bool strongMode}) {
  List<DartType> typeArguments = <DartType>[]..length =
      member.function.typeParameters.length;
  for (int i = 0; i < typeArguments.length; i++) {
    typeArguments[i] = new TypeParameterType(member.function.typeParameters[i]);
  }

  // We use the [tortoise and hare algorithm]
  // (https://en.wikipedia.org/wiki/Cycle_detection#Tortoise_and_hare) to
  // handle cycles.
  Member tortoise = member;
  RedirectingFactoryBody tortoiseBody = getRedirectingFactoryBody(tortoise);
  Member hare = tortoiseBody?.target;
  RedirectingFactoryBody hareBody = getRedirectingFactoryBody(hare);
  while (tortoise != hare) {
    if (tortoiseBody?.isUnresolved ?? true)
      return new RedirectionTarget(tortoise, typeArguments);
    Member nextTortoise = tortoiseBody.target;
    List<DartType> nextTypeArguments = tortoiseBody.typeArguments;
    if (strongMode && nextTypeArguments == null) {
      nextTypeArguments = <DartType>[];
    }

    if (strongMode || nextTypeArguments != null) {
      Substitution sub = Substitution.fromPairs(
          tortoise.function.typeParameters, typeArguments);
      typeArguments = <DartType>[]..length = nextTypeArguments.length;
      for (int i = 0; i < typeArguments.length; i++) {
        typeArguments[i] = sub.substituteType(nextTypeArguments[i]);
      }
    } else {
      // In Dart 1, we need to throw away the extra type arguments and use
      // `dynamic` in place of the missing ones.
      int typeArgumentCount = typeArguments.length;
      int nextTypeArgumentCount =
          nextTortoise.enclosingClass.typeParameters.length;
      typeArguments.length = nextTypeArgumentCount;
      for (int i = typeArgumentCount; i < nextTypeArgumentCount; i++) {
        typeArguments[i] = const DynamicType();
      }
    }

    tortoise = nextTortoise;
    tortoiseBody = getRedirectingFactoryBody(tortoise);
    hare = getRedirectingFactoryBody(hareBody?.target)?.target;
    hareBody = getRedirectingFactoryBody(hare);
  }
  return null;
}