Destructuring/default tests for generators and async functions

test/mjsunit/harmony/async-destructuring.js

Index: test/mjsunit/harmony/async-destructuring.js
diff --git a/test/mjsunit/harmony/async-destructuring.js b/test/mjsunit/harmony/async-destructuring.js
new file mode 100644
index 0000000000000000000000000000000000000000..95dbc18c7b7ed79c302df0d1d8ad42100c5ca4cc
--- /dev/null
+++ b/test/mjsunit/harmony/async-destructuring.js
@@ -0,0 +1,515 @@
+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-async-await --allow-natives-syntax
+
+function assertThrowsAsync(run, errorType, message) {
+  var actual;
+  var hadValue = false;
+  var hadError = false;
+  var promise = run();
+
+  if (typeof promise !== "object" || typeof promise.then !== "function") {
+    throw new MjsUnitAssertionError(
+        "Expected " + run.toString() +
+        " to return a Promise, but it returned " + PrettyPrint(promise));
+  }
+
+  promise.then(function(value) { hadValue = true; actual = value; },
+               function(error) { hadError = true; actual = error; });
+
+  assertFalse(hadValue || hadError);
+
+  %RunMicrotasks();
+
+  if (!hadError) {
+    throw new MjsUnitAssertionError(
+        "Expected " + run + "() to throw " + errorType.name +
+        ", but did not throw.");
+  }
+  if (!(actual instanceof errorType))
+    throw new MjsUnitAssertionError(
+        "Expected " + run + "() to throw " + errorType.name +
+        ", but threw '" + actual + "'");
+  if (message !== void 0 && actual.message !== message)
+    throw new MjsUnitAssertionError(
+        "Expected " + run + "() to throw '" + message + "', but threw '" +
+        actual.message + "'");
+};
+
+function assertEqualsAsync(expected, run, msg) {
+  var actual;
+  var hadValue = false;
+  var hadError = false;
+  var promise = run();
+
+  if (typeof promise !== "object" || typeof promise.then !== "function") {
+    throw new MjsUnitAssertionError(
+        "Expected " + run.toString() +
+        " to return a Promise, but it returned " + PrettyPrint(promise));
+  }
+
+  promise.then(function(value) { hadValue = true; actual = value; },
+               function(error) { hadError = true; actual = error; });
+
+  assertFalse(hadValue || hadError);
+
+  %RunMicrotasks();
+
+  if (hadError) throw actual;
+
+  assertTrue(
+      hadValue, "Expected '" + run.toString() + "' to produce a value");
+
+  assertEquals(expected, actual, msg);
+};
+
+(function TestDefaultEvaluationOrder() {
+  var y = 0;
+  var z = 0;
+  var w = 0;
+  async function f1(x = (y = 1)) { z = 1; await undefined; w = 1; };
+  assertEquals(0, y);
+  assertEquals(0, z);
+  assertEquals(0, w);
+  f1();
+  assertEquals(1, y);
+  assertEquals(1, z);
+  assertEquals(0, w);
+  %RunMicrotasks();
+  assertEquals(1, y);
+  assertEquals(1, z);
+  assertEquals(1, w);
+})();
+
+(function TestShadowingOfParameters() {
+  async function f1({x}) { var x = 2; return x }
+  assertEqualsAsync(2, () => f1({x: 1}));
+  async function f2({x}) { { var x = 2; } return x; }
+  assertEqualsAsync(2, () => f2({x: 1}));
+  async function f3({x}) { var y = x; var x = 2; return y; }
+  assertEqualsAsync(1, () => f3({x: 1}));
+  async function f4({x}) { { var y = x; var x = 2; } return y; }
+  assertEqualsAsync(1, () => f4({x: 1}));
+  async function f5({x}, g = () => x) { var x = 2; return g(); }
+  assertEqualsAsync(1, () => f5({x: 1}));
+  async function f6({x}, g = () => x) { { var x = 2; } return g(); }
+  assertEqualsAsync(1, () => f6({x: 1}));
+  async function f7({x}) { var g = () => x; var x = 2; return g(); }
