closure conversion: Support closures in initializers

pkg/kernel/lib/transformations/closure/rewriter.dart

+// Copyright (c) 2017, 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 kernel.transformations.closure.rewriter;
+
+import '../../ast.dart';
+import 'converter.dart' show ClosureConverter;
+
+/// Used by the [Context] to initialize and update the context variable
+/// used to capture the variables closed over by functions.
+abstract class AstRewriter {
+  /// The declared variable that holds the context.
+  VariableDeclaration contextDeclaration;
+
+  /// The expression used to initialize the size of the context stored in
+  /// [contextDeclaration]. This expression is modified when the context is
+  /// extended.
+  IntLiteral contextSize;
+
+  /// Creates a new [AstRewriter] for a (nested) [Block].
+  BlockRewriter forNestedBlock(Block block);
+
+  /// Inserts an allocation of a context and initializes [contextDeclaration]
+  /// and [contextSize].
+  void insertContextDeclaration(Class contextClass, Expression accessParent);
+
+  /// Inserts an expression or statement that extends the context, where
+  /// [arguments] holds a pair of the new index and the initial value.
+  void insertExtendContext(Expression accessContext, Arguments arguments);
+
+  void _createDeclaration(Class contextClass) {
+    assert(contextDeclaration == null && contextSize == null);
+
+    contextSize = new IntLiteral(0);
+    contextDeclaration = new VariableDeclaration.forValue(
+        new ConstructorInvocation(contextClass.constructors.first,
+            new Arguments(<Expression>[contextSize])),
+        type: new InterfaceType(contextClass));
+    contextDeclaration.name = "#context";
+  }
+}
+
+/// Adds a local variable for the context and adds update [Statement]s to the
+/// current block.
+class BlockRewriter extends AstRewriter {
+  Block _currentBlock;
+  int _insertionIndex;
+
+  BlockRewriter(this._currentBlock) : _insertionIndex = 0;
+
+  BlockRewriter forNestedBlock(Block block) {
+    return _currentBlock != block ? new BlockRewriter(block) : this;
+  }
+
+  void transformStatements(Block block, ClosureConverter converter) {
+    while (_insertionIndex < _currentBlock.statements.length) {
+      var original = _currentBlock.statements[_insertionIndex];
+      var transformed = original.accept(converter);
+      assert(_currentBlock.statements[_insertionIndex] == original);
+      if (transformed == null) {
+        _currentBlock.statements.removeAt(_insertionIndex);
+      } else {
+        _currentBlock.statements[_insertionIndex++] = transformed;
+        transformed.parent = _currentBlock;
+      }
+    }
+  }
+
+  void _insertStatement(Statement statement) {
+    _currentBlock.statements.insert(_insertionIndex++, statement);
+    statement.parent = _currentBlock;
+  }
+
+  void insertContextDeclaration(Class contextClass, Expression accessParent) {
+    _createDeclaration(contextClass);
+    _insertStatement(contextDeclaration);
+    _insertStatement(new ExpressionStatement(new PropertySet(
+        new VariableGet(contextDeclaration),
+        new Name('parent'),
+        accessParent)));
+  }
+
+  void insertExtendContext(Expression accessContext, Arguments arguments) {
+    _insertStatement(new ExpressionStatement(
+        new MethodInvocation(accessContext, new Name('[]='), arguments)));
+  }
+}
+
+/// Creates and updates the context as [Let] bindings around the initializer
+/// expression.
+class InitializerRewriter extends AstRewriter {
+  final Expression initializingExpression;
+
+  InitializerRewriter(this.initializingExpression) {
+    assert(initializingExpression.parent is FieldInitializer);
+  }
+
+  @override
+  BlockRewriter forNestedBlock(Block block) {
+    return new BlockRewriter(block);
+  }
+
+  @override
+  void insertContextDeclaration(Class contextClass, Expression accessParent) {
+    _createDeclaration(contextClass);
+    FieldInitializer parent = initializingExpression.parent;
+    Let binding = new Let(contextDeclaration, initializingExpression);
+    initializingExpression.parent = binding;
+    parent.value = binding;
+    binding.parent = parent;
+  }
+
+  @override
+  void insertExtendContext(Expression accessContext, Arguments arguments) {
+    Expression extendContext =
+        new MethodInvocation(accessContext, new Name('[]='), arguments);
+    Let parent = initializingExpression.parent;
+    Let binding = new Let(
+        new VariableDeclaration(null, initializer: extendContext),
+        initializingExpression);
+    parent.body = binding;
+    binding.parent = parent;
+  }
+}