fix($animate): only block keyframes if a stagger is set to occur

Transitions must be blocked so that the initial CSS class can be applied
without triggering an animation. Keyframes do not need to be blocked since
animations are always triggered on the starting CSS class, however, if a
stagger animation is set to occur then all elements for index > 0 should
be blocked. This is to prevent the animation from occuring early on before
the stagger delay for the given element has passed.

With ngAnimate and keyframe animations, IE10 and Safari will render a slight
flicker effect caused by the blocking. This fix resolves this issue.

Closes angular#4225

src/ngAnimate/animate.js

@@ -1247,7 +1247,11 @@ angular.module('ngAnimate', ['ng'])
         if(transitionDuration > 0) {
           blockTransitions(element, className, isCurrentlyAnimating);
         }
-        if(animationDuration > 0) {
+
+        //keyframes don't need to be blocked unless staggered and if a stagger
+        //is present then only the items that are of current index > 0 are blocked (since
+        //the element at index==0 will never have a stagger delay at all).
+        if(animationDuration > 0 && stagger.animationDelay > 0 && stagger.animationDuration === 0) {
           blockKeyframeAnimations(element);
         }
 

test/ngAnimate/animateSpec.js

@@ -841,6 +841,49 @@ describe("ngAnimate", function() {
           }));
 
 
+          it("should block and unblock keyframe animations when a stagger animation kicks in while skipping the first element",
+            inject(function($animate, $rootScope, $compile, $sniffer, $timeout, $document, $rootElement) {
+
+            if(!$sniffer.animations) return;
+
+            $animate.enabled(true);
+
+            ss.addRule('.blocked-animation.ng-enter',
+              '-webkit-animation:my_animation 1s;' +
+              'animation:my_animation 1s;');
+
+            ss.addRule('.blocked-animation.ng-enter-stagger',
+              '-webkit-animation-delay:0.2s;' +
+              'animation-delay:0.2s;');
+
+            var container = $compile(html('<div></div>'))($rootScope);
+
+            var elements = [];
+            for(var i = 0; i < 4; i++) {
+              var newScope = $rootScope.$new();
+              var element = $compile('<div class="blocked-animation"></div>')(newScope);
+              $animate.enter(element, container);
+              elements.push(element);
+            };
+
+            $rootScope.$digest();
+
+            expect(elements[0].attr('style')).toBeFalsy();
+            expect(elements[1].attr('style')).toMatch(/animation:.+?none/);
+            expect(elements[2].attr('style')).toMatch(/animation:.+?none/);
+            expect(elements[3].attr('style')).toMatch(/animation:.+?none/);
+
+            $animate.triggerReflow();
+
+            expect(elements[0].attr('style')).toBeFalsy();
+            expect(elements[1].attr('style')).not.toMatch(/animation:.+?none/);
+            expect(elements[1].attr('style')).toMatch(/animation-delay: 0.2\d*s/);
+            expect(elements[2].attr('style')).not.toMatch(/animation:.+?none/);
+            expect(elements[2].attr('style')).toMatch(/animation-delay: 0.4\d*s/);
+            expect(elements[3].attr('style')).not.toMatch(/animation:.+?none/);
+            expect(elements[3].attr('style')).toMatch(/animation-delay: 0.6\d*s/);
+          }));
+
           it("should stagger items when multiple animation durations/delays are defined",
             inject(function($animate, $rootScope, $compile, $sniffer, $timeout, $document, $rootElement) {
 
@@ -3013,7 +3056,7 @@ describe("ngAnimate", function() {
     }));
 
 
-    it('should block and unblock keyframe animations around the reflow operation',
+    it('should not block keyframe animations around the reflow operation',
       inject(function($rootScope, $compile, $rootElement, $document, $animate, $sniffer, $timeout) {
 
       if (!$sniffer.animations) return;
@@ -3032,15 +3075,19 @@ describe("ngAnimate", function() {
 
       $animate.addClass(element, 'trigger-class');
 
-      expect(node.style[animationKey]).toContain('none');
+      expect(node.style[animationKey]).not.toContain('none');
 
       $animate.triggerReflow();
 
       expect(node.style[animationKey]).not.toContain('none');
+
+      browserTrigger(element, 'animationend', { timeStamp: Date.now() + 1000, elapsedTime: 1 });
+
+      expect(node.style[animationKey]).not.toContain('none');
     }));
 
 
-    it('should block and unblock keyframe animations before the followup JS animation occurs', function() {
+    it('should not block keyframe animations at anytime before a followup JS animation occurs', function() {
       module(function($animateProvider) {
         $animateProvider.register('.special', function($sniffer, $window) {
           var prop = $sniffer.vendorPrefix == 'Webkit' ? 'WebkitAnimation' : 'animation';
@@ -3076,8 +3123,8 @@ describe("ngAnimate", function() {
 
         var prop = $sniffer.vendorPrefix == 'Webkit' ? 'WebkitAnimation' : 'animation';
 
-        expect(element[0].style[prop]).toContain('none');
-        expect($window.getComputedStyle(element[0])[prop + 'Duration']).toBe('0s');
+        expect(element[0].style[prop]).not.toContain('none');
+        expect($window.getComputedStyle(element[0])[prop + 'Duration']).toBe('1s');
 
         $animate.triggerReflow();
       });