+  assertEqualsAsync(2, () => f7({x: 1}));
+  async function f8({x}) { { var g = () => x; var x = 2; } return g(); }
+  assertEqualsAsync(2, () => f8({x: 1}));
+  async function f9({x}, g = () => eval("x")) { var x = 2; return g(); }
+  assertEqualsAsync(1, () => f9({x: 1}));
+
+  async function f10({x}, y) { var y; return y }
+  assertEqualsAsync(2, () => f10({x: 6}, 2));
+  async function f11({x}, y) { var z = y; var y = 2; return z; }
+  assertEqualsAsync(1, () => f11({x: 6}, 1));
+  async function f12(y, g = () => y) { var y = 2; return g(); }
+  assertEqualsAsync(1, () => f12(1));
+  async function f13({x}, y, [z], v) { var x, y, z; return x*y*z*v }
+  assertEqualsAsync(210, () => f13({x: 2}, 3, [5], 7));
+
+  async function f20({x}) { function x() { return 2 }; return x(); }
+  assertEqualsAsync(2, () => f20({x: 1}));
+  // Annex B 3.3 function hoisting is blocked by the conflicting x declaration
+  async function f21({x}) { { function x() { return 2 } } return x; }
+  assertEqualsAsync(1, () => f21({x: 1}));
+
+  var g1 = async ({x}) => { var x = 2; return x };
+  assertEqualsAsync(2, () => g1({x: 1}));
+  var g2 = async ({x}) => { { var x = 2; } return x; };
+  assertEqualsAsync(2, () => g2({x: 1}));
+  var g3 = async ({x}) => { var y = x; var x = 2; return y; };
+  assertEqualsAsync(1, () => g3({x: 1}));
+  var g4 = async ({x}) => { { var y = x; var x = 2; } return y; };
+  assertEqualsAsync(1, () => g4({x: 1}));
+  var g5 = async ({x}, g = () => x) => { var x = 2; return g(); };
+  assertEqualsAsync(1, () => g5({x: 1}));
+  var g6 = async ({x}, g = () => x) => { { var x = 2; } return g(); };
+  assertEqualsAsync(1, () => g6({x: 1}));
+  var g7 = async ({x}) => { var g = () => x; var x = 2; return g(); };
+  assertEqualsAsync(2, () => g7({x: 1}));
+  var g8 = async ({x}) => { { var g = () => x; var x = 2; } return g(); };
+  assertEqualsAsync(2, () => g8({x: 1}));
+  var g9 = async ({x}, g = () => eval("x")) => { var x = 2; return g(); };
+  assertEqualsAsync(1, () => g9({x: 1}));
+
+  var g10 = async ({x}, y) => { var y; return y };
+  assertEqualsAsync(2, () => g10({x: 6}, 2));
+  var g11 = async ({x}, y) => { var z = y; var y = 2; return z; };
+  assertEqualsAsync(1, () => g11({x: 6}, 1));
+  var g12 = async (y, g = () => y) => { var y = 2; return g(); };
+  assertEqualsAsync(1, () => g12(1));
+  var g13 = async ({x}, y, [z], v) => { var x, y, z; return x*y*z*v };
+  assertEqualsAsync(210, () => g13({x: 2}, 3, [5], 7));
+
+  var g20 = async ({x}) => { function x() { return 2 }; return x(); }
+  assertEqualsAsync(2, () => g20({x: 1}));
+  var g21 = async ({x}) => { { function x() { return 2 } } return x(); }
+  assertThrowsAsync(() => g21({x: 1}), TypeError);
+
+  assertThrows("'use strict'; async function f(x) { let x = 0; }", SyntaxError);
+  assertThrows("'use strict'; async function f({x}) { let x = 0; }", SyntaxError);
+  assertThrows("'use strict'; async function f(x) { const x = 0; }", SyntaxError);
+  assertThrows("'use strict'; async function f({x}) { const x = 0; }", SyntaxError);
+
+  assertThrows("'use strict'; let g = async (x) => { let x = 0; }", SyntaxError);
+  assertThrows("'use strict'; let g = async ({x}) => { let x = 0; }", SyntaxError);
+  assertThrows("'use strict'; let g = async (x) => { const x = 0; }", SyntaxError);
+  assertThrows("'use strict'; let g = async ({x}) => { const x = 0; }", SyntaxError);
+}());
+
+(function TestDefaults() {
+  async function f1(x = 1) { return x }
+  assertEqualsAsync(1, () => f1());
+  assertEqualsAsync(1, () => f1(undefined));
+  assertEqualsAsync(2, () => f1(2));
