Implement Symbol.isConcatSpreadable (#3307)

Algorithm is based on ECMA-262 v6, 22.1.3.1.1

JerryScript-DCO-1.0-Signed-off-by: Adam Szilagyi aszilagy@inf.u-szeged.hu

tests/jerry/es2015/symbol-isconcatspreadable.js

@@ -0,0 +1,81 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Test with regular arrays
+var alpha = ['a', 'b', 'c'];
+var numeric = [1, 2, 3];
+
+var alphaNumeric = alpha.concat(numeric);
+assert(JSON.stringify(alphaNumeric) === '["a","b","c",1,2,3]');
+assert(alphaNumeric.length === 6);
+
+numeric[Symbol.isConcatSpreadable] = false;
+alphaNumeric = alpha.concat(numeric);
+assert(JSON.stringify(alphaNumeric) === '["a","b","c",[1,2,3]]');
+assert(alphaNumeric.length === 4);
+
+numeric[Symbol.isConcatSpreadable] = true;
+
+// Test with array-like object
+var fakeArray = {
+  [Symbol.isConcatSpreadable]: true,
+  length: 2,
+  0: 4,
+  1: 5
+}
+
+var numericArray = numeric.concat(fakeArray);
+assert(JSON.stringify(numericArray) === '[1,2,3,4,5]');
+assert(numericArray.length === 5);
+
+fakeArray[Symbol.isConcatSpreadable] = false;
+numericArray = numeric.concat(fakeArray);
+assert(JSON.stringify(numericArray) === '[1,2,3,{"0":4,"1":5,"length":2}]');
+assert(numericArray.length === 4);
+
+// Test with object
+var obj = { 0: 'd' };
+
+var alphaObj = alpha.concat(obj);
+assert(JSON.stringify(alphaObj) === '["a","b","c",{"0":"d"}]');
+assert(alphaObj.length === 4);
+
+obj[Symbol.isConcatSpreadable] = true;
+alphaObj = alpha.concat(obj);
+assert(JSON.stringify(alphaObj) === '["a","b","c"]');
+assert(alphaObj.length === 3);
+
+// Test with boolean
+var bool = true;
+var numericBool = numeric.concat(bool);
+assert(JSON.stringify(numericBool) === '[1,2,3,true]');
+assert(numericBool.length === 4);
+
+bool[Symbol.isConcatSpreadable] = false;
+numericBool = numeric.concat(bool);
+assert(JSON.stringify(numericBool) === '[1,2,3,true]');
+assert(numericBool.length === 4);
+
+// Test when unable to concat
+var array1 = [];
+var array2 = [];
+Object.defineProperty(array2, '0', { 'get' : function () {throw new ReferenceError ("foo"); } });
+
+try {
+  array1.concat(array2);
+  assert(false);
+} catch (e) {
+  assert(e.message === "foo");
+  assert(e instanceof ReferenceError);
+}