Add Array support for @@species and subclassing

test/mjsunit/harmony/array-species.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-species
+
+// Test the ES2015 @@species feature

[adamk, 2016/01/06 00:10:12]

More tests I'd like to see:

- Test that the length is passed to the constructor
- As noted elsewhere, that we erroneously fetch @@species twice

[Dan Ehrenberg, 2016/01/07 00:42:58]

Added those tests at the end

+
+'use strict';
+
+// Subclasses of Array construct themselves under map, etc
+
+class MyArray extends Array { }
+
+assertEquals(MyArray, new MyArray().map(()=>{}).constructor);
+assertEquals(MyArray, new MyArray().filter(()=>{}).constructor);
+assertEquals(MyArray, new MyArray().concat().constructor);
+assertEquals(MyArray, new MyArray().slice().constructor);
+assertEquals(MyArray, new MyArray().splice().constructor);
+
+// Subclasses can override @@species to return the another class
+
+class MyOtherArray extends Array {
+  static get [Symbol.species]() { return MyArray; }
+}
+
+assertEquals(MyArray, new MyOtherArray().map(()=>{}).constructor);
+assertEquals(MyArray, new MyOtherArray().filter(()=>{}).constructor);
+assertEquals(MyArray, new MyOtherArray().concat().constructor);
+assertEquals(MyArray, new MyOtherArray().slice().constructor);
+assertEquals(MyArray, new MyOtherArray().splice().constructor);
+
+// Array  methods on non-arrays return arrays
+
+class MyNonArray extends Array {
+  static get [Symbol.species]() { return MyObject; }
+}
+
+class MyObject { }
+
+assertEquals(MyObject, Array.prototype.map.call(new MyNonArray(), ()=>{}).constructor);

[adamk, 2016/01/06 00:10:12]

Please wrap at 80 chars here and below (dunno why we don't have a lint check for
js).

[Dan Ehrenberg, 2016/01/07 00:42:58]

Fixed

+assertEquals(MyObject, Array.prototype.filter.call(new MyNonArray(), ()=>{}).constructor);
+assertEquals(MyObject, Array.prototype.concat.call(new MyNonArray()).constructor);
+assertEquals(MyObject, Array.prototype.slice.call(new MyNonArray()).constructor);
+assertEquals(MyObject, Array.prototype.splice.call(new MyNonArray()).constructor);
+
+assertEquals(undefined, Array.prototype.map.call(new MyNonArray(), ()=>{}).length);
+assertEquals(undefined, Array.prototype.filter.call(new MyNonArray(), ()=>{}).length);
+assertEquals(undefined, Array.prototype.concat.call(new MyNonArray()).length);
+// slice and splice actually do explicitly define the length for some reason
+assertEquals(0, Array.prototype.slice.call(new MyNonArray()).length);
+assertEquals(0, Array.prototype.splice.call(new MyNonArray()).length);
+
+// Cross-realm Arrays build same-realm arrays
+
+var realm = Realm.create();
+assertEquals(Array, Array.prototype.map.call(Realm.eval(realm, "[]"), ()=>{}).constructor);
+assertFalse(Array === Realm.eval(realm, "[]").map(()=>{}).constructor);
+assertFalse(Array === Realm.eval(realm, "[].map(()=>{}).constructor"));
+
+// Defaults when constructor or @@species is missing or non-constructor
+
+class MyDefaultArray extends Array {
+  static get [Symbol.species]() { return undefined; }
+}
+assertEquals(Array, new MyDefaultArray().map(()=>{}).constructor);
+
+class MyOtherDefaultArray extends Array { }
+assertEquals(MyOtherDefaultArray, new MyOtherDefaultArray().map(()=>{}).constructor);
+MyOtherDefaultArray.prototype.constructor = undefined;
+assertEquals(Array, new MyOtherDefaultArray().map(()=>{}).constructor);
+
+// Exceptions propagated when getting constructor @@species throws
+
+class SpeciesError extends Error { }
+class ConstructorError extends Error { }
+class MyThrowingArray extends Array {
+  static get [Symbol.species]() { throw new SpeciesError; }
+}
+assertThrows(() => new MyThrowingArray().map(()=>{}), SpeciesError);
+Object.defineProperty(MyThrowingArray.prototype, 'constructor', {
+    get() { throw new ConstructorError; }
+});
+assertThrows(() => new MyThrowingArray().map(()=>{}), ConstructorError);
+
+// Previously unexpected errors from setting properties in arrays throw
+
+class FrozenArray extends Array {
+  constructor(...args) {
+    super(...args);
+    Object.freeze(this);
+  }
+}
+assertThrows(() => new FrozenArray([1]).map(()=>0), TypeError);
+assertThrows(() => new FrozenArray([1]).filter(()=>true), TypeError);
+assertThrows(() => new FrozenArray([1]).slice(0, 1), TypeError);
+assertThrows(() => new FrozenArray([1]).splice(0, 1), TypeError);
+assertThrows(() => new FrozenArray([1]).concat(), TypeError);