check LHS of ForIn/ForOfStatement for constants - closes #1630

src/babel/transformation/transformers/es6/constants.js

@@ -1,12 +1,12 @@
 import * as messages from "../../../messages";
 
-export function AssignmentExpression(node, parent, scope, file) {
-  var ids = this.getBindingIdentifiers();
+function checkPath(path, file) {
+  var ids = path.getBindingIdentifiers();
 
   for (var name in ids) {
     var id = ids[name];
 
-    var binding = scope.getBinding(name);
+    var binding = path.scope.getBinding(name);
 
     // no binding exists
     if (!binding) continue;
@@ -23,8 +23,19 @@ export function AssignmentExpression(node, parent, scope, file) {
   }
 }
 
+export function AssignmentExpression(node, parent, scope, file) {
+  checkPath(this, file);
+}
+
 export { AssignmentExpression as UpdateExpression };
 
 export function VariableDeclaration(node) {
   if (node.kind === "const") node.kind = "let";
 }
+
+export function ForXStatement(node, parent, scope, file) {
+  var left = this.get("left");
+  if (left.isIdentifier() || left.isPattern()) {
+    checkPath(left, file);
+  }
+}

src/babel/traversal/scope/index.js

@@ -46,6 +46,13 @@ var programReferenceVisitor = {
     }
   },
 
+  ForXStatement(node, parent, scope, state) {
+    var left = this.get("left");
+    if (left.isPattern() || left.isIdentifier()) {
+      scope.registerConstantViolation(left);
+    }
+  },
+
   Scopable(node, parent, scope, state) {
     for (var name in scope.bindings) {
       state.references[name] = true;

src/babel/types/alias-keys.json

@@ -44,8 +44,8 @@
   "ClassDeclaration": ["Scopable", "Class", "Statement", "Declaration"],
   "ClassExpression":  ["Scopable", "Class", "Expression"],
 
-  "ForOfStatement": ["Scopable", "Statement", "For", "Loop"],
-  "ForInStatement": ["Scopable", "Statement", "For", "Loop"],
+  "ForOfStatement": ["Scopable", "Statement", "For", "Loop", "ForXStatement"],
+  "ForInStatement": ["Scopable", "Statement", "For", "Loop", "ForXStatement"],
   "ForStatement":   ["Scopable", "Statement", "For", "Loop"],
 
   "ObjectPattern":     ["Pattern"],

test/core/fixtures/transformation/es6.constants/no-for-in/actual.js

@@ -0,0 +1,3 @@
+const MULTIPLIER = 5;
+
+for (MULTIPLIER in arr);

test/core/fixtures/transformation/es6.constants/no-for-in/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "\"MULTIPLIER\" is read-only"
+}