+  assertEqualsAsync(null, () => f1(null));
+
+  async function f2(x, y = x) { return x + y; }
+  assertEqualsAsync(8, () => f2(4));
+  assertEqualsAsync(8, () => f2(4, undefined));
+  assertEqualsAsync(6, () => f2(4, 2));
+
+  async function f3(x = 1, y) { return x + y; }
+  assertEqualsAsync(8, () => f3(5, 3));
+  assertEqualsAsync(3, () => f3(undefined, 2));
+  assertEqualsAsync(6, () => f3(4, 2));
+
+  async function f4(x = () => 1) { return x() }
+  assertEqualsAsync(1, () => f4());
+  assertEqualsAsync(1, () => f4(undefined));
+  assertEqualsAsync(2, () => f4(() => 2));
+  assertThrowsAsync(() => f4(null), TypeError);
+
+  async function f5(x, y = () => x) { return x + y(); }
+  assertEqualsAsync(8, () => f5(4));
+  assertEqualsAsync(8, () => f5(4, undefined));
+  assertEqualsAsync(6, () => f5(4, () => 2));
+
+  async function f6(x = {a: 1, m() { return 2 }}) { return x.a + x.m(); }
+  assertEqualsAsync(3, () => f6());
+  assertEqualsAsync(3, () => f6(undefined));
+  assertEqualsAsync(5, () => f6({a: 2, m() { return 3 }}));
+
+  var g1 = async (x = 1) => { return x };
+  assertEqualsAsync(1, () => g1());
+  assertEqualsAsync(1, () => g1(undefined));
+  assertEqualsAsync(2, () => g1(2));
+  assertEqualsAsync(null, () => g1(null));
+
+  var g2 = async (x, y = x) => { return x + y; };
+  assertEqualsAsync(8, () => g2(4));
+  assertEqualsAsync(8, () => g2(4, undefined));
+  assertEqualsAsync(6, () => g2(4, 2));
+
+  var g3 = async (x = 1, y) => { return x + y; };
+  assertEqualsAsync(8, () => g3(5, 3));
+  assertEqualsAsync(3, () => g3(undefined, 2));
+  assertEqualsAsync(6, () => g3(4, 2));
+
+  var g4 = async (x = () => 1) => { return x() };
+  assertEqualsAsync(1, () => g4());
+  assertEqualsAsync(1, () => g4(undefined));
+  assertEqualsAsync(2, () => g4(() => 2));
+  assertThrowsAsync(() => g4(null), TypeError);
+
+  var g5 = async (x, y = () => x) => { return x + y(); };
+  assertEqualsAsync(8, () => g5(4));
+  assertEqualsAsync(8, () => g5(4, undefined));
+  assertEqualsAsync(6, () => g5(4, () => 2));
+
+  var g6 = async (x = {a: 1, m() { return 2 }}) => { return x.a + x.m(); };
+  assertEqualsAsync(3, () => g6());
+  assertEqualsAsync(3, () => g6(undefined));
+  assertEqualsAsync(5, () => g6({a: 2, m() { return 3 }}));
+}());
+
+
+(function TestEvalInParameters() {
+  async function f1(x = eval(0)) { return x }
+  assertEqualsAsync(0, f1);
+  async function f2(x = () => eval(1)) { return x() }
+  assertEqualsAsync(1, f2);
+})();
+
+
+(function TestParameterScopingSloppy() {
+  var x = 1;
+
+  async function f1(a = x) { var x = 2; return a; }
+  assertEqualsAsync(1, f1);
+  async function f2(a = x) { function x() {}; return a; }
+  assertEqualsAsync(1, () => f2());
+  async function f3(a = eval("x")) { var x; return a; }
+  assertEqualsAsync(1, () => f3());
+  async function f31(a = eval("'use strict'; x")) { var x; return a; }
+  assertEqualsAsync(1, () => f31());
+  async function f4(a = function() { return x }) { var x; return a(); }
+  assertEqualsAsync(1, () => f4());
+  async function f5(a = () => x) { var x; return a(); }
+  assertEqualsAsync(1, () => f5());
+  async function f6(a = () => eval("x")) { var x; return a(); }
+  assertEqualsAsync(1, () => f6());
+  async function f61(a = () => { 'use strict'; return eval("x") }) { var x; return a(); }
+  assertEqualsAsync(1, () => f61());
+  async function f62(a = () => eval("'use strict'; x")) { var x; return a(); }
+  assertEqualsAsync(1, () => f62());
+
+  var g1 = async (a = x) => { var x = 2; return a; };
+  assertEqualsAsync(1, () => g1());
+  var g2 = async (a = x) => { function x() {}; return a; };
