Implement ES6 @@isConcatSpreadable

test/mjsunit/harmony/array-concat.js

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+// Copyright 2014 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.
 
-/**
- * @fileoverview Test concat on small and large arrays
- */
+// Flags: --harmony-arrays --harmony-classes
+
+"use strict";
+
+(function testArrayConcatArity() {

[Dmitry Lomov (no reviews), 2014/12/10 14:41:59]

Please add a test that sets isConcatSpreadable on a typed array (small and
large)

[caitp (gmail), 2014/12/10 15:29:20]

Acknowledged --- but reading the draft, I am not seeing
TypedArrays/ArrayBuffers/DataViews as concat-spreadable, unless I'm missing
something. So I think these tests are just asserting that the typed arrays are
NOT spread, is that right?

+  assertEquals(1, Array.prototype.concat.length);
+})();
+
+
+(function testArrayConcatNoPrototype() {
+  assertEquals(void 0, Array.prototype.concat.prototype);
+})();
+
+
+(function testArrayConcatDescriptor() {
+  var desc = Object.getOwnPropertyDescriptor(Array.prototype, 'concat');
+  assertEquals(false, desc.enumerable);
+})();
+
+
+(function testConcatArrayLike() {
+  var obj = {
+    "length": 6,
+    "1": "A",
+    "3": "B",
+    "5": "C"
+  };
+  obj[Symbol.isConcatSpreadable] = true;
+  var obj2 = { length: 3, "0": "0", "1": "1", "2": "2" };
+  var arr = ["X", "Y", "Z"];
+  assertEquals([void 0, "A", void 0, "B", void 0, "C",
+               { "length": 3, "0": "0", "1": "1", "2": "2" },
+               "X", "Y", "Z"], Array.prototype.concat.call(obj, obj2, arr));
+})();
+
+
+(function testConcatHoleyArray() {
+  var arr = [];
+  arr[4] = "Item 4";
+  arr[8] = "Item 8";
+  var arr2 = [".", "!", "?"];
+  assertEquals([void 0, void 0, void 0, void 0, "Item 4", void 0, void 0,
+                void 0, "Item 8", ".", "!", "?"], arr.concat(arr2));
+})();
+
+
+(function testIsConcatSpreadableGetterThrows() {
+  function MyError() {}
+  var obj = {};
+  Object.defineProperty(obj, Symbol.isConcatSpreadable, {
+    get: function() { throw new MyError(); }
+  });
+
+  assertThrows(function() {
+    [].concat(obj);
+  }, MyError);
+
+  assertThrows(function() {
+    Array.prototype.concat.call(obj, 1, 2, 3);
+  }, MyError);
+})();
+
+
+(function testConcatLengthThrows() {
+  function MyError() {}
+  var obj = {};
+  obj[Symbol.isConcatSpreadable] = true;
+  Object.defineProperty(obj, "length", {
+    get: function() { throw new MyError(); }
+  });
+
+  assertThrows(function() {
+    [].concat(obj);
+  }, MyError);
+
+  assertThrows(function() {
+    Array.prototype.concat.call(obj, 1, 2, 3);
+  }, MyError);
+})();
+
+
+(function testConcatArraySubclass() {
+  // TODO(caitp): when concat is called on instances of classes which extend
+  // Array, they should:
+  //
+  // - return an instance of the class, rather than an Array instance (if from
+  //   same Realm)
+  // - always treat such classes as concat-spreadable
+})();
+
+
+(function testConcatNonArray() {
+  class NonArray {
+    constructor() { Array.apply(this, arguments); }
+  };
+
+  var obj = new NonArray(1,2,3);
+  var result = Array.prototype.concat.call(obj, 4, 5, 6);
+  assertEquals(Array, result.constructor);
+  assertEquals([obj,4,5,6], result);
+  assertFalse(result instanceof NonArray);
+})();
+
+
+// ES5 tests
 
 var poses;
+var pos;
 
 poses = [140, 4000000000];
 while (pos = poses.shift()) {
   var a = new Array(pos);
   var array_proto = [];
   a.__proto__ = array_proto;
   assertEquals(pos, a.length);
   a.push('foo');
   assertEquals(pos + 1, a.length);
   var b = ['bar'];
@@ skipping 185 matching lines @@
 function mkGetter(i) { return function() { trace.push(i); }; }
 arr3.length = 10000;
 for (var i = 0; i < 100; i++) {
   Object.defineProperty(arr3, i * i, {get: mkGetter(i)});
   expectedTrace[i] = i;
   expectedTrace[100 + i] = i;
 }
 var r4 = [0].concat(arr3, arr3);
 assertEquals(1 + arr3.length * 2, r4.length);
 assertEquals(expectedTrace, trace);