[Fiber] Use hydration lanes when scheduling hydration work (facebook#31751)

When scheduling the initial root and when using
`unstable_scheduleHydration` we should use the Hydration Lanes rather
than the raw update lane. This ensures that we're always hydrating using
a Hydration Lane or the Offscreen Lane rather than other lanes getting
some random hydration in it.

This fixes an issue where updating a root while it is still hydrating
causes it to trigger client rendering when it could just hydrate and
then apply the update on top of that.

It also fixes a potential performance issue where
`unstable_scheduleHydration` gets batched with an update that then ends
up forcing an update of a boundary that requires it to rewind to do the
hydration lane anyway. Might as well just start with the hydration
without the update applied first.

I added a kill switch (`enableHydrationLaneScheduling`) just in case but
seems very safe given that using `unstable_scheduleHydration` at all is
very rare and updating the root before the shell hydrates is extremely
rare (and used to trigger a recoverable error).

Author: sebmarkbage

packages/react-dom/src/__tests__/ReactDOMFizzShellHydration-test.js

@@ -255,6 +255,39 @@ describe('ReactDOMFizzShellHydration', () => {
     },
   );
 
+  // @gate enableHydrationLaneScheduling
+  it(
+    'updating the root at same priority as initial hydration does not ' +
+      'force a client render',
+    async () => {
+      function App() {
+        return <Text text="Initial" />;
+      }
+
+      // Server render
+      await resolveText('Initial');
+      await serverAct(async () => {
+        const {pipe} = ReactDOMFizzServer.renderToPipeableStream(<App />);
+        pipe(writable);
+      });
+      assertLog(['Initial']);
+
+      await clientAct(async () => {
+        let root;
+        startTransition(() => {
+          root = ReactDOMClient.hydrateRoot(container, <App />);
+        });
+        // This has lower priority than the initial hydration, so the update
+        // won't be processed until after hydration finishes.
+        startTransition(() => {
+          root.render(<Text text="Updated" />);
+        });
+      });
+      assertLog(['Initial', 'Updated']);
+      expect(container.textContent).toBe('Updated');
+    },
+  );
+
   it('updating the root while the shell is suspended forces a client render', async () => {
     function App() {
       return <AsyncText text="Shell" />;

packages/react-reconciler/src/ReactFiberLane.js

@@ -995,61 +995,66 @@ export function getBumpedLaneForHydration(
   renderLanes: Lanes,
 ): Lane {
   const renderLane = getHighestPriorityLane(renderLanes);
-
-  let lane;
-  if ((renderLane & SyncUpdateLanes) !== NoLane) {
-    lane = SyncHydrationLane;
-  } else {
-    switch (renderLane) {
-      case SyncLane:
-        lane = SyncHydrationLane;
-        break;
-      case InputContinuousLane:
-        lane = InputContinuousHydrationLane;
-        break;
-      case DefaultLane:
-        lane = DefaultHydrationLane;
-        break;
-      case TransitionLane1:
-      case TransitionLane2:
-      case TransitionLane3:
-      case TransitionLane4:
-      case TransitionLane5:
-      case TransitionLane6:
-      case TransitionLane7:
-      case TransitionLane8:
-      case TransitionLane9:
-      case TransitionLane10:
-      case TransitionLane11:
-      case TransitionLane12:
-      case TransitionLane13:
-      case TransitionLane14:
-      case TransitionLane15:
-      case RetryLane1:
-      case RetryLane2:
-      case RetryLane3:
-      case RetryLane4:
-        lane = TransitionHydrationLane;
-        break;
-      case IdleLane:
-        lane = IdleHydrationLane;
-        break;
-      default:
-        // Everything else is already either a hydration lane, or shouldn't
-        // be retried at a hydration lane.
-        lane = NoLane;
-        break;
-    }
-  }
-
+  const bumpedLane =
+    (renderLane & SyncUpdateLanes) !== NoLane
+      ? // Unify sync lanes. We don't do this inside getBumpedLaneForHydrationByLane
+        // because that causes things to flush synchronously when they shouldn't.
+        // TODO: This is not coherent but that's beacuse the unification is not coherent.
+        // We need to get merge these into an actual single lane.
+        SyncHydrationLane
+      : getBumpedLaneForHydrationByLane(renderLane);
   // Check if the lane we chose is suspended. If so, that indicates that we
   // already attempted and failed to hydrate at that level. Also check if we're
   // already rendering that lane, which is rare but could happen.
-  if ((lane & (root.suspendedLanes | renderLanes)) !== NoLane) {
+  // TODO: This should move into the caller to decide whether giving up is valid.
+  if ((bumpedLane & (root.suspendedLanes | renderLanes)) !== NoLane) {
     // Give up trying to hydrate and fall back to client render.
     return NoLane;
   }
+  return bumpedLane;
+}
 
