feat(transpiler): Transform for..of to Dart as for..in

fixes #53

tools/transpiler/spec/fixtures/facade.dart

@@ -1,3 +1,16 @@
+import 'dart:collection';
+
 class MapWrapper {
 
-}
+}
+
+/**
+ * Generic iterable class to test for-of.  Provides iteration of the given list.
+ */
+class IterableList extends IterableBase {
+  List values;
+  IterableList(values) {
+    this.values = values;
+  }
+  Iterator get iterator => values.iterator;
+}

tools/transpiler/spec/fixtures/facade.es6

@@ -1,3 +1,18 @@
 export class MapWrapper {
 
-}
+}
+
+/**
+ * Generic iterable class to test for-of.  Provides iteration of the given array.
+ */
+export class IterableList {
+  constructor(values) {
+    this.values = values;
+  }
+
+  *[Symbol.iterator]() {
+    for (var value of this.values) {
+      yield value;
+    }
+  }
+}

tools/transpiler/spec/for_of_spec.js

@@ -0,0 +1,51 @@
+import {describe, it, expect} from 'test_lib/test_lib';
+import {ListWrapper, MapWrapper} from 'facade/collection';
+import {IterableList} from './fixtures/facade';
+
+export function main() {
+  describe('for..of', function() {
+    it('should iterate iterable', function() {
+      var values = ['a', 'b', 'c'];
+      var result = ListWrapper.create();
+      for (var value of new IterableList(values)) {
+        ListWrapper.push(result, value);
+      }
+      expect(result).toEqual(values);
+    });
+
+    it('should iterate iterable without var declaration list', function() {
+      var values = ['a', 'b', 'c'];
+      var result = ListWrapper.create();
+      var value;
+      for (value of new IterableList(values)) {
+        ListWrapper.push(result, value);
+      }
+      expect(value).toEqual('c');
+      expect(result).toEqual(values);
+    });
+
+    it('should iterate maps', function() {
+      var values = [['a', 1], ['b', 2], ['c', 3]];
+      var result = ListWrapper.create();
+      var map = MapWrapper.createFromPairs(values);
+      for (var [key, value] of MapWrapper.iterable(map)) {
+        ListWrapper.push(result, [key, value]);
+      }
+      expect(result).toEqual(values);
+    });
+
+    it('should iterate maps without var declaration list', function() {
+      var values = [['a', 1], ['b', 2], ['c', 3]];
+      var result = ListWrapper.create();
+      var map = MapWrapper.createFromPairs(values);
+      var key, value;
+      for ([key, value] of MapWrapper.iterable(map)) {
+        ListWrapper.push(result, [key, value]);
+      }
+      expect(key).toEqual('c');
+      expect(value).toEqual(3);
+      expect(result).toEqual(values);
+    });
+  });
+}
+

tools/transpiler/src/codegeneration/DartTransformer.js

@@ -9,6 +9,8 @@ import {MultiVarTransformer} from './MultiVarTransformer';
 import {StrictEqualityTransformer} from './StrictEqualityTransformer';
 import {NamedParamsTransformer} from './NamedParamsTransformer';
 import {ExportTransformer} from './ExportTransformer';
+import {ForOfTransformer} from './ForOfTransformer';
+import {DestructuringTransformer} from './DestructuringTransformer';
 
 /**
  * Transforms ES6 + annotations to Dart code.
@@ -30,5 +32,7 @@ export class DartTransformer extends MultiTransformer {
     append(StrictEqualityTransformer);
     append(ClassTransformer);
     append(ExportTransformer);
+    append(ForOfTransformer);
+    append(DestructuringTransformer);
   }
 }

tools/transpiler/src/codegeneration/DestructuringTransformer.js

@@ -0,0 +1,41 @@
+import {
+  COMMA_EXPRESSION,
+  EXPRESSION_STATEMENT
+} from 'traceur/src/syntax/trees/ParseTreeType';
+
+import {
+  DestructuringTransformer as TraceurDestructuringTransformer
+} from 'traceur/src/codegeneration/DestructuringTransformer';
+
+import {
+  createExpressionStatement
+} from 'traceur/src/codegeneration/ParseTreeFactory';
+
+export class DestructuringTransformer extends TraceurDestructuringTransformer {
+  /**
+   * Overrides formal parameters to skip processing since they are already handled
+   * by the NamedParamsTransformer.
+   */
+  transformFormalParameter(tree) {
+    return tree;
+  }
+
+  /**
+   * Converts the comma expressions created by Traceur into multiple statements.
+   */
+  desugarBinding_(bindingTree, statements, declarationType) {
+    var binding = super.desugarBinding_(bindingTree, statements, declarationType);
+    for (var i = 0; i < statements.length; i++) {
+      if (statements[i].type === EXPRESSION_STATEMENT &&
+          statements[i].expression.type === COMMA_EXPRESSION) {
+        let expression = statements[i].expression;
+        let expressionStatements = expression.expressions.map(e => {
+          return createExpressionStatement(e);
+        });
+
+        statements.splice(i, 1, ...expressionStatements);
+      }
+    }
+    return binding;
+  }
+}

tools/transpiler/src/codegeneration/ForOfTransformer.js

@@ -0,0 +1,16 @@
+import {ParseTreeTransformer} from 'traceur/src/codegeneration/ParseTreeTransformer';
+import {ForInStatement} from 'traceur/src/syntax/trees/ParseTrees';
+
+/**
+ * Transforms for-of into for-in.
+ */
+export class ForOfTransformer extends ParseTreeTransformer {
+  /**
+   * @param {ForOfStatement} tree
+   * @return {ParseTree}
+   */
+  transformForOfStatement(original) {
+    var tree = super.transformForOfStatement(original);
+    return new ForInStatement(tree.location, tree.initializer, tree.collection, tree.body);
+  }
+}