fix(ngRepeat): support complex assignable aliasAs expressions

Parse aliasAs as an expression, and assert that the expression is assignable.

BREAKING CHANGE

Previously, any name passed as an expression would make up a single property name, including constant
values such as 1, NaN, null, undefined, or even expressions such as function calls or boolean expressions.

Now, more complex expressions are possible, allowing the collection alias to be assigned as a property
of an object --- however, if the expression is not determined to be assignable, it will throw.

Fixes angular#8438

Author: caitp

docs/content/error/ngRepeat/nonassign.ngdoc

@@ -0,0 +1,10 @@
+@ngdoc error
+@name ngRepeat:nonassign
+@fullName Non-assignable Expression
+@description
+
+Occurs when there is a syntax error in an {@link ng.directive:ngRepeat ngRepeat} expression which is expected to be assignable.=
+
+The {@link ng.directive:ngRepeat ngRepeat} directive's `alias as` syntax is used to assign an alias for the processed collection in scope.
+
+If the expression is not assignable (such as a literal value or a function call or comparison operation), the expression is unassignable.

src/ng/directive/ngRepeat.js

@@ -232,9 +232,13 @@ var ngRepeatDirective = ['$parse', '$animate', function($parse, $animate) {
 
         lhs = match[1];
         rhs = match[2];
-        aliasAs = match[3];
+        aliasAs = match[3] && $parse(match[3]);
         trackByExp = match[4];
 
+        if (aliasAs && !aliasAs.assign) {
+          throw ngRepeatMinErr('nonassign', "Expected collection alias to be an assignable expression but got '{0}'.", match[3]);
+        }
+
         if (trackByExp) {
           trackByExpGetter = $parse(trackByExp);
           trackByIdExpFn = function(key, value, index) {
@@ -286,7 +290,7 @@ var ngRepeatDirective = ['$parse', '$animate', function($parse, $animate) {
               elementsToRemove;
 
           if (aliasAs) {
-            $scope[aliasAs] = collection;
+            aliasAs.assign($scope, collection);
           }
 
           var updateScope = function(scope, index) {

test/ng/directive/ngRepeatSpec.js

@@ -424,6 +424,71 @@ describe('ngRepeat', function() {
 
       expect(trim(element.text())).toEqual('No results found...');
     });
+
+
+    it('should support complex assignable expressions', function() {
+      element = $compile(
+        '<div>' +
+        '  <div ng-repeat="item in items | filter:x as ngRepeat.results track by $index">{{item}}</div>' +
+        '</div>')(scope);
+
+      scope.x = 'bl';
+      scope.items = [
+        { name : 'red' },
+        { name : 'blue' },
+        { name : 'green' },
+        { name : 'black' },
+        { name : 'orange' },
+        { name : 'blonde' }
+      ];
+      scope.$digest();
+      expect(scope.ngRepeat).toEqual({
+        results: [
+          { name : 'blue' },
+          { name : 'black' },
+          { name : 'blonde' }
+        ]
+      });
+    });
+
+
+    it('should throw if expression is not assignable', inject(function($exceptionHandler) {
+      element = $compile(
+        '<div>' +
+        '  <div ng-repeat="item in items | filter:x as null track by $index">{{item}}</div>' +
+        '</div>')(scope);
+
+      scope.x = 'bl';
+      scope.items = [
+        { name : 'red' },
+        { name : 'blue' },
+        { name : 'green' },
+        { name : 'black' },
+        { name : 'orange' },
+        { name : 'blonde' }
+      ];
+
+      expect($exceptionHandler.errors.shift()[0].message).
+        toMatch(/^\[ngRepeat:nonassign\] Expected collection alias to be an assignable expression but got \'null\'\./);
+    }));
+
+
+    it('should throw if alias as expression is an assignment expression', inject(function($exceptionHandler) {
+      element = $compile(
+        '<div>' +
+        '  <div ng-repeat="item in items | filter:x as foo=6 track by $index">{{item}}</div>' +
+        '</div>')(scope);
+      expect($exceptionHandler.errors.shift()[0].message).
+        toMatch(/^\[ngRepeat:nonassign\] Expected collection alias to be an assignable expression but got \'foo=6\'\./);
+      dealoc(element);
+
+      element = $compile(
+        '<div>' +
+        '  <div ng-repeat="item in items | filter:x as foo = 6 track by $index">{{item}}</div>' +
+        '</div>')(scope);
+      expect($exceptionHandler.errors.shift()[0].message).
+        toMatch(/^\[ngRepeat:nonassign\] Expected collection alias to be an assignable expression but got \'foo = 6\'\./);
+    }));
   });