Reassign for-in loop variable; resolves #2199

src/ast/nodes/ForInStatement.ts

@@ -1,7 +1,7 @@
 import BlockScope from '../scopes/BlockScope';
 import VariableDeclaration from './VariableDeclaration';
 import Scope from '../scopes/Scope';
-import { ExecutionPathOptions } from '../ExecutionPathOptions';
+import { ExecutionPathOptions, NEW_EXECUTION_PATH } from '../ExecutionPathOptions';
 import { PatternNode } from './shared/Pattern';
 import * as NodeType from './NodeType';
 import { ExpressionNode, Node, StatementBase, StatementNode } from './shared/Node';
@@ -19,6 +19,13 @@ export default class ForInStatement extends StatementBase {
 	right: ExpressionNode;
 	body: StatementNode;
 
+	bind() {
+		super.bind();
+		if (this.left.type !== NodeType.VariableDeclaration) {
+			this.left.reassignPath(EMPTY_PATH, NEW_EXECUTION_PATH);
+		}
+	}
+
 	createScope(parentScope: Scope) {
 		this.scope = new BlockScope({ parent: parentScope });
 	}

src/ast/nodes/ForOfStatement.ts

@@ -21,7 +21,9 @@ export default class ForOfStatement extends StatementBase {
 
 	bind() {
 		super.bind();
-		this.left.reassignPath(EMPTY_PATH, NEW_EXECUTION_PATH);
+		if (this.left.type !== NodeType.VariableDeclaration) {
+			this.left.reassignPath(EMPTY_PATH, NEW_EXECUTION_PATH);
+		}
 	}
 
 	createScope(parentScope: Scope) {

test/function/samples/for-loops-as-assignments/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'make sure for loops are counted as variable assignments (#2199)'
+};

test/function/samples/for-loops-as-assignments/main.js

@@ -0,0 +1,21 @@
+let x = false;
+let iteratedForIn = false;
+
+for (x in {key: true}) {
+	if (x === 'key') {
+		iteratedForIn = true;
+	}
+}
+
+assert.ok(iteratedForIn);
+
+let y = false;
+let iteratedForOf = false;
+
+for (y of ['key']) {
+	if (y === 'key') {
+		iteratedForOf = true;
+	}
+}
+
+assert.ok(iteratedForOf);