Introduce builtin for Array.unshift function.

test/mjsunit/array-unshift.js

Index: test/mjsunit/array-unshift.js
diff --git a/test/mjsunit/array-unshift.js b/test/mjsunit/array-unshift.js
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+++ b/test/mjsunit/array-unshift.js
@@ -0,0 +1,116 @@
+// Copyright 2010 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Check that unshifting array of holes keeps the original array
+// as array of holes
+(function() {
+  var array = new Array(10);
+  assertEquals(13, array.unshift('1st', '2ns', '3rd'));
+  assertTrue(0 in array);
+  assertTrue(1 in array);
+  assertTrue(2 in array);
+  assertFalse(3 in array);
+})();
+
+
+// Check that unshif with no args has a side-effect of
+// feeling the holes with elements from the prototype
+// (if present, of course)
+(function() {
+  var len = 3;
+  var array = new Array(len);
+
+  var at0 = '@0';
+  var at2 = '@2';
+
+  Array.prototype[0] = at0;
+  Array.prototype[2] = at2;
+
+  // array owns nothing...
+  assertFalse(array.hasOwnProperty(0));
+  assertFalse(array.hasOwnProperty(1));
+  assertFalse(array.hasOwnProperty(2));
+
+  // ... but sees values from Array.prototype
+  assertEquals(array[0], at0);
+  assertEquals(array[1], undefined);
+  assertEquals(array[2], at2);
+
+  assertEquals(len, array.unshift());
+
+  assertTrue(delete Array.prototype[0]);
+  assertTrue(delete Array.prototype[2]);
+
+  // unshift makes array own 0 and 2...
+  assertTrue(array.hasOwnProperty(0));
+  assertFalse(array.hasOwnProperty(1));
+  assertTrue(array.hasOwnProperty(2));
+
+  // ... so they are not affected be delete.
+  assertEquals(array[0], at0);
+  assertEquals(array[1], undefined);
+  assertEquals(array[2], at2);
+})();
+
+
+// Now check the case with array of holes and some elements on prototype.
+(function() {
+  var len = 9;
+  var array = new Array(len);
+  Array.prototype[3] = "@3";
+  Array.prototype[7] = "@7";
+
+  assertEquals(len, array.length);
+  for (var i = 0; i < array.length; i++) {
+    assertEquals(array[i], Array.prototype[i]);
+  }
+
+  assertEquals(len + 1, array.unshift('head'));
+
+  assertEquals(len + 1, array.length);
+  // Note that unshift copies values from prototype into the array.
+  assertEquals(array[4], Array.prototype[3]);
+  assertTrue(array.hasOwnProperty(4));
+
+  assertEquals(array[8], Array.prototype[7]);
+  assertTrue(array.hasOwnProperty(8));
+
+  // ... but keeps the rest as holes:
+  Array.prototype[5] = "@5";
+  assertEquals(array[5], Array.prototype[5]);
+  assertFalse(array.hasOwnProperty(5));
+
+  assertEquals(array[3], Array.prototype[3]);
+  assertFalse(array.hasOwnProperty(3));
+
+  assertEquals(array[7], Array.prototype[7]);
+  assertFalse(array.hasOwnProperty(7));
+
+  assertTrue(delete Array.prototype[3]);
+  assertTrue(delete Array.prototype[5]);
+  assertTrue(delete Array.prototype[7]);
+})();