Add dispatchEvent to fragment instances (#32813)

`fragmentInstance.dispatchEvent(evt)` calls `element.dispatchEvent(evt)`
on the fragment's host parent. This mimics bubbling if the
`fragmentInstance` could receive an event itself.

If the parent is disconnected, there is a dev warning and no event is
dispatched.

fixtures/dom/src/components/fixtures/fragment-refs/EventDispatchCase.js

@@ -0,0 +1,157 @@
+import TestCase from '../../TestCase';
+import Fixture from '../../Fixture';
+
+const React = window.React;
+const {Fragment, useRef, useState} = React;
+
+function WrapperComponent(props) {
+  return props.children;
+}
+
+const initialState = {
+  child: false,
+  parent: false,
+  grandparent: false,
+};
+
+export default function EventListenerCase() {
+  const fragmentRef = useRef(null);
+  const [clickedState, setClickedState] = useState({...initialState});
+  const [fragmentEventFired, setFragmentEventFired] = useState(false);
+  const [bubblesState, setBubblesState] = useState(true);
+
+  function setClick(id) {
+    setClickedState(prev => ({...prev, [id]: true}));
+  }
+
+  function fragmentClickHandler(e) {
+    setFragmentEventFired(true);
+  }
+
+  return (
+    <TestCase title="Event Dispatch">
+      <TestCase.Steps>
+        <li>
+          Each box has regular click handlers, you can click each one to observe
+          the status changing through standard bubbling.
+        </li>
+        <li>Clear the clicked state</li>
+        <li>
+          Click the "Dispatch click event" button to dispatch a click event on
+          the Fragment. The event will be dispatched on the Fragment's parent,
+          so the child will not change state.
+        </li>
+        <li>
+          Click the "Add event listener" button to add a click event listener on
+          the Fragment. This registers a handler that will turn the child blue
+          on click.
+        </li>
+        <li>
+          Now click the "Dispatch click event" button again. You can see that it
+          will fire the Fragment's event handler in addition to bubbling the
+          click from the parent.
+        </li>
+        <li>
+          If you turn off bubbling, only the Fragment's event handler will be
+          called.
+        </li>
+      </TestCase.Steps>
+
+      <TestCase.ExpectedResult>
+        <p>
+          Dispatching an event on a Fragment will forward the dispatch to its
+          parent for the standard case. You can observe when dispatching that
+          the parent handler is called in additional to bubbling from there. A
+          delay is added to make the bubbling more clear.{' '}
+        </p>
+        <p>
+          When there have been event handlers added to the Fragment, the
+          Fragment's event handler will be called in addition to bubbling from
+          the parent. Without bubbling, only the Fragment's event handler will
+          be called.
+        </p>
+      </TestCase.ExpectedResult>
+
+      <Fixture>
+        <Fixture.Controls>
+          <select
+            value={bubblesState ? 'true' : 'false'}
+            onChange={e => {
+              setBubblesState(e.target.value === 'true');
+            }}>
+            <option value="true">Bubbles: true</option>
+            <option value="false">Bubbles: false</option>
+          </select>
+          <button
+            onClick={() => {
+              fragmentRef.current.dispatchEvent(
+                new MouseEvent('click', {bubbles: bubblesState})
+              );
+            }}>
+            Dispatch click event
+          </button>
+          <button
+            onClick={() => {
+              setClickedState({...initialState});
+              setFragmentEventFired(false);
+            }}>
+            Reset clicked state
+          </button>
+          <button
+            onClick={() => {
+              fragmentRef.current.addEventListener(
+                'click',
+                fragmentClickHandler
+              );
+            }}>
+            Add event listener
+          </button>
+          <button
+            onClick={() => {
+              fragmentRef.current.removeEventListener(
+                'click',
+                fragmentClickHandler
+              );
+            }}>
+            Remove event listener
+          </button>
+        </Fixture.Controls>
+        <div
+          id="grandparent"
+          onClick={e => {
+            setTimeout(() => {
+              setClick('grandparent');
+            }, 200);
+          }}
+          className="card">
+          Fragment grandparent - clicked:{' '}
+          {clickedState.grandparent ? 'true' : 'false'}
+          <div
+            id="parent"
+            onClick={e => {
+              setTimeout(() => {
+                setClick('parent');
+              }, 100);
+            }}
+            className="card">
+            Fragment parent - clicked: {clickedState.parent ? 'true' : 'false'}
+            <Fragment ref={fragmentRef}>
+              <div
+                style={{
+                  backgroundColor: fragmentEventFired ? 'lightblue' : 'inherit',
+                }}
+                id="child"
+                className="card"
+                onClick={e => {
+                  setClick('child');
+                }}>
+                Fragment child - clicked:{' '}
+                {clickedState.child ? 'true' : 'false'}
+              </div>
+            </Fragment>
+          </div>
+        </div>
+      </Fixture>
+    </TestCase>
+  );
+}

fixtures/dom/src/components/fixtures/fragment-refs/index.js

@@ -1,5 +1,6 @@
 import FixtureSet from '../../FixtureSet';
 import EventListenerCase from './EventListenerCase';
+import EventDispatchCase from './EventDispatchCase';
 import IntersectionObserverCase from './IntersectionObserverCase';
 import ResizeObserverCase from './ResizeObserverCase';
 import FocusCase from './FocusCase';
@@ -11,6 +12,7 @@ export default function FragmentRefsPage() {
   return (
     <FixtureSet title="Fragment Refs">
       <EventListenerCase />
+      <EventDispatchCase />
       <IntersectionObserverCase />
       <ResizeObserverCase />
       <FocusCase />

packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js

@@ -2598,6 +2598,7 @@ export type FragmentInstanceType = {
     listener: EventListener,
     optionsOrUseCapture?: EventListenerOptionsOrUseCapture,
   ): void,
+  dispatchEvent(event: Event): boolean,
   focus(focusOptions?: FocusOptions): void,
   focusLast(focusOptions?: FocusOptions): void,
   blur(): void,
@@ -2695,6 +2696,43 @@ function removeEventListenerFromChild(
   return false;
 }
 // $FlowFixMe[prop-missing]
+FragmentInstance.prototype.dispatchEvent = function (
+  this: FragmentInstanceType,
+  event: Event,
+): boolean {
+  const parentHostFiber = getFragmentParentHostFiber(this._fragmentFiber);
+  if (parentHostFiber === null) {
+    return true;
+  }
+  const parentHostInstance =
+    getInstanceFromHostFiber<Instance>(parentHostFiber);
+  const eventListeners = this._eventListeners;
+  if (
+    (eventListeners !== null && eventListeners.length > 0) ||
+    !event.bubbles
+  ) {
+    const temp = document.createTextNode('');
+    if (eventListeners) {
+      for (let i = 0; i < eventListeners.length; i++) {
+        const {type, listener, optionsOrUseCapture} = eventListeners[i];
+        temp.addEventListener(type, listener, optionsOrUseCapture);
+      }
+    }
+    parentHostInstance.appendChild(temp);
+    const cancelable = temp.dispatchEvent(event);
+    if (eventListeners) {
+      for (let i = 0; i < eventListeners.length; i++) {
+        const {type, listener, optionsOrUseCapture} = eventListeners[i];
+        temp.removeEventListener(type, listener, optionsOrUseCapture);
+      }
+    }
+    parentHostInstance.removeChild(temp);
+    return cancelable;
+  } else {
+    return parentHostInstance.dispatchEvent(event);
+  }
+};
+// $FlowFixMe[prop-missing]
 FragmentInstance.prototype.focus = function (
   this: FragmentInstanceType,
   focusOptions?: FocusOptions,