Preserve empty for...of loops

src/ast/nodes/ForOfStatement.ts

@@ -1,6 +1,6 @@
 import MagicString from 'magic-string';
 import { NO_SEMICOLON, RenderOptions } from '../../utils/renderHelpers';
-import { ExecutionPathOptions } from '../ExecutionPathOptions';
+// import { ExecutionPathOptions } from '../ExecutionPathOptions';
 import BlockScope from '../scopes/BlockScope';
 import Scope from '../scopes/Scope';
 import { EMPTY_PATH } from '../values';
@@ -27,14 +27,17 @@ export default class ForOfStatement extends StatementBase {
 		this.scope = new BlockScope(parentScope);
 	}
 
-	hasEffects(options: ExecutionPathOptions): boolean {
-		return (
-			(this.left &&
-				(this.left.hasEffects(options) ||
-					this.left.hasEffectsWhenAssignedAtPath(EMPTY_PATH, options))) ||
-			(this.right && this.right.hasEffects(options)) ||
-			this.body.hasEffects(options.setIgnoreBreakStatements())
-		);
+	hasEffects(/* options: ExecutionPathOptions */): boolean {
+		// Placeholder until proper Symbol.Iterator support
+		return true;
+
+		// return (
+		// 	(this.left &&
+		// 		(this.left.hasEffects(options) ||
+		// 			this.left.hasEffectsWhenAssignedAtPath(EMPTY_PATH, options))) ||
+		// 	(this.right && this.right.hasEffects(options)) ||
+		// 	this.body.hasEffects(options.setIgnoreBreakStatements())
+		// );
 	}
 
 	include(includeChildrenRecursively: IncludeChildren) {

test/function/samples/preserve-for-of-iterable/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'preserves for...of loops'
+};

test/function/samples/preserve-for-of-iterable/iterables.js

@@ -0,0 +1,18 @@
+export const zeroToFive = {
+    [Symbol.iterator]() {
+        return {
+            current: 0,
+            last: 5,
+            next() {
+                const ret = this.current < this.last
+                    ? { done: false, value: this.current++ }
+                    : { done: true };
+
+                // assert later
+                global.foo = this.current;
+
+                return ret;
+            }
+        };
+    }
+};

test/function/samples/preserve-for-of-iterable/loops.js

@@ -0,0 +1,19 @@
+export const awaitable = async (iterable) => {
+	for await (const value of iterable) {
+	}
+}
+
+// This is equivalent to the above 'awaitable' function.
+export const equivalent = async (iterable) => {
+	const iterator = iterable[Symbol.asyncIterator]()
+  let { done } = await iterator.next()
+  while (!done) {
+    ({ done } = await iterator.next())
+  }
+
+}
+
+export const iterate = iterable => {
+	for (const value of iterable) {
+	}
+}

test/function/samples/preserve-for-of-iterable/main.js

@@ -0,0 +1,6 @@
+import { zeroToFive } from './iterables';
+import { iterate } from './loops';
+
+assert.equal(global.foo, undefined);
+iterate(zeroToFive);
+assert.equal(global.foo, 5);