fix($parse): evaluate once simple expressions in interpolations

For simple expressions without filters that have a stateless interceptor
then handle the 2nd phase parse evaluation using `inputs`.

This fixes the issue that interpolated simple expressions were evaluated twice
within one digest loop.

Closes angular#12983

Author: lgalfaso

src/ng/parse.js

@@ -1906,13 +1906,14 @@ function $ParseProvider() {
     function addInterceptor(parsedExpression, interceptorFn) {
       if (!interceptorFn) return parsedExpression;
       var watchDelegate = parsedExpression.$$watchDelegate;
+      var useInputs = false;
 
       var regularWatch =
           watchDelegate !== oneTimeLiteralWatchDelegate &&
           watchDelegate !== oneTimeWatchDelegate;
 
       var fn = regularWatch ? function regularInterceptedExpression(scope, locals, assign, inputs) {
-        var value = parsedExpression(scope, locals, assign, inputs);
+        var value = useInputs && inputs ? inputs[0] : parsedExpression(scope, locals, assign, inputs);
         return interceptorFn(value, scope, locals);
       } : function oneTimeInterceptedExpression(scope, locals, assign, inputs) {
         var value = parsedExpression(scope, locals, assign, inputs);
@@ -1930,6 +1931,7 @@ function $ParseProvider() {
         // If there is an interceptor, but no watchDelegate then treat the interceptor like
         // we treat filters - it is assumed to be a pure function unless flagged with $stateful
         fn.$$watchDelegate = inputsWatchDelegate;
+        useInputs = !parsedExpression.inputs;
         fn.inputs = parsedExpression.inputs ? parsedExpression.inputs : [parsedExpression];
       }
 

test/ng/compileSpec.js

@@ -947,6 +947,14 @@ describe('$compile', function() {
           expect(child).toHaveClass('log'); // merged from replace directive template
         }));
 
+        it('should interpolate the values once per digest',
+            inject(function($compile, $rootScope, log) {
+          element = $compile('<div>{{log("A")}} foo {{::log("B")}}</div>')($rootScope);
+          $rootScope.log = log;
+          $rootScope.$digest();
+          expect(log).toEqual('A; B; A; B');
+        }));
+
         it('should update references to replaced jQuery context', function() {
           module(function($compileProvider) {
             $compileProvider.directive('foo', function() {