init rhs of for-in loop head with correct scope - fixes #1480

src/ast/nodes/ForInStatement.js

@@ -6,18 +6,18 @@ import { STRING } from '../values.js';
 export default class ForInStatement extends Statement {
 	initialiseChildren () {
 		this.left.initialise( this.scope );
-		this.right.initialise( this.scope );
+		this.right.initialise( this.scope.parent );
 		this.body.initialiseAndReplaceScope ?
 			this.body.initialiseAndReplaceScope( this.scope ) :
 			this.body.initialise( this.scope );
 		assignTo( this.left, this.scope, STRING );
 	}
 
 	initialiseScope ( parentScope ) {
-		this.scope = new Scope( {
+		this.scope = new Scope({
 			parent: parentScope,
 			isBlockScope: true,
 			isLexicalBoundary: false
-		} );
+		});
 	}
 }

test/function/samples/for-loop-head-dependencies/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'uses parent scope for right-hand-side in for-in statement (#1480)'
+};

test/function/samples/for-loop-head-dependencies/main.js

@@ -0,0 +1,12 @@
+function foo() {
+	return ['x'];
+}
+
+const result = [];
+
+for (let i in foo()) {
+	const foo = i;
+	result.push(foo);
+}
+
+assert.deepEqual(result, [0]);