Selective Hydration

packages/react-dom/src/__tests__/ReactDOMServerSelectiveHydration-test.internal.js

@@ -0,0 +1,117 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails react-core
+ */
+
+'use strict';
+
+let React;
+let ReactDOM;
+let ReactDOMServer;
+let Scheduler;
+let ReactFeatureFlags;
+let Suspense;
+
+function dispatchClickEvent(target) {
+  const mouseOutEvent = document.createEvent('MouseEvents');
+  mouseOutEvent.initMouseEvent(
+    'click',
+    true,
+    true,
+    window,
+    0,
+    50,
+    50,
+    50,
+    50,
+    false,
+    false,
+    false,
+    false,
+    0,
+    target,
+  );
+  return target.dispatchEvent(mouseOutEvent);
+}
+
+describe('ReactDOMServerSelectiveHydration', () => {
+  beforeEach(() => {
+    jest.resetModuleRegistry();
+
+    ReactFeatureFlags = require('shared/ReactFeatureFlags');
+    ReactFeatureFlags.enableSuspenseServerRenderer = true;
+    ReactFeatureFlags.enableSelectiveHydration = true;
+
+    React = require('react');
+    ReactDOM = require('react-dom');
+    ReactDOMServer = require('react-dom/server');
+    Scheduler = require('scheduler');
+    Suspense = React.Suspense;
+  });
+
+  it('hydrates the target boundary synchronously during a click', async () => {
+    function Child({text}) {
+      Scheduler.unstable_yieldValue(text);
+      return (
+        <span
+          onClick={e => {
+            e.preventDefault();
+            Scheduler.unstable_yieldValue('Clicked ' + text);
+          }}>
+          {text}
+        </span>
+      );
+    }
+
+    function App() {
+      Scheduler.unstable_yieldValue('App');
+      return (
+        <div>
+          <Suspense fallback="Loading...">
+            <Child text="A" />
+          </Suspense>
+          <Suspense fallback="Loading...">
+            <Child text="B" />
+          </Suspense>
+        </div>
+      );
+    }
+
+    let finalHTML = ReactDOMServer.renderToString(<App />);
+
+    expect(Scheduler).toHaveYielded(['App', 'A', 'B']);
+
+    let container = document.createElement('div');
+    // We need this to be in the document since we'll dispatch events on it.
+    document.body.appendChild(container);
+
+    container.innerHTML = finalHTML;
+
+    let span = container.getElementsByTagName('span')[1];
+
+    let root = ReactDOM.unstable_createRoot(container, {hydrate: true});
+    root.render(<App />);
+
+    // Nothing has been hydrated so far.
+    expect(Scheduler).toHaveYielded([]);
+
+    // This should synchronously hydrate the root App and the second suspense
+    // boundary.
+    let result = dispatchClickEvent(span);
+
+    // The event should have been canceled because we called preventDefault.
+    expect(result).toBe(false);
+
+    // We rendered App, B and then invoked the event without rendering A.
+    expect(Scheduler).toHaveYielded(['App', 'B', 'Clicked B']);
+
+    // After continuing the scheduler, we finally hydrate A.
+    expect(Scheduler).toFlushAndYield(['A']);
+
+    document.body.removeChild(container);
+  });
+});

packages/react-dom/src/client/ReactDOM.js

@@ -39,6 +39,7 @@ import {
   findHostInstanceWithWarning,
   flushPassiveEffects,
   IsThisRendererActing,
+  attemptSynchronousHydration,
 } from 'react-reconciler/inline.dom';
 import {createPortal as createPortalImpl} from 'shared/ReactPortal';
 import {canUseDOM} from 'shared/ExecutionEnvironment';
@@ -74,6 +75,7 @@ import {
 } from './ReactDOMComponentTree';
 import {restoreControlledState} from './ReactDOMComponent';
 import {dispatchEvent} from '../events/ReactDOMEventListener';
+import {setAttemptSynchronousHydration} from '../events/ReactDOMEventReplaying';
 import {eagerlyTrapReplayableEvents} from '../events/ReactDOMEventReplaying';
 import {
   ELEMENT_NODE,
@@ -83,6 +85,8 @@ import {
 } from '../shared/HTMLNodeType';
 import {ROOT_ATTRIBUTE_NAME} from '../shared/DOMProperty';
 
