[es6] implement default parameters via desugaring

test/mjsunit/harmony/default-parameters.js

+// Copyright 2015 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-default-parameters --harmony-arrow-functions
+
+function return_specified() { return "specified"; }
+
+var method_returns_specified = {
+  method() { return "specified"; }
+};
+
+
+(function testDefaultFunctions() {
+  function optional_function(handler = function() { }) {
+    assertEquals("function", typeof handler);
+
+    // TODO(caitp): infer function name correctly
+    // (https://code.google.com/p/v8/issues/detail?id=3699)
+    // assertEquals("handler", handler.name);
+
+    return handler();
+  }
+  assertEquals(undefined, optional_function());
+  assertEquals(undefined, optional_function(undefined));
+  assertEquals("specified", optional_function(return_specified));
+})();
+
+
+(function testDefaultFunctionReferencesParameters() {
+  function fn1(handler = function() { return value; }, value) {
+    return handler();
+  }
+  assertEquals(undefined, fn1());
+  assertEquals(undefined, fn1(undefined, undefined));
+  assertEquals(1, fn1(undefined, 1));
+
+  function fn2(value, handler = function() { return value; }) {
+    return handler();
+  }
+  assertEquals(undefined, fn2());
+  assertEquals(undefined, fn2(undefined));
+  assertEquals(1, fn2(1));
+})();
+
+
+(function testDefaultObjects() {
+  function optional_object(object = { method() { return "method"; } }) {
+    assertEquals("object", typeof object);
+
+    assertEquals("function", typeof object.method);
+    return object.method();
+  }
+
+  assertEquals("method", optional_object());
+  assertEquals("method", optional_object(undefined));
+  assertEquals("specified", optional_object(method_returns_specified));
+
+
+  assertEquals(4, (function(x = { a: 4 }) { return x.a; })());
+  assertEquals(5, (function(x, y = { a: x }) { return y.a; })(5));
+  // TODO(caitp): this is broken :(
+  // assertEquals(6, (function(x, y = { a: eval("x") }) { return y.a; })(6));
+})();
+
+
+// TDZ
+
+(function testReferencesUninitializedParameter() {
+  assertThrows(function(a = b, b) {}, ReferenceError);
+})();
+
+
+(function testEvalReferencesUninitializedParameter() {
+  assertThrows( function(x = { a: y }, y) { return x.a; }, ReferenceError);
+
+  // TODO(caitp): these shouldn't fail
+  // assertThrows(function(a = eval("b"), b = 0) { return a; }, ReferenceError);
+  // assertThrows(
+  //    function(x = { a: eval("y") }, y) { return x.a; }, ReferenceError);
+})();
+
+
+(function testReferencesInitializedParameter() {
+  assertEquals(1, (function(a = 1, b = a) { return b; })());
+})();
+
+
+// Scoping
+//
+// TODO(caitp): fix scoping --- var declarations in function body can't be
+// resolved in formal parameters
+// assertThrows(function referencesVariableBodyDeclaration(a = body_var) {
+//   var body_var = true;
+//   return a;
+// }, ReferenceError);
+
+
+// TODO(caitp): default function length does not include any parameters
+// following the first optional parameter
+// assertEquals(0, (function(a = 1) {}).length);
+// assertEquals(1, (function(a, b = 1) {}).length);
+// assertEquals(2, (function(a, b, c = 1) {}).length);
+// assertEquals(3, (function(a, b, c, d = 1) {}).length);
+// assertEquals(1, (function(a, b = 1, c, d = 1) {}).length);
+
+
+(function testInitializerReferencesThis() {
+  var O = {};
+  function fn(x = this) { return x; }
+  assertEquals(O, fn.call(O));
+
+  function fn2(x = () => this) { return x(); }
+  assertEquals(O, fn2.call(O));
+})();
+
+
+(function testInitializerReferencesSelf() {
+  function fn(x, y = fn) { return x ? y(false) + 1 : 0 }
+  assertEquals(1, fn(true));
+})();
+
+
+(function testInitializerEvalParameter() {
+  // TODO(caitp): should not fail
+  // assertEquals(7, (function(x, y = eval("x")) { return y; })(7));
+  // assertEquals(9, (function(x = () => eval("y"), y = 9) { return x(); })());
+})();