+  assertEqualsAsync(1, () => g2());
+  var g3 = async (a = eval("x")) => { var x; return a; };
+  assertEqualsAsync(1, g3);
+  var g31 = async (a = eval("'use strict'; x")) => { var x; return a; };
+  assertEqualsAsync(1, () => g31());
+  var g4 = async (a = function() { return x }) => { var x; return a(); };
+  assertEqualsAsync(1, () => g4());
+  var g5 = async (a = () => x) => { var x; return a(); };
+  assertEqualsAsync(1, () => g5());
+  var g6 = async (a = () => eval("x")) => { var x; return a(); };
+  assertEqualsAsync(1, () => g6());
+  var g61 = async (a = () => { 'use strict'; return eval("x") }) => { var x; return a(); };
+  assertEqualsAsync(1, () => g61());
+  var g62 = async (a = () => eval("'use strict'; x")) => { var x; return a(); };
+  assertEqualsAsync(1, () => g62());
+
+  var f11 = async function f(x = f) { var f; return x; }
+  assertEqualsAsync(f11, f11);
+  var f12 = async function f(x = f) { function f() {}; return x; }
+  assertEqualsAsync(f12, f12);
+  var f13 = async function f(f = 7, x = f) { return x; }
+  assertEqualsAsync(7, f13);
+
+  var o1 = {f: async function(x = this) { return x; }};
+  assertEqualsAsync(o1, () => o1.f());
+  assertEqualsAsync(1, () => o1.f(1));
+})();
+
+(function TestParameterScopingStrict() {
+  "use strict";
+  var x = 1;
+
+  async function f1(a = x) { let x = 2; return a; }
+  assertEqualsAsync(1, () => f1());
+  async function f2(a = x) { const x = 2; return a; }
+  assertEqualsAsync(1, () => f2());
+  async function f3(a = x) { function x() {}; return a; }
+  assertEqualsAsync(1, () => f3());
+  async function f4(a = eval("x")) { var x; return a; }
+  assertEqualsAsync(1, () => f4());
+  async function f5(a = () => eval("x")) { var x; return a(); }
+  assertEqualsAsync(1, () => f5());
+
+  var g1 = async (a = x) => { let x = 2; return a; };
+  assertEqualsAsync(1, () => g1());
+  var g2 = async (a = x) => { const x = 2; return a; };
+  assertEqualsAsync(1, () => g2());
+  var g3 = async (a = x) => { function x() {}; return a; };
+  assertEqualsAsync(1, () => g3());
+  var g4 = async (a = eval("x")) => { var x; return a; };
+  assertEqualsAsync(1, () => g4());
+  var g5 = async (a = () => eval("x")) => { var x; return a(); };
+  assertEqualsAsync(1, () => g5());
+
+  var f11 = async function f(x = f) { let f; return x; }
+  assertEqualsAsync(f11, f11);
+  var f12 = async function f(x = f) { const f = 0; return x; }
+  assertEqualsAsync(f12, f12);
+  var f13 = async function f(x = f) { function f() {}; return x; }
+  assertEqualsAsync(f13, f13);
+})();
+
+(function TestSloppyEvalScoping() {
+  var x = 1;
+
+  async function f1(y = eval("var x = 2")) { with ({}) { return x; } }
+  assertEqualsAsync(1, () => f1());
+  async function f2(y = eval("var x = 2"), z = x) { return z; }
+  assertEqualsAsync(1, () => f2());
+  assertEqualsAsync(1, () => f2(0));
+  async function f3(y = eval("var x = 2"), z = eval("x")) { return z; }
+  assertEqualsAsync(1, () => f3());
+  assertEqualsAsync(1, () => f3(0));
+  async function f8(y = (eval("var x = 2"), x)) { return y; }
+  assertEqualsAsync(2, () => f8());
+  assertEqualsAsync(0, () => f8(0));
+
+  async function f11(z = eval("var y = 2")) { return y; }
+  assertThrowsAsync(f11, ReferenceError);
+  async function f12(z = eval("var y = 2"), b = y) {}
+  assertThrowsAsync(f12, ReferenceError);
+  async function f13(z = eval("var y = 2"), b = eval("y")) {}
+  assertThrowsAsync(f13, ReferenceError);
+
+  async function f21(f = () => x) { eval("var x = 2"); return f() }
+  assertEqualsAsync(1, () => f21());
