fix(angular): do not copy $$hashKey in copy/extend functions.

Copying the $$hashKey as part of copy/extend operations makes little
sense since hashkey is used primarily as an object id, especially in
the context of the ngRepeat directive. This change maintains the
existing $$hashKey of an object that is being copied into (likewise for
extend).
It is not uncommon to take an item in a collection, copy it,
and then append it to the collection. By copying the $$hashKey, this
leads to duplicate object errors with the current ngRepeat.

Closes #1875

src/Angular.js

@@ -195,6 +195,21 @@ function nextUid() {
   return uid.join('');
 }
 
+
+/**
+ * Set or clear the hashkey for an object.
+ * @param obj object 
+ * @param h the hashkey (!truthy to delete the hashkey)
+ */
+function setHashKey(obj, h) {
+  if (h) {
+    obj.$$hashKey = h;
+  }
+  else {
+    delete obj.$$hashKey;
+  }
+}
+
 /**
  * @ngdoc function
  * @name angular.extend
@@ -208,6 +223,7 @@ function nextUid() {
  * @param {...Object} src Source object(s).
  */
 function extend(dst) {
+  var h = dst.$$hashKey;
   forEach(arguments, function(obj){
     if (obj !== dst) {
       forEach(obj, function(value, key){
@@ -215,6 +231,8 @@ function extend(dst) {
       });
     }
   });
+
+  setHashKey(dst,h);
   return dst;
 }
 
@@ -569,12 +587,14 @@ function copy(source, destination){
         destination.push(copy(source[i]));
       }
     } else {
+      var h = destination.$$hashKey;
       forEach(destination, function(value, key){
         delete destination[key];
       });
       for ( var key in source) {
         destination[key] = copy(source[key]);
       }
+      setHashKey(destination,h);
     }
   }
   return destination;

test/AngularSpec.js

@@ -98,6 +98,63 @@ describe('angular', function() {
       src = dst = [2, 4];
       expect(function() { copy(src, dst); }).toThrow("Can't copy equivalent objects or arrays");
     });
+
+    it('should not copy the private $$hashKey', function() {
+      var src,dst;
+      src = {};
+      hashKey(src);
+      dst = copy(src);
+      expect(hashKey(dst)).not.toEqual(hashKey(src));
+    });
+
+    it('should retain the previous $$hashKey', function() {
+      var src,dst,h;
+      src = {};
+      dst = {};
+      // force creation of a hashkey
+      h = hashKey(dst);
+      hashKey(src);
+      dst = copy(src,dst);
+
+      // make sure we don't copy the key
+      expect(hashKey(dst)).not.toEqual(hashKey(src));
+      // make sure we retain the old key
+      expect(hashKey(dst)).toEqual(h);
+    });
+  });
+
+  describe("extend", function() {
+
+    it('should not copy the private $$hashKey', function() {
+      var src,dst;
+      src = {};
+      dst = {};
+      hashKey(src);
+      dst = extend(dst,src);
+      expect(hashKey(dst)).not.toEqual(hashKey(src));
+    });
+
+    it('should retain the previous $$hashKey', function() {
+      var src,dst,h;
+      src = {};
+      dst = {};
+      h = hashKey(dst);
+      hashKey(src);
+      dst = extend(dst,src);
+      // make sure we don't copy the key
+      expect(hashKey(dst)).not.toEqual(hashKey(src));
+      // make sure we retain the old key
+      expect(hashKey(dst)).toEqual(h);
+    });
+
+    it('should work when extending with itself', function() {
+      var src,dst,h;
+      dst = src = {};
+      h = hashKey(dst);
+      dst = extend(dst,src);
+      // make sure we retain the old key
+      expect(hashKey(dst)).toEqual(h);
+    });
   });
 
   describe('shallow copy', function() {