+setAttemptSynchronousHydration(attemptSynchronousHydration);
+
 const ReactCurrentOwner = ReactSharedInternals.ReactCurrentOwner;
 
 let topLevelUpdateWarnings;

packages/react-dom/src/client/ReactDOMComponentTree.js

@@ -5,7 +5,12 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {HostComponent, HostText} from 'shared/ReactWorkTags';
+import {
+  HostComponent,
+  HostText,
+  HostRoot,
+  SuspenseComponent,
+} from 'shared/ReactWorkTags';
 import invariant from 'shared/invariant';
 
 import {getParentSuspenseInstance} from './ReactDOMHostConfig';
@@ -112,9 +117,14 @@ export function getClosestInstanceFromNode(targetNode) {
  * instance, or null if the node was not rendered by this React.
  */
 export function getInstanceFromNode(node) {
-  const inst = node[internalInstanceKey];
+  const inst = node[internalInstanceKey] || node[internalContainerInstanceKey];
   if (inst) {
-    if (inst.tag === HostComponent || inst.tag === HostText) {
+    if (
+      inst.tag === HostComponent ||
+      inst.tag === HostText ||
+      inst.tag === SuspenseComponent ||
+      inst.tag === HostRoot
+    ) {
       return inst;
     } else {
       return null;

packages/react-dom/src/events/ReactDOMEventReplaying.js

@@ -12,7 +12,10 @@ import type {Container, SuspenseInstance} from '../client/ReactDOMHostConfig';
 import type {DOMTopLevelEventType} from 'legacy-events/TopLevelEventTypes';
 import type {EventSystemFlags} from 'legacy-events/EventSystemFlags';
 
-import {enableFlareAPI} from 'shared/ReactFeatureFlags';
+import {
+  enableFlareAPI,
+  enableSelectiveHydration,
+} from 'shared/ReactFeatureFlags';
 import {
   unstable_scheduleCallback as scheduleCallback,
   unstable_NormalPriority as NormalPriority,
@@ -25,8 +28,15 @@ import {
   getListeningSetForElement,
   listenToTopLevel,
 } from './ReactBrowserEventEmitter';
+import {getInstanceFromNode} from '../client/ReactDOMComponentTree';
 import {unsafeCastDOMTopLevelTypeToString} from 'legacy-events/TopLevelEventTypes';
 
+let attemptSynchronousHydration: (fiber: Object) => void;
+
+export function setAttemptSynchronousHydration(fn: (fiber: Object) => void) {
+  attemptSynchronousHydration = fn;
+}
+
 // TODO: Upgrade this definition once we're on a newer version of Flow that
 // has this definition built-in.
 type PointerEvent = Event & {
@@ -223,18 +233,36 @@ export function queueDiscreteEvent(
   eventSystemFlags: EventSystemFlags,
   nativeEvent: AnyNativeEvent,
 ): void {
-  queuedDiscreteEvents.push(
-    createQueuedReplayableEvent(
-      blockedOn,
-      topLevelType,
-      eventSystemFlags,
-      nativeEvent,
-    ),
+  const queuedEvent = createQueuedReplayableEvent(
+    blockedOn,
+    topLevelType,
+    eventSystemFlags,
+    nativeEvent,
   );
-  if (blockedOn === null && queuedDiscreteEvents.length === 1) {
-    // This probably shouldn't happen but some defensive coding might
-    // help us get unblocked if we have a bug.
-    replayUnblockedEvents();
+  queuedDiscreteEvents.push(queuedEvent);
+  if (enableSelectiveHydration) {
+    if (queuedDiscreteEvents.length === 1) {
+      // If this was the first discrete event, we might be able to
+      // synchronously unblock it so that preventDefault still works.
+      while (queuedEvent.blockedOn !== null) {
+        let fiber = getInstanceFromNode(queuedEvent.blockedOn);
+        if (fiber === null) {
+          break;
+        }
+        attemptSynchronousHydration(fiber);
+        if (queuedEvent.blockedOn === null) {
+          // We got unblocked by hydration. Let's try again.
+          replayUnblockedEvents();
+          // If we're reblocked, on an inner boundary, we might need
+          // to attempt hydrating that one.
+          continue;
+        } else {
+          // We're still blocked from hydation, we have to give up
+          // and replay later.
+          break;
+        }
+      }
+    }
   }
 }
 

packages/react-reconciler/src/ReactFiberReconciler.js

@@ -27,7 +27,12 @@ import {
   findCurrentHostFiberWithNoPortals,
 } from 'react-reconciler/reflection';
 import {get as getInstance} from 'shared/ReactInstanceMap';
-import {HostComponent, ClassComponent} from 'shared/ReactWorkTags';
+import {
+  HostComponent,
+  ClassComponent,
+  HostRoot,
+  SuspenseComponent,
+} from 'shared/ReactWorkTags';
 import getComponentName from 'shared/getComponentName';
 import invariant from 'shared/invariant';
 import warningWithoutStack from 'shared/warningWithoutStack';
@@ -362,6 +367,21 @@ export function getPublicRootInstance(
   }
 }
 
