fix($parse): Copy inputs for expressions with expensive checks

Closes: #13871

src/ng/parse.js

@@ -1797,6 +1797,7 @@ function $ParseProvider() {
       for (var i = 0; fn.inputs && i < fn.inputs.length; ++i) {
         fn.inputs[i] = expensiveChecksInterceptor(fn.inputs[i]);
       }
+      expensiveCheckFn.inputs = fn.inputs;
 
       return expensiveCheckFn;
 

test/ng/parseSpec.js

@@ -2429,6 +2429,13 @@ describe('parser', function() {
                 expect($parse.$$runningExpensiveChecks()).toEqual(false);
               });
             });
+
+            it('should handle `inputs` when running with expensive checks', inject(function($parse) {
+              expect(function() {
+                scope.$watch($parse('a + b', null, true), noop);
+                scope.$digest();
+              }).not.toThrow();
+            }));
           });
         });