Await each value of for await over an untyped array

A JavaScript array literal that mixes promises and plain values lowers as
a checked-dynamic value, and for await over it took the synchronous
iteration path, binding the promises themselves. It now takes the async
mode of the checked-dynamic loop, which awaits each value.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/compiler/src/frontend/lowering/lower-stmts.ts

@@ -9480,9 +9480,11 @@ export function lowerForOf(lowerer: Lowerer, stmt: ts.ForOfStatement): IrStmt {
 
     // A CHECKED-DYNAMIC iterable (`unknown[]`, the collapsed
     // `(string | object)[]`, JSON-parsed values): a checked IteratorRecord
-    // binds each yielded dyn value.
+    // binds each yielded dyn value. Under `for await` (a JavaScript array
+    // literal mixing promises and plain values) the async-from-sync rules
+    // await each value.
     if (iterable.type.kind === "dyn") {
-      return lowerForOfDyn(lowerer, stmt, iterable, labels);
+      return lowerForOfDyn(lowerer, stmt, iterable, labels, stmt.awaitModifier !== undefined);
     }
     if (tupleSource === null) {
       lowerer.badType(stmt.expression, lowerer.typeOf(stmt.expression));

packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6600-npm-await-mixed-array/main.ts.json

@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6600-npm-await-mixed-array/main.ts"
+ ],
+ "diags": []
+}

tests/corpus/6600-npm-await-mixed-array/main.ts

@@ -0,0 +1,6 @@
+// for await over JavaScript array literals mixing promises and plain values
+// (in a dependency): every value is awaited before the body runs, a break
+// ends the loop, and a rejected element rejects the loop at that step.
+import { run } from 'mixed-awaits';
+
+for (const line of await run()) console.log(line);

tests/corpus/6600-npm-await-mixed-array/node_modules/mixed-awaits/index.d.ts

@@ -0,0 +1 @@
+export declare function run(): Promise<string[]>;

tests/corpus/6600-npm-await-mixed-array/node_modules/mixed-awaits/index.js

@@ -0,0 +1,19 @@
+// for await over JavaScript array literals that mix promises and plain
+// values: each value is awaited, as the async-from-sync iterator does.
+'use strict';
+async function run() {
+  var out = [];
+  for await (var p of [Promise.resolve('p1'), 'p2', Promise.resolve(3)]) out.push(typeof p + ':' + p);
+  for await (let q of [1, Promise.resolve({ n: 2 }), null]) out.push(JSON.stringify(q));
+  for await (const r of ['a', Promise.resolve('b'), 'c']) {
+    if (r === 'b') break;
+    out.push('r:' + r);
+  }
+  try {
+    for await (const s of ['ok', Promise.reject(new Error('rejected element')), 'never']) out.push('s:' + s);
+  } catch (error) {
+    out.push(error.message);
+  }
+  return out;
+}
+module.exports = { run };

tests/corpus/6600-npm-await-mixed-array/node_modules/mixed-awaits/package.json

@@ -0,0 +1 @@
+{ "name": "mixed-awaits", "version": "1.0.0", "main": "index.js", "types": "index.d.ts" }