LibJS: Implement parsing and executing for-await-of loops

Userland/Libraries/LibJS/Tests/loops/for-await-of.js

@@ -0,0 +1,71 @@
+describe("basic behavior", () => {
+    test("empty array", () => {
+        var enteredFunction = false;
+        var rejected = false;
+        async function f() {
+            enteredFunction = true;
+            for await (const v of []) {
+                expect().fail("Should not enter loop");
+            }
+        }
+
+        f().then(
+            () => {
+                expect(enteredFunction).toBeTrue();
+            },
+            () => {
+                rejected = true;
+            }
+        );
+        runQueuedPromiseJobs();
+        expect(enteredFunction).toBeTrue();
+        expect(rejected).toBeFalse();
+    });
+
+    test("sync iterator", () => {
+        var loopIterations = 0;
+        var rejected = false;
+        async function f() {
+            for await (const v of [1]) {
+                expect(v).toBe(1);
+                loopIterations++;
+            }
+        }
+
+        f().then(
+            () => {
+                expect(loopIterations).toBe(1);
+            },
+            () => {
+                rejected = true;
+            }
+        );
+        runQueuedPromiseJobs();
+        expect(loopIterations).toBe(1);
+        expect(rejected).toBeFalse();
+    });
+});
+
+describe("only allowed in async functions", () => {
+    test("async functions", () => {
+        expect("async function foo() { for await (const v of []) return v; }").toEval();
+        expect("(async function () { for await (const v of []) return v; })").toEval();
+        expect("async () => { for await (const v of []) return v; }").toEval();
+    });
+
+    test("regular functions", () => {
+        expect("function foo() { for await (const v of []) return v; }").not.toEval();
+        expect("(function () { for await (const v of []) return v; })").not.toEval();
+        expect("() => { for await (const v of []) return v; }").not.toEval();
+    });
+
+    test("generator functions", () => {
+        expect("function* foo() { for await (const v of []) return v; }").not.toEval();
+        expect("(function* () { for await (const v of []) return v; })").not.toEval();
+    });
+
+    test("async genrator functions", () => {
+        expect("async function* foo() { for await (const v of []) yield v; }").toEval();
+        expect("(async function* () { for await (const v of []) yield v; })").toEval();
+    });
+});