Support transpiling for-of loops with an arbitrary lhs expression as …

…the initializer

e.g.
for (this.foo of someArray) { ...

and remove an assertion that the user only passes names and name declarations in the initializer.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=201246324

src/com/google/javascript/jscomp/Es6ForOfConverter.java

@@ -18,7 +18,6 @@
 import static com.google.javascript.jscomp.Es6ToEs3Util.createType;
 import static com.google.javascript.jscomp.Es6ToEs3Util.withType;
 
-import com.google.common.base.Preconditions;
 import com.google.javascript.jscomp.parsing.parser.FeatureSet;
 import com.google.javascript.jscomp.parsing.parser.FeatureSet.Feature;
 import com.google.javascript.rhino.IR;
@@ -46,6 +45,7 @@ public final class Es6ForOfConverter implements NodeTraversal.Callback, HotSwapC
   private final JSType unknownType;
   private final JSType stringType;
   private final JSType booleanType;
+  private final DefaultNameGenerator namer;
 
   private static final String ITER_BASE = "$jscomp$iter$";
 
@@ -59,6 +59,7 @@ public Es6ForOfConverter(AbstractCompiler compiler) {
     this.unknownType = createType(addTypes, registry, JSTypeNative.UNKNOWN_TYPE);
     this.stringType = createType(addTypes, registry, JSTypeNative.STRING_TYPE);
     this.booleanType = createType(addTypes, registry, JSTypeNative.BOOLEAN_TYPE);
+    namer = new DefaultNameGenerator();
   }
 
   @Override
@@ -126,18 +127,16 @@ private void visitForOf(Node node, Node parent) {
                     IR.getprop(iterName.cloneTree(), withStringType(IR.string("next"))),
                     iteratorNextType)),
             iIterableResultType);
-    String variableName;
-    Token declType;
-    if (variable.isName()) {
-      declType = Token.NAME;
-      variableName = variable.getQualifiedName();
+    String iteratorResultName = ITER_RESULT;
+    if (NodeUtil.isNameDeclaration(variable)) {
+      iteratorResultName += variable.getFirstChild().getString();
+    } else if (variable.isName()) {
+      iteratorResultName += variable.getString();
     } else {
-      Preconditions.checkState(NodeUtil.isNameDeclaration(variable),
-          "Expected var, let, or const. Got %s", variable);
-      declType = variable.getToken();
-      variableName = variable.getFirstChild().getQualifiedName();
+      // give arbitrary lhs expressions an arbitrary name
+      iteratorResultName += namer.generateNextName();
     }
-    Node iterResult = withType(IR.name(ITER_RESULT + variableName), iIterableResultType);
+    Node iterResult = withType(IR.name(iteratorResultName), iIterableResultType);
     iterResult.makeNonIndexable();
 
     Node call = Es6ToEs3Util.makeIterator(compiler, iterable);
@@ -182,21 +181,25 @@ private void visitForOf(Node node, Node parent) {
         withType(IR.assign(iterResult.cloneTree(), getNext.cloneTree()), iIterableResultType);
 
     Node declarationOrAssign;
-    if (declType == Token.NAME) {
+    if (!NodeUtil.isNameDeclaration(variable)) {
       declarationOrAssign =
           withType(
               IR.assign(
-                  withType(IR.name(variableName).useSourceInfoFrom(variable), typeParam),
+                  withType(variable.cloneTree().setJSDocInfo(null), typeParam),
                   withType(
                       IR.getprop(iterResult.cloneTree(), withStringType(IR.string("value"))),
                       typeParam)),
               typeParam);
       declarationOrAssign.setJSDocInfo(varJSDocInfo);
       declarationOrAssign = IR.exprResult(declarationOrAssign);
     } else {
-      declarationOrAssign = new Node(
-          declType,
-          withType(IR.name(variableName).useSourceInfoFrom(variable.getFirstChild()), typeParam));
+      Token declarationType = variable.getToken(); // i.e. VAR, CONST, or LET.
+      declarationOrAssign =
+          new Node(
+                  declarationType,
+                  IR.name(variable.getFirstChild().getString())
+                      .useSourceInfoFrom(variable.getFirstChild()))
+              .setJSType(typeParam);
       declarationOrAssign.getFirstChild().addChildToBack(
               withType(
                   IR.getprop(iterResult.cloneTree(), withStringType(IR.string("value"))),

test/com/google/javascript/jscomp/Es6ForOfConverterTest.java

@@ -193,6 +193,40 @@ public void testForOfOnNonIterable() {
         TypeValidator.TYPE_MISMATCH_WARNING);
   }
 
+  public void testForOfWithQualifiedNameInitializer() {
+    // TODO(b/79532975): handle this case in the type checker and remove disableTypeCheck();
+    disableTypeCheck();
+    disableTypeInfoValidation();
+    test(
+        "var obj = {a: 0}; for (obj.a of [1,2,3]) { console.log(obj.a); }",
+        lines(
+            "var obj = {a: 0};",
+            "for (var $jscomp$iter$0 = $jscomp.makeIterator([1,2,3]),",
+            "    $jscomp$key$a = $jscomp$iter$0.next();",
+            "    !$jscomp$key$a.done; $jscomp$key$a = $jscomp$iter$0.next()) {",
+            "  obj.a = $jscomp$key$a.value;",
+            "  {",
+            "    console.log(obj.a);",
+            "  }",
+            "}"));
+  }
+
+  public void testForOfWithComplexInitializer() {
+    // TODO(b/79532975): handle this case in the type checker and remove disableTypeCheck();
+    disableTypeCheck();
+    disableTypeInfoValidation();
+    test(
+        "function f() { return {}; } for (f()['x' + 1] of [1,2,3]) {}",
+        lines(
+            "function f() { return {}; }",
+            "for (var $jscomp$iter$0 = $jscomp.makeIterator([1,2,3]),",
+            "    $jscomp$key$a = $jscomp$iter$0.next();",
+            "    !$jscomp$key$a.done; $jscomp$key$a = $jscomp$iter$0.next()) {",
+            "  f()['x' + 1] = $jscomp$key$a.value;",
+            "  {}",
+            "}"));
+  }
+
   @Override
   protected Compiler createCompiler() {
     return new NoninjectingCompiler();