refactor($parse): change 'this' to a $parse keyword instead of scope field

BREAKING CHANGE:
- $scope['this'] no longer exits on the $scope object
- $parse-ed expressions no longer allow chaining 'this' such as this['this'] or $parent['this']
- 'this' in $parse-ed expressions can no longer be overriden, if a variable named 'this' is put on the scope it must be accessed using this['this']

Closes #9105

Author: jbedard

src/ng/parse.js

@@ -92,6 +92,11 @@ forEach({
   CONSTANTS[name] = constantGetter;
 });
 
+//Not quite a constant, but can be lex/parsed the same
+CONSTANTS['this'] = function(self) { return self; };
+CONSTANTS['this'].sharedGetter = true;
+
+
 //Operators - will be wrapped by binaryFn/unaryFn/assignment/filter
 var OPERATORS = extend(createMap(), {
     /* jshint bitwise : false */

src/ng/rootScope.js

@@ -128,7 +128,7 @@ function $RootScopeProvider(){
       this.$$phase = this.$parent = this.$$watchers =
                      this.$$nextSibling = this.$$prevSibling =
                      this.$$childHead = this.$$childTail = null;
-      this['this'] = this.$root =  this;
+      this.$root = this;
       this.$$destroyed = false;
       this.$$asyncQueue = [];
       this.$$postDigestQueue = [];
@@ -220,7 +220,6 @@ function $RootScopeProvider(){
           }
           child = new this.$$ChildScope();
         }
-        child['this'] = child;
         child.$parent = parent;
         child.$$prevSibling = parent.$$childTail;
         if (parent.$$childHead) {

test/ng/rootScopeSpec.js

@@ -51,8 +51,25 @@ describe('Scope', function() {
 
 
   describe('this', function() {
-    it('should have a \'this\'', inject(function($rootScope) {
-      expect($rootScope['this']).toEqual($rootScope);
+    it('should evaluate \'this\' to be the scope', inject(function($rootScope) {
+      var child = $rootScope.$new();
+      expect($rootScope.$eval('this')).toEqual($rootScope);
+      expect(child.$eval('this')).toEqual(child);
+    }));
+
+    it('\'this\' should not be recursive', inject(function($rootScope) {
+      expect($rootScope.$eval('this.this')).toBeUndefined();
+      expect($rootScope.$eval('$parent.this')).toBeUndefined();
+    }));
+
+    it('should not be able to overwrite the \'this\' keyword', inject(function($rootScope) {
+      $rootScope['this'] = 123;
+      expect($rootScope.$eval('this')).toEqual($rootScope);
+    }));
+
+    it('should be able to access a variable named \'this\'', inject(function($rootScope) {
+      $rootScope['this'] = 42;
+      expect($rootScope.$eval('this[\'this\']')).toBe(42);
     }));
   });