[BUGFIX beta] support mouseEnter/Leave events w/o jQuery

As these events don't bubble, the `EventDispatcher`'s event delegation approach does not work here, when not using jQuery. jQuery has special handling of these events, by listening to `mouseover`/`mouseout` instead and dispatching fake `mouseenter`/`mouseleave` events. This adds similar handling to `EventDispatcher`'s native mode for these events.

Fixes #16591

packages/ember-glimmer/tests/integration/event-dispatcher-test.js

@@ -146,6 +146,56 @@ moduleFor(
 
       this.$('#is-done').trigger('click');
     }
+
+    ['@test delegated event listeners work for mouseEnter/Leave'](assert) {
+      let receivedEnterEvents = [];
+      let receivedLeaveEvents = [];
+
+      this.registerComponent('x-foo', {
+        ComponentClass: Component.extend({
+          mouseEnter(event) {
+            receivedEnterEvents.push(event);
+          },
+          mouseLeave(event) {
+            receivedLeaveEvents.push(event);
+          },
+        }),
+        template: `<div id="inner"></div>`,
+      });
+
+      this.render(`{{x-foo id="outer"}}`);
+
+      let parent = this.element;
+      let outer = this.$('#outer')[0];
+
+      // mouse moves over #outer
+      this.runTask(() => {
+        this.$('#outer').trigger('mouseenter', { canBubble: false, relatedTarget: parent });
+        this.$('#outer').trigger('mouseover', { relatedTarget: parent });
+      });
+      assert.equal(receivedEnterEvents.length, 1, 'mouseenter event was triggered');
+      assert.strictEqual(receivedEnterEvents[0].target, outer);
+
+      // mouse moves over #inner
+      this.runTask(() => {
+        this.$('#inner').trigger('mouseover', { relatedTarget: outer });
+      });
+      assert.equal(receivedEnterEvents.length, 1, 'mouseenter event was not triggered again');
+
+      // mouse moves out of #inner
+      this.runTask(() => {
+        this.$('#inner').trigger('mouseout', { relatedTarget: outer });
+      });
+      assert.equal(receivedLeaveEvents.length, 0, 'mouseleave event was not triggered');
+
+      // mouse moves out of #outer
+      this.runTask(() => {
+        this.$('#outer').trigger('mouseleave', { canBubble: false, relatedTarget: parent });
+        this.$('#outer').trigger('mouseout', { relatedTarget: parent });
+      });
+      assert.equal(receivedLeaveEvents.length, 1, 'mouseleave event was triggered');
+      assert.strictEqual(receivedLeaveEvents[0].target, outer);
+    }
   }
 );
 

packages/ember-views/lib/system/event_dispatcher.js

@@ -15,6 +15,11 @@ import addJQueryEventDeprecation from './jquery_event_deprecation';
 const ROOT_ELEMENT_CLASS = 'ember-application';
 const ROOT_ELEMENT_SELECTOR = `.${ROOT_ELEMENT_CLASS}`;
 
+const EVENT_MAP = {
+  mouseenter: 'mouseover',
+  mouseleave: 'mouseout',
+};
+
 /**
   `Ember.EventDispatcher` handles delegating browser events to their
   corresponding `Ember.Views.` For example, when you click on a view,
@@ -290,27 +295,86 @@ export default EmberObject.extend({
         }
       };
 
-      let handleEvent = (this._eventHandlers[event] = event => {
-        let target = event.target;
+      // Special handling of events that don't bubble, so event delegation does not work.
+      // Mimics the way this is handled in jQuery,
+      // see https://github.com/jquery/jquery/blob/899c56f6ada26821e8af12d9f35fa039100e838e/src/event.js#L666-L700
+      if (EVENT_MAP[event] !== undefined) {
+        let mappedEventType = EVENT_MAP[event];
+        let origEventType = event;
+
+        let createFakeEvent = (eventType, event) => {
+          let fakeEvent = document.createEvent('MouseEvent');
+          fakeEvent.initMouseEvent(
+            eventType,
+            false,
+            false,
+            event.view,
+            event.detail,
+            event.screenX,
+            event.screenY,
+            event.clientX,
+            event.clientY,
+            event.ctrlKey,
+            event.altKey,
+            event.shiftKey,
+            event.metaKey,
+            event.button,
+            event.relatedTarget
+          );
+
+          // fake event.target as we don't dispatch the event
+          Object.defineProperty(fakeEvent, 'target', { value: event.target, enumerable: true });
+
+          return fakeEvent;
+        };
+
+        let handleMappedEvent = (this._eventHandlers[mappedEventType] = event => {
+          let target = event.target;
+          let related = event.relatedTarget;
 
-        do {
-          if (viewRegistry[target.id]) {
-            if (viewHandler(target, event) === false) {
-              event.preventDefault();
-              event.stopPropagation();
+          do {
+            // For mouseenter/leave call the handler if related is outside the target.
+            // No relatedTarget if the mouse left/entered the browser window
+            if (viewRegistry[target.id]) {
+              if (!related || (related !== target && !target.contains(related))) {
+                viewHandler(target, createFakeEvent(origEventType, event));
+              }
               break;
-            }
-          } else if (target.hasAttribute('data-ember-action')) {
-            if (actionHandler(target, event) === false) {
+            } else if (target.hasAttribute('data-ember-action')) {
+              if (!related || (related !== target && !target.contains(related))) {
+                actionHandler(target, createFakeEvent(origEventType, event));
+              }
               break;
             }
-          }
 
-          target = target.parentNode;
-        } while (target && target.nodeType === 1);
-      });
+            target = target.parentNode;
+          } while (target && target.nodeType === 1);
+        });
+
+        rootElement.addEventListener(mappedEventType, handleMappedEvent);
+      } else {
+        let handleEvent = (this._eventHandlers[event] = event => {
+          let target = event.target;
+
+          do {
+            if (viewRegistry[target.id]) {
+              if (viewHandler(target, event) === false) {
+                event.preventDefault();
+                event.stopPropagation();
+                break;
+              }
+            } else if (target.hasAttribute('data-ember-action')) {
+              if (actionHandler(target, event) === false) {
+                break;
+              }
+            }
 
-      rootElement.addEventListener(event, handleEvent);
+            target = target.parentNode;
+          } while (target && target.nodeType === 1);
+        });
+
+        rootElement.addEventListener(event, handleEvent);
+      }
     } else {
       rootElement.on(`${event}.ember`, '.ember-view', function(evt) {
         let view = viewRegistry[this.id];