[Partial Hydration] Render client-only content at normal priority (#15061)

* Split props changing from permanent fallback state

These will need different logic. In this commit, no logic has changed,
only moved.

* Delete terminal fallback content in first pass

If the dehydrated suspense boundary's fallback content is terminal there
is nothing to show. We need to get actual content on the screen soon.

If we deprioritize that work to offscreen, then the timeout heuristics will
be wrong.

Therefore, if we have no current and we're already at terminal fallback
state we'll immediately schedule a deletion and upgrade to real suspense.

* Show failing case when there is another wrapper boundary

* Revert "Delete terminal fallback content in first pass"

This reverts commit ad67ba8.

* Use the new approach of leaving work at normal pri to replace fallback

Author: sebmarkbage

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

@@ -703,6 +703,126 @@ describe('ReactDOMServerPartialHydration', () => {
     expect(ref.current).toBe(span);
   });
 
+  it('replaces the fallback within the maxDuration if there is a nested suspense', async () => {
+    let suspend = false;
+    let promise = new Promise(resolvePromise => {});
+    let ref = React.createRef();
+
+    function Child() {
+      if (suspend) {
+        throw promise;
+      } else {
+        return 'Hello';
+      }
+    }
+
+    function InnerChild() {
+      // Always suspends indefinitely
+      throw promise;
+    }
+
+    function App() {
+      return (
+        <div>
+          <Suspense fallback="Loading..." maxDuration={100}>
+            <span ref={ref}>
+              <Child />
+            </span>
+            <Suspense fallback={null}>
+              <InnerChild />
+            </Suspense>
+          </Suspense>
+        </div>
+      );
+    }
+
+    // First we render the final HTML. With the streaming renderer
+    // this may have suspense points on the server but here we want
+    // to test the completed HTML. Don't suspend on the server.
+    suspend = true;
+    let finalHTML = ReactDOMServer.renderToString(<App />);
+    let container = document.createElement('div');
+    container.innerHTML = finalHTML;
+
+    expect(container.getElementsByTagName('span').length).toBe(0);
+
+    // On the client we have the data available quickly for some reason.
+    suspend = false;
+    let root = ReactDOM.unstable_createRoot(container, {hydrate: true});
+    root.render(<App />);
+    Scheduler.flushAll();
+    // This will have exceeded the maxDuration so we should timeout.
+    jest.advanceTimersByTime(500);
+    // The boundary should longer be suspended for the middle content
+    // even though the inner boundary is still suspended.
+
+    expect(container.textContent).toBe('Hello');
+
+    let span = container.getElementsByTagName('span')[0];
+    expect(ref.current).toBe(span);
+  });
+
+  it('replaces the fallback within the maxDuration if there is a nested suspense in a nested suspense', async () => {
+    let suspend = false;
+    let promise = new Promise(resolvePromise => {});
+    let ref = React.createRef();
+
+    function Child() {
+      if (suspend) {
+        throw promise;
+      } else {
+        return 'Hello';
+      }
+    }
+
+    function InnerChild() {
+      // Always suspends indefinitely
+      throw promise;
+    }
+
+    function App() {
+      return (
+        <div>
+          <Suspense fallback="Another layer">
+            <Suspense fallback="Loading..." maxDuration={100}>
+              <span ref={ref}>
+                <Child />
+              </span>
+              <Suspense fallback={null}>
+                <InnerChild />
+              </Suspense>
+            </Suspense>
+          </Suspense>
+        </div>
+      );
+    }
+
+    // First we render the final HTML. With the streaming renderer
+    // this may have suspense points on the server but here we want
+    // to test the completed HTML. Don't suspend on the server.
+    suspend = true;
+    let finalHTML = ReactDOMServer.renderToString(<App />);
+    let container = document.createElement('div');
+    container.innerHTML = finalHTML;
+
+    expect(container.getElementsByTagName('span').length).toBe(0);
+
+    // On the client we have the data available quickly for some reason.
+    suspend = false;
+    let root = ReactDOM.unstable_createRoot(container, {hydrate: true});
+    root.render(<App />);
+    Scheduler.flushAll();
+    // This will have exceeded the maxDuration so we should timeout.
+    jest.advanceTimersByTime(500);
+    // The boundary should longer be suspended for the middle content
+    // even though the inner boundary is still suspended.
+
+    expect(container.textContent).toBe('Hello');
+
+    let span = container.getElementsByTagName('span')[0];
+    expect(ref.current).toBe(span);
+  });
+
   it('waits for pending content to come in from the server and then hydrates it', async () => {
     let suspend = false;
     let promise = new Promise(resolvePromise => {});

packages/react-reconciler/src/ReactFiberBeginWork.js

@@ -74,7 +74,11 @@ import {
   cloneChildFibers,
 } from './ReactChildFiber';
 import {processUpdateQueue} from './ReactUpdateQueue';
-import {NoWork, Never} from './ReactFiberExpirationTime';
+import {
+  NoWork,
+  Never,
+  computeAsyncExpiration,
+} from './ReactFiberExpirationTime';
 import {
   ConcurrentMode,
   NoContext,
@@ -133,7 +137,7 @@ import {
   createWorkInProgress,
   isSimpleFunctionComponent,
 } from './ReactFiber';
-import {retryTimedOutBoundary} from './ReactFiberScheduler';
+import {requestCurrentTime, retryTimedOutBoundary} from './ReactFiberScheduler';
 
 const ReactCurrentOwner = ReactSharedInternals.ReactCurrentOwner;
 