+  assertEqualsAsync(3, () => f21(() => 3));
+  async function f22(f = () => eval("x")) { eval("var x = 2"); return f() }
+  assertEqualsAsync(1, () => f22());
+  assertEqualsAsync(3, () => f22(() => 3));
+
+  var g1 = async (y = eval("var x = 2")) => { with ({}) { return x; } };
+  assertEqualsAsync(1, () => g1());
+  var g2 = async (y = eval("var x = 2"), z = x) => { return z; };
+  assertEqualsAsync(1, () => g2());
+  assertEqualsAsync(1, () => g2(0));
+  var g3 = async (y = eval("var x = 2"), z = eval("x")) => { return z; };
+  assertEqualsAsync(1, () => g3());
+  assertEqualsAsync(1, () => g3(0));
+  var g8 = async (y = (eval("var x = 2"), x)) => { return y; };
+  assertEqualsAsync(2, () => g8());
+  assertEqualsAsync(0, () => g8(0));
+
+  var g11 = async (z = eval("var y = 2")) => { return y; };
+  assertThrowsAsync(g11, ReferenceError);
+  var g12 = async (z = eval("var y = 2"), b = y) => {};
+  assertThrowsAsync(g12, ReferenceError);
+  var g13 = async (z = eval("var y = 2"), b = eval("y")) => {};
+  assertThrowsAsync(g13, ReferenceError);
+
+  var g21 = async (f = () => x) => { eval("var x = 2"); return f() };
+  assertEqualsAsync(1, () => g21());
+  assertEqualsAsync(3, () => g21(() => 3));
+  var g22 = async (f = () => eval("x")) => { eval("var x = 2"); return f() };
+  assertEqualsAsync(1, () => g22());
+  assertEqualsAsync(3, () => g22(() => 3));
+})();
+
+
+(function TestStrictEvalScoping() {
+  'use strict';
+  var x = 1;
+
+  async function f1(y = eval("var x = 2")) { return x; }
+  assertEqualsAsync(1, () => f1());
+  async function f2(y = eval("var x = 2"), z = x) { return z; }
+  assertEqualsAsync(1, () => f2());
+  assertEqualsAsync(1, () => f2(0));
+  async function f3(y = eval("var x = 2"), z = eval("x")) { return z; }
+  assertEqualsAsync(1, () => f3());
+  assertEqualsAsync(1, () => f3(0));
+  async function f8(y = (eval("var x = 2"), x)) { return y; }
+  assertEqualsAsync(1, () => f8());
+  assertEqualsAsync(0, () => f8(0));
+
+  async function f11(z = eval("var y = 2")) { return y; }
+  assertThrowsAsync(f11, ReferenceError);
+  async function f12(z = eval("var y = 2"), b = y) {}
+  assertThrowsAsync(f12, ReferenceError);
+  async function f13(z = eval("var y = 2"), b = eval("y")) {}
+  assertThrowsAsync(f13, ReferenceError);
+
+  async function f21(f = () => x) { eval("var x = 2"); return f() }
+  assertEqualsAsync(1, () => f21());
+  assertEqualsAsync(3, () => f21(() => 3));
+  async function f22(f = () => eval("x")) { eval("var x = 2"); return f() }
+  assertEqualsAsync(1, () => f22());
+  assertEqualsAsync(3, () => f22(() => 3));
+})();
+
+(function TestParameterTDZSloppy() {
+  async function f1(a = x, x) { return a }
+  assertThrowsAsync(() => f1(undefined, 4), ReferenceError);
+  assertEqualsAsync(4, () => f1(4, 5));
+  async function f2(a = eval("x"), x) { return a }
+  assertThrowsAsync(() => f2(undefined, 4), ReferenceError);
+  assertEqualsAsync(4, () => f2(4, 5));
+  async function f3(a = eval("'use strict'; x"), x) { return a }
+  assertThrowsAsync(() => f3(undefined, 4), ReferenceError);
+  assertEqualsAsync(4, () => f3(4, 5));
+  async function f4(a = () => x, x) { return a() }
+  assertEqualsAsync(4, () => f4(() => 4, 5));
+  async function f5(a = () => eval("x"), x) { return a() }
+  assertEqualsAsync(4, () => f5(() => 4, 5));
+  async function f6(a = () => eval("'use strict'; x"), x) { return a() }
+  assertEqualsAsync(4, () => f6(() => 4, 5));
+
+  async function f11(a = x, x = 2) { return a }
+  assertThrowsAsync(() => f11(), ReferenceError);
+  assertThrowsAsync(() => f11(undefined), ReferenceError);