+export function attemptSynchronousHydration(fiber: Fiber): void {
+  switch (fiber.tag) {
+    case HostRoot:
+      let root: FiberRoot = fiber.stateNode;
+      if (root.hydrate) {
+        // Flush the first scheduled "update".
+        flushRoot(root, root.firstPendingTime);
+      }
+      break;
+    case SuspenseComponent:
+      flushSync(() => scheduleWork(fiber, Sync));
+      break;
+  }
+}
+
 export {findHostInstance};
 
 export {findHostInstanceWithWarning};

packages/shared/ReactFeatureFlags.js

@@ -33,6 +33,7 @@ export const enableSchedulerTracing = __PROFILE__;
 
 // Only used in www builds.
 export const enableSuspenseServerRenderer = false; // TODO: __DEV__? Here it might just be false.
+export const enableSelectiveHydration = false;
 
 // Only used in www builds.
 export const enableSchedulerDebugging = false;

packages/shared/forks/ReactFeatureFlags.native-fb.js

@@ -22,6 +22,7 @@ export const enableUserTimingAPI = __DEV__;
 export const enableProfilerTimer = __PROFILE__;
 export const enableSchedulerTracing = __PROFILE__;
 export const enableSuspenseServerRenderer = false;
+export const enableSelectiveHydration = false;
 export const enableStableConcurrentModeAPIs = false;
 export const warnAboutShorthandPropertyCollision = false;
 export const enableSchedulerDebugging = false;

packages/shared/forks/ReactFeatureFlags.native-oss.js

@@ -20,6 +20,7 @@ export const warnAboutDeprecatedLifecycles = true;
 export const enableProfilerTimer = __PROFILE__;
 export const enableSchedulerTracing = __PROFILE__;
 export const enableSuspenseServerRenderer = false;
+export const enableSelectiveHydration = false;
 export const disableJavaScriptURLs = false;
 export const disableInputAttributeSyncing = false;
 export const enableStableConcurrentModeAPIs = false;

packages/shared/forks/ReactFeatureFlags.persistent.js

@@ -20,6 +20,7 @@ export const replayFailedUnitOfWorkWithInvokeGuardedCallback = __DEV__;
 export const enableProfilerTimer = __PROFILE__;
 export const enableSchedulerTracing = __PROFILE__;
 export const enableSuspenseServerRenderer = false;
+export const enableSelectiveHydration = false;
 export const disableJavaScriptURLs = false;
 export const disableInputAttributeSyncing = false;
 export const enableStableConcurrentModeAPIs = false;

packages/shared/forks/ReactFeatureFlags.test-renderer.js

@@ -20,6 +20,7 @@ export const replayFailedUnitOfWorkWithInvokeGuardedCallback = false;
 export const enableProfilerTimer = __PROFILE__;
 export const enableSchedulerTracing = __PROFILE__;
 export const enableSuspenseServerRenderer = false;
+export const enableSelectiveHydration = false;
 export const disableJavaScriptURLs = false;
 export const disableInputAttributeSyncing = false;
 export const enableStableConcurrentModeAPIs = false;

packages/shared/forks/ReactFeatureFlags.test-renderer.www.js

@@ -20,6 +20,7 @@ export const replayFailedUnitOfWorkWithInvokeGuardedCallback = false;
 export const enableProfilerTimer = __PROFILE__;
 export const enableSchedulerTracing = __PROFILE__;
 export const enableSuspenseServerRenderer = false;
+export const enableSelectiveHydration = false;
 export const enableStableConcurrentModeAPIs = false;
 export const enableSchedulerDebugging = false;
 export const warnAboutDeprecatedSetNativeProps = false;

packages/shared/forks/ReactFeatureFlags.www.js

@@ -16,6 +16,7 @@ export const {
   debugRenderPhaseSideEffectsForStrictMode,
   disableInputAttributeSyncing,
   enableTrustedTypesIntegration,
+  enableSelectiveHydration,
 } = require('ReactFeatureFlags');
 
 // In www, we have experimental support for gathering data