@@ -1631,15 +1635,71 @@ function updateSuspenseComponent(
   return next;
 }
 
+function retrySuspenseComponentWithoutHydrating(
+  current: Fiber,
+  workInProgress: Fiber,
+  renderExpirationTime: ExpirationTime,
+) {
+  // Detach from the current dehydrated boundary.
+  current.alternate = null;
+  workInProgress.alternate = null;
+
+  // Insert a deletion in the effect list.
+  let returnFiber = workInProgress.return;
+  invariant(
+    returnFiber !== null,
+    'Suspense boundaries are never on the root. ' +
+      'This is probably a bug in React.',
+  );
+  const last = returnFiber.lastEffect;
+  if (last !== null) {
+    last.nextEffect = current;
+    returnFiber.lastEffect = current;
+  } else {
+    returnFiber.firstEffect = returnFiber.lastEffect = current;
+  }
+  current.nextEffect = null;
+  current.effectTag = Deletion;
+
+  // Upgrade this work in progress to a real Suspense component.
+  workInProgress.tag = SuspenseComponent;
+  workInProgress.stateNode = null;
+  workInProgress.memoizedState = null;
+  // This is now an insertion.
+  workInProgress.effectTag |= Placement;
+  // Retry as a real Suspense component.
+  return updateSuspenseComponent(null, workInProgress, renderExpirationTime);
+}
+
 function updateDehydratedSuspenseComponent(
   current: Fiber | null,
   workInProgress: Fiber,
   renderExpirationTime: ExpirationTime,
 ) {
+  const suspenseInstance = (workInProgress.stateNode: SuspenseInstance);
   if (current === null) {
     // During the first pass, we'll bail out and not drill into the children.
     // Instead, we'll leave the content in place and try to hydrate it later.
-    workInProgress.expirationTime = Never;
+    if (isSuspenseInstanceFallback(suspenseInstance)) {
+      // This is a client-only boundary. Since we won't get any content from the server
+      // for this, we need to schedule that at a higher priority based on when it would
+      // have timed out. In theory we could render it in this pass but it would have the
+      // wrong priority associated with it and will prevent hydration of parent path.
+      // Instead, we'll leave work left on it to render it in a separate commit.
+
+      // TODO This time should be the time at which the server rendered response that is
+      // a parent to this boundary was displayed. However, since we currently don't have
+      // a protocol to transfer that time, we'll just estimate it by using the current
+      // time. This will mean that Suspense timeouts are slightly shifted to later than
+      // they should be.
+      let serverDisplayTime = requestCurrentTime();
+      // Schedule a normal pri update to render this content.
+      workInProgress.expirationTime = computeAsyncExpiration(serverDisplayTime);
+    } else {
+      // We'll continue hydrating the rest at offscreen priority since we'll already
+      // be showing the right content coming from the server, it is no rush.
+      workInProgress.expirationTime = Never;
+    }
     return null;
   }
   if ((workInProgress.effectTag & DidCapture) !== NoEffect) {
@@ -1648,55 +1708,31 @@ function updateDehydratedSuspenseComponent(
     workInProgress.child = null;
     return null;
   }
+  if (isSuspenseInstanceFallback(suspenseInstance)) {
+    // This boundary is in a permanent fallback state. In this case, we'll never
+    // get an update and we'll never be able to hydrate the final content. Let's just try the
+    // client side render instead.
+    return retrySuspenseComponentWithoutHydrating(
+      current,
+      workInProgress,
+      renderExpirationTime,
+    );
+  }
   // We use childExpirationTime to indicate that a child might depend on context, so if
   // any context has changed, we need to treat is as if the input might have changed.
   const hasContextChanged = current.childExpirationTime >= renderExpirationTime;
-  const suspenseInstance = (current.stateNode: SuspenseInstance);
-  if (
-    didReceiveUpdate ||
-    hasContextChanged ||
-    isSuspenseInstanceFallback(suspenseInstance)
-  ) {
+  if (didReceiveUpdate || hasContextChanged) {
     // This boundary has changed since the first render. This means that we are now unable to
     // hydrate it. We might still be able to hydrate it using an earlier expiration time but
     // during this render we can't. Instead, we're going to delete the whole subtree and
     // instead inject a new real Suspense boundary to take its place, which may render content
     // or fallback. The real Suspense boundary will suspend for a while so we have some time
     // to ensure it can produce real content, but all state and pending events will be lost.
-
-    // Alternatively, this boundary is in a permanent fallback state. In this case, we'll never
-    // get an update and we'll never be able to hydrate the final content. Let's just try the
-    // client side render instead.
-
-    // Detach from the current dehydrated boundary.
-    current.alternate = null;
-    workInProgress.alternate = null;
-
-    // Insert a deletion in the effect list.
-    let returnFiber = workInProgress.return;
-    invariant(
-      returnFiber !== null,
-      'Suspense boundaries are never on the root. ' +
-        'This is probably a bug in React.',
+    return retrySuspenseComponentWithoutHydrating(
+      current,
+      workInProgress,
+      renderExpirationTime,
     );
-    const last = returnFiber.lastEffect;
-    if (last !== null) {
-      last.nextEffect = current;
-      returnFiber.lastEffect = current;
-    } else {
-      returnFiber.firstEffect = returnFiber.lastEffect = current;
-    }
-    current.nextEffect = null;
-    current.effectTag = Deletion;
-
-    // Upgrade this work in progress to a real Suspense component.
-    workInProgress.tag = SuspenseComponent;
-    workInProgress.stateNode = null;
-    workInProgress.memoizedState = null;
-    // This is now an insertion.
-    workInProgress.effectTag |= Placement;
-    // Retry as a real Suspense component.
-    return updateSuspenseComponent(null, workInProgress, renderExpirationTime);
   } else if (isSuspenseInstancePending(suspenseInstance)) {
     // This component is still pending more data from the server, so we can't hydrate its
     // content. We treat it as if this component suspended itself. It might seem as if