fix($parse): correctly assign expressions who's path is undefined and that use brackets notation

Closes #8039

src/ng/parse.js

@@ -696,7 +696,9 @@ Parser.prototype = {
       return getter(self || object(scope, locals));
     }, {
       assign: function(scope, value, locals) {
-        return setter(object(scope, locals), field, value, parser.text, parser.options);
+        var o = object(scope, locals);
+        if (!o) object.assign(scope, o = {});
+        return setter(o, field, value, parser.text, parser.options);
       }
     });
   },
@@ -726,10 +728,11 @@ Parser.prototype = {
       return v;
     }, {
       assign: function(self, value, locals) {
-        var key = indexFn(self, locals);
+        var key = ensureSafeMemberName(indexFn(self, locals), parser.text);
         // prevent overwriting of Function.constructor which would break ensureSafeObject check
-        var safe = ensureSafeObject(obj(self, locals), parser.text);
-        return safe[key] = value;
+        var o = ensureSafeObject(obj(self, locals), parser.text);
+        if (!o) obj.assign(self, o = {});
+        return o[key] = value;
       }
     });
   },

test/ng/parseSpec.js

@@ -1089,6 +1089,22 @@ describe('parser', function() {
             fn.assign(scope, 123);
             expect(scope).toEqual({a:123});
           }));
+
+          it('should expose working assignment function for expressions ending with brackets', inject(function($parse) {
+            var fn = $parse('a.b["c"]');
+            expect(fn.assign).toBeTruthy();
+            var scope = {};
+            fn.assign(scope, 123);
+            expect(scope.a.b.c).toEqual(123);
+          }));
+
+          it('should expose working assignment function for expressions with brackets in the middle', inject(function($parse) {
+            var fn = $parse('a["b"].c');
+            expect(fn.assign).toBeTruthy();
+            var scope = {};
+            fn.assign(scope, 123);
+            expect(scope.a.b.c).toEqual(123);
+          }));
         });