+export function getBumpedLaneForHydrationByLane(lane: Lane): Lane {
+  switch (lane) {
+    case SyncLane:
+      lane = SyncHydrationLane;
+      break;
+    case InputContinuousLane:
+      lane = InputContinuousHydrationLane;
+      break;
+    case DefaultLane:
+      lane = DefaultHydrationLane;
+      break;
+    case TransitionLane1:
+    case TransitionLane2:
+    case TransitionLane3:
+    case TransitionLane4:
+    case TransitionLane5:
+    case TransitionLane6:
+    case TransitionLane7:
+    case TransitionLane8:
+    case TransitionLane9:
+    case TransitionLane10:
+    case TransitionLane11:
+    case TransitionLane12:
+    case TransitionLane13:
+    case TransitionLane14:
+    case TransitionLane15:
+    case RetryLane1:
+    case RetryLane2:
+    case RetryLane3:
+    case RetryLane4:
+      lane = TransitionHydrationLane;
+      break;
+    case IdleLane:
+      lane = IdleHydrationLane;
+      break;
+    default:
+      // Everything else is already either a hydration lane, or shouldn't
+      // be retried at a hydration lane.
+      lane = NoLane;
+      break;
+  }
   return lane;
 }
 

packages/react-reconciler/src/ReactFiberReconciler.js

@@ -38,7 +38,10 @@ import {
 } from './ReactWorkTags';
 import getComponentNameFromFiber from 'react-reconciler/src/getComponentNameFromFiber';
 import isArray from 'shared/isArray';
-import {enableSchedulingProfiler} from 'shared/ReactFeatureFlags';
+import {
+  enableSchedulingProfiler,
+  enableHydrationLaneScheduling,
+} from 'shared/ReactFeatureFlags';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import {
   getPublicInstance,
@@ -91,6 +94,7 @@ import {
   SelectiveHydrationLane,
   getHighestPriorityPendingLanes,
   higherPriorityLane,
+  getBumpedLaneForHydrationByLane,
 } from './ReactFiberLane';
 import {
   scheduleRefresh,
@@ -322,7 +326,10 @@ export function createHydrationContainer(
   // the update to schedule work on the root fiber (and, for legacy roots, to
   // enqueue the callback if one is provided).
   const current = root.current;
-  const lane = requestUpdateLane(current);
+  let lane = requestUpdateLane(current);
+  if (enableHydrationLaneScheduling) {
+    lane = getBumpedLaneForHydrationByLane(lane);
+  }
   const update = createUpdate(lane);
   update.callback =
     callback !== undefined && callback !== null ? callback : null;
@@ -533,7 +540,10 @@ export function attemptHydrationAtCurrentPriority(fiber: Fiber): void {
     // their priority other than synchronously flush it.
     return;
   }
-  const lane = requestUpdateLane(fiber);
+  let lane = requestUpdateLane(fiber);
+  if (enableHydrationLaneScheduling) {
+    lane = getBumpedLaneForHydrationByLane(lane);
+  }
   const root = enqueueConcurrentRenderForLane(fiber, lane);
   if (root !== null) {
     scheduleUpdateOnFiber(root, fiber, lane);

packages/shared/ReactFeatureFlags.js

@@ -116,6 +116,8 @@ export const enableSuspenseAvoidThisFallbackFizz = false;
 
 export const enableCPUSuspense = __EXPERIMENTAL__;
 
+export const enableHydrationLaneScheduling = true;
+
 // Enables useMemoCache hook, intended as a compilation target for
 // auto-memoization.
 export const enableUseMemoCacheHook = true;

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

@@ -94,6 +94,7 @@ export const retryLaneExpirationMs = 5000;
 export const syncLaneExpirationMs = 250;
 export const transitionLaneExpirationMs = 5000;
 export const useModernStrictMode = true;
+export const enableHydrationLaneScheduling = true;
 
 // Flow magic to verify the exports of this file match the original version.
 ((((null: any): ExportsType): FeatureFlagsType): ExportsType);

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

@@ -87,6 +87,8 @@ export const useModernStrictMode = true;
 export const enableSiblingPrerendering = true;
 export const enableUseResourceEffectHook = false;
 
+export const enableHydrationLaneScheduling = true;
+
 // Profiling Only
 export const enableProfilerTimer = __PROFILE__;
 export const enableProfilerCommitHooks = __PROFILE__;

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

@@ -49,6 +49,7 @@ export const enableMoveBefore = false;
 export const enableGetInspectorDataForInstanceInProduction = false;
 export const enableFabricCompleteRootInCommitPhase = false;
 export const enableHiddenSubtreeInsertionEffectCleanup = false;
+export const enableHydrationLaneScheduling = true;
 
 export const enableRetryLaneExpiration = false;
 export const retryLaneExpirationMs = 5000;

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

@@ -82,6 +82,7 @@ export const useModernStrictMode = true;
 export const enableFabricCompleteRootInCommitPhase = false;
 export const enableSiblingPrerendering = true;
 export const enableUseResourceEffectHook = true;
+export const enableHydrationLaneScheduling = true;
 
 // Flow magic to verify the exports of this file match the original version.
 ((((null: any): ExportsType): FeatureFlagsType): ExportsType);

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

@@ -97,5 +97,7 @@ export const enableSiblingPrerendering = true;
 
 export const enableUseResourceEffectHook = false;
 
+export const enableHydrationLaneScheduling = true;
+
 // Flow magic to verify the exports of this file match the original version.
 ((((null: any): ExportsType): FeatureFlagsType): ExportsType);

packages/shared/forks/ReactFeatureFlags.www.js

@@ -64,6 +64,8 @@ export const disableInputAttributeSyncing = false;
 export const enableLegacyFBSupport = true;
 export const enableLazyContextPropagation = true;
 
+export const enableHydrationLaneScheduling = true;
+
 export const enableComponentPerformanceTrack = false;
 
 // Logs additional User Timing API marks for use with an experimental profiling tool.