feat($parse): allow watching array/object of inputs to literal values

The inputs of array/object literals are now watched for changes.
If the an input changes then a new instance of the literal will be
provided when the parsed expression is executed.

Closes #15301

Author: jbedard

src/ng/parse.js

@@ -1782,13 +1782,13 @@ function $ParseProvider() {
       }
     }
 
-    function expressionInputDirtyCheck(newValue, oldValueOfValue) {
+    function expressionInputDirtyCheck(newValue, oldValueOfValue, compareObjectIdentity) {
 
       if (newValue == null || oldValueOfValue == null) { // null/undefined
         return newValue === oldValueOfValue;
       }
 
-      if (typeof newValue === 'object') {
+      if (typeof newValue === 'object' && !compareObjectIdentity) {
 
         // attempt to convert the value to a primitive type
         // TODO(docs): add a note to docs that by implementing valueOf even objects and arrays can
@@ -1817,7 +1817,7 @@ function $ParseProvider() {
         inputExpressions = inputExpressions[0];
         return scope.$watch(function expressionInputWatch(scope) {
           var newInputValue = inputExpressions(scope);
-          if (!expressionInputDirtyCheck(newInputValue, oldInputValueOf)) {
+          if (!expressionInputDirtyCheck(newInputValue, oldInputValueOf, parsedExpression.literal)) {
             lastResult = parsedExpression(scope, undefined, undefined, [newInputValue]);
             oldInputValueOf = newInputValue && getValueOf(newInputValue);
           }
@@ -1837,7 +1837,7 @@ function $ParseProvider() {
 
         for (var i = 0, ii = inputExpressions.length; i < ii; i++) {
           var newInputValue = inputExpressions[i](scope);
-          if (changed || (changed = !expressionInputDirtyCheck(newInputValue, oldInputValueOfValues[i]))) {
+          if (changed || (changed = !expressionInputDirtyCheck(newInputValue, oldInputValueOfValues[i], parsedExpression.literal))) {
             oldInputValues[i] = newInputValue;
             oldInputValueOfValues[i] = newInputValue && getValueOf(newInputValue);
           }

test/ng/parseSpec.js

@@ -3118,6 +3118,74 @@ describe('parser', function() {
           scope.$digest();
           expect(objB.value).toBe(scope.input);
         }));
+
+        it('should support watching literals', inject(function($parse) {
+          var lastVal = NaN;
+          var callCount = 0;
+          var listener = function(val) { callCount++; lastVal = val; };
+
+          scope.$watch('{val: val}', listener);
+
+          scope.$apply('val = 1');
+          expect(callCount).toBe(1);
+          expect(lastVal).toEqual({val: 1});
+
+          scope.$apply('val = []');
+          expect(callCount).toBe(2);
+          expect(lastVal).toEqual({val: []});
+
+          scope.$apply('val = []');
+          expect(callCount).toBe(3);
+          expect(lastVal).toEqual({val: []});
+
+          scope.$apply('val = {}');
+          expect(callCount).toBe(4);
+          expect(lastVal).toEqual({val: {}});
+        }));
+
+        it('should only watch the direct inputs to literals', inject(function($parse) {
+          var lastVal = NaN;
+          var callCount = 0;
+          var listener = function(val) { callCount++; lastVal = val; };
+
+          scope.$watch('{val: val}', listener);
+
+          scope.$apply('val = 1');
+          expect(callCount).toBe(1);
+          expect(lastVal).toEqual({val: 1});
+
+          scope.$apply('val = [2]');
+          expect(callCount).toBe(2);
+          expect(lastVal).toEqual({val: [2]});
+
+          scope.$apply('val.push(3)');
+          expect(callCount).toBe(2);
+
+          scope.$apply('val.length = 0');
+          expect(callCount).toBe(2);
+        }));
+
+        it('should only watch the direct inputs to nested literals', inject(function($parse) {
+          var lastVal = NaN;
+          var callCount = 0;
+          var listener = function(val) { callCount++; lastVal = val; };
+
+          scope.$watch('[{val: [val]}]', listener);
+
+          scope.$apply('val = 1');
+          expect(callCount).toBe(1);
+          expect(lastVal).toEqual([{val: [1]}]);
+
+          scope.$apply('val = [2]');
+          expect(callCount).toBe(2);
+          expect(lastVal).toEqual([{val: [[2]]}]);
+
+          scope.$apply('val.push(3)');
+          expect(callCount).toBe(2);
+
+          scope.$apply('val.length = 0');
+          expect(callCount).toBe(2);
+        }));
       });
 
       describe('locals', function() {