Change SmartMove no-op behavior to match SimpleMove (and ES6 spec)

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
index 0eb299a0cee2a145396c2e7036d2237667c256c7..50aab4f52a4b58a316053604c719d4465c48be9a 100644
--- a/test/mjsunit/array-unshift.js
+++ b/test/mjsunit/array-unshift.js
@@ -37,9 +37,7 @@
 })();
 
 
-// Check that unshift with no args has a side-effect of
-// filling the holes with elements from the prototype
-// (if present, of course)
+// Check that unshift with no args has no side-effects.
 (function() {
   var len = 3;
   var array = new Array(len);
@@ -65,15 +63,15 @@
   assertTrue(delete Array.prototype[0]);
   assertTrue(delete Array.prototype[2]);
 
-  // unshift makes array own 0 and 2...
-  assertTrue(array.hasOwnProperty(0));
+  // array still owns nothing...
+  assertFalse(array.hasOwnProperty(0));

[Michael Starzinger, 2014/10/22 08:45:50]

I am not convinced that this is actually spec-compliant behavior. The spec says
Array.prototype.unshift should always run through a moving loop, no matter how
many arguments are passed. The loop performs [[HasProperty]], [[Get]] and
[[Put]] on all present elements. The effect of that should be that "non-own data
properties" turn into "own data properties" just like this test originally
expected.

[adamk, 2014/10/22 17:15:35]

This appears to be a difference between ES5 and ES6, I should have checked both!
Here's ES6:

https://people.mozilla.org/~jorendorff/es6-draft.html#sec-array.prototype.uns...

In particular, step 7 is "If argCount > 0, then [run the loop]"

whereas, as you point out, ES5
(http://www.ecma-international.org/ecma-262/5.1/#sec-15.4.4.13) says nothing
about checking argCount.

Seems like something to ask an ES expert on, will start by adding rossberg and
arv to this review.

   assertFalse(array.hasOwnProperty(1));
-  assertTrue(array.hasOwnProperty(2));
+  assertFalse(array.hasOwnProperty(2));
 
   // ... so they are not affected be delete.
-  assertEquals(array[0], at0);
+  assertEquals(array[0], undefined);
   assertEquals(array[1], undefined);
-  assertEquals(array[2], at2);
+  assertEquals(array[2], undefined);
 })();
 
 
@@ -115,9 +113,7 @@
   assertTrue(delete Array.prototype[7]);
 })();
 
-// Check that unshift with no args has a side-effect of
-// filling the holes with elements from the prototype
-// (if present, of course)
+// Check that unshift with no args has no side-effects.
 (function() {
   var len = 3;
   var array = new Array(len);
@@ -142,12 +138,12 @@
 
   assertEquals(len, array.unshift());
 
-  // unshift makes array own 0 and 2...
-  assertTrue(array.hasOwnProperty(0));
+  // array still owns nothing.
+  assertFalse(array.hasOwnProperty(0));
   assertFalse(array.hasOwnProperty(1));
-  assertTrue(array.hasOwnProperty(2));
+  assertFalse(array.hasOwnProperty(2));
 
-  // ... so they are not affected be delete.
+  // ... but still sees values from array_proto.
   assertEquals(array[0], at0);
   assertEquals(array[1], undefined);
   assertEquals(array[2], at2);