+  assertThrowsAsync(() => f11(undefined, 4), ReferenceError);
+  assertEqualsAsync(4, () => f1(4, 5));
+  async function f12(a = eval("x"), x = 2) { return a }
+  assertThrowsAsync(() => f12(), ReferenceError);
+  assertThrowsAsync(() => f12(undefined), ReferenceError);
+  assertThrowsAsync(() => f12(undefined, 4), ReferenceError);
+  assertEqualsAsync(4, () => f12(4, 5));
+  async function f13(a = eval("'use strict'; x"), x = 2) { return a }
+  assertThrowsAsync(() => f13(), ReferenceError);
+  assertThrowsAsync(() => f13(undefined), ReferenceError);
+  assertThrowsAsync(() => f13(undefined, 4), ReferenceError);
+  assertEqualsAsync(4, () => f13(4, 5));
+
+  async function f21(x = function() { return a }, ...a) { return x()[0] }
+  assertEqualsAsync(4, () => f21(undefined, 4));
+  async function f22(x = () => a, ...a) { return x()[0] }
+  assertEqualsAsync(4, () => f22(undefined, 4));
+  async function f23(x = () => eval("a"), ...a) { return x()[0] }
+  assertEqualsAsync(4, () => f23(undefined, 4));
+  async function f24(x = () => {'use strict'; return eval("a") }, ...a) {
+    return x()[0]
+  }
+  assertEqualsAsync(4, () => f24(undefined, 4));
+  async function f25(x = () => eval("'use strict'; a"), ...a) { return x()[0] }
+  assertEqualsAsync(4, () => f25(undefined, 4));
+
+  var g1 = async (x = function() { return a }, ...a) => { return x()[0] };
+  assertEqualsAsync(4, () => g1(undefined, 4));
+  var g2 = async (x = () => a, ...a) => { return x()[0] };
+  assertEqualsAsync(4, () => g2(undefined, 4));
+})();
+
+(function TestParameterTDZStrict() {
+  "use strict";
+
+  async function f1(a = eval("x"), x) { return a }
+  assertThrowsAsync(() => f1(undefined, 4), ReferenceError);
+  assertEqualsAsync(4, () => f1(4, 5));
+  async function f2(a = () => eval("x"), x) { return a() }
+  assertEqualsAsync(4, () => f2(() => 4, 5));
+
+  async function f11(a = eval("x"), x = 2) { return a }
+  assertThrowsAsync(() => f11(), ReferenceError);
+  assertThrowsAsync(() => f11(undefined), ReferenceError);
+  assertThrowsAsync(() => f11(undefined, 4), ReferenceError);
+  assertEqualsAsync(4, () => f11(4, 5));
+
+  async function f21(x = () => eval("a"), ...a) { return x()[0] }
+  assertEqualsAsync(4, () => f21(undefined, 4));
+})();
+
+(function TestArgumentsForNonSimpleParameters() {
+  async function f1(x = 900) { arguments[0] = 1; return x }
+  assertEqualsAsync(9, () => f1(9));
+  assertEqualsAsync(900, () => f1());
+  async function f2(x = 1001) { x = 2; return arguments[0] }
+  assertEqualsAsync(10, () => f2(10));
+  assertEqualsAsync(undefined, () => f2());
+}());
+
+
+(function TestFunctionLength() {
+   assertEquals(0, (async function(x = 1) {}).length);
+   assertEquals(0, (async function(x = 1, ...a) {}).length);
+   assertEquals(1, (async function(x, y = 1) {}).length);
+   assertEquals(1, (async function(x, y = 1, ...a) {}).length);
+   assertEquals(2, (async function(x, y, z = 1) {}).length);
+   assertEquals(2, (async function(x, y, z = 1, ...a) {}).length);
+   assertEquals(1, (async function(x, y = 1, z) {}).length);
+   assertEquals(1, (async function(x, y = 1, z, ...a) {}).length);
+   assertEquals(1, (async function(x, y = 1, z, v = 2) {}).length);
+   assertEquals(1, (async function(x, y = 1, z, v = 2, ...a) {}).length);
+})();
+
+(function TestDirectiveThrows() {
+  "use strict";
+
+  assertThrows("(async function(x=1){'use strict';})", SyntaxError);
+  assertThrows("(async function(a, x=1){'use strict';})", SyntaxError);
+  assertThrows("(async function({x}){'use strict';})", SyntaxError);
+})();