Change retry priority to "Never" for dehydrated boundaries (#17105)

This changes the "default" retryTime to NoWork which schedules at Normal
pri.

Dehydrated bouundaries normally hydrate at Never priority except when they
retry where we accidentally increased them to Normal because Never was used
as the default value. This changes it so NoWork is the default.

Dehydrated boundaries however get initialized to Never as the default.

Therefore they now hydrate as Never pri unless their priority gets
increased by a forced rerender or selective hydration.

This revealed that erroring at this Never priority can cause an infinite
rerender. So I fixed that too.

Author: sebmarkbage

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

@@ -77,6 +77,7 @@ describe('ReactDOMServerPartialHydration', () => {
     ReactFeatureFlags = require('shared/ReactFeatureFlags');
     ReactFeatureFlags.enableSuspenseCallback = true;
     ReactFeatureFlags.enableFlareAPI = true;
+    ReactFeatureFlags.debugRenderPhaseSideEffectsForStrictMode = false;
 
     React = require('react');
     ReactDOM = require('react-dom');
@@ -2475,4 +2476,85 @@ describe('ReactDOMServerPartialHydration', () => {
 
     document.body.removeChild(container);
   });
+
+  it('finishes normal pri work before continuing to hydrate a retry', async () => {
+    let suspend = false;
+    let resolve;
+    let promise = new Promise(resolvePromise => (resolve = resolvePromise));
+    let ref = React.createRef();
+
+    function Child() {
+      if (suspend) {
+        throw promise;
+      } else {
+        Scheduler.unstable_yieldValue('Child');
+        return 'Hello';
+      }
+    }
+
+    function Sibling() {
+      Scheduler.unstable_yieldValue('Sibling');
+      React.useLayoutEffect(() => {
+        Scheduler.unstable_yieldValue('Commit Sibling');
+      });
+      return 'World';
+    }
+
+    // Avoid rerendering the tree by hoisting it.
+    const tree = (
+      <Suspense fallback="Loading...">
+        <span ref={ref}>
+          <Child />
+        </span>
+      </Suspense>
+    );
+
+    function App({showSibling}) {
+      return (
+        <div>
+          {tree}
+          {showSibling ? <Sibling /> : null}
+        </div>
+      );
+    }
+
+    suspend = false;
+    let finalHTML = ReactDOMServer.renderToString(<App />);
+    expect(Scheduler).toHaveYielded(['Child']);
+
+    let container = document.createElement('div');
+    container.innerHTML = finalHTML;
+
+    suspend = true;
+    let root = ReactDOM.unstable_createRoot(container, {hydrate: true});
+    root.render(<App showSibling={false} />);
+    expect(Scheduler).toFlushAndYield([]);
+
+    expect(ref.current).toBe(null);
+    expect(container.textContent).toBe('Hello');
+
+    // Resolving the promise should continue hydration
+    suspend = false;
+    resolve();
+    await promise;
+
+    Scheduler.unstable_advanceTime(100);
+
+    // Before we have a chance to flush it, we'll also render an update.
+    root.render(<App showSibling={true} />);
+
+    // When we flush we expect the Normal pri render to take priority
+    // over hydration.
+    expect(Scheduler).toFlushAndYieldThrough(['Sibling', 'Commit Sibling']);
+
+    // We shouldn't have hydrated the child yet.
+    expect(ref.current).toBe(null);
+    // But we did have a chance to update the content.
+    expect(container.textContent).toBe('HelloWorld');
+
+    expect(Scheduler).toFlushAndYield(['Child']);
+
+    // Now we're hydrated.
+    expect(ref.current).not.toBe(null);
+  });
 });

packages/react-reconciler/src/ReactFiberBeginWork.js

@@ -1482,7 +1482,7 @@ function validateFunctionComponentInDev(workInProgress: Fiber, Component: any) {
 
 const SUSPENDED_MARKER: SuspenseState = {
   dehydrated: null,
-  retryTime: Never,
+  retryTime: NoWork,
 };
 
 function shouldRemainOnFallback(

packages/react-reconciler/src/ReactFiberSuspenseComponent.js

@@ -35,7 +35,9 @@ export type SuspenseState = {|
   // to check things like isSuspenseInstancePending.
   dehydrated: null | SuspenseInstance,
   // Represents the earliest expiration time we should attempt to hydrate
-  // a dehydrated boundary at. Never is the default.
+  // a dehydrated boundary at.
+  // Never is the default for dehydrated boundaries.
+  // NoWork is the default for normal boundaries, which turns into "normal" pri.
   retryTime: ExpirationTime,
 |};
 

packages/react-reconciler/src/ReactFiberWorkLoop.js

@@ -741,17 +741,19 @@ function finishConcurrentRender(
     // statement, but eslint doesn't know about invariant, so it complains
     // if I do. eslint-disable-next-line no-fallthrough
     case RootErrored: {
-      if (expirationTime !== Idle) {
-        // If this was an async render, the error may have happened due to
-        // a mutation in a concurrent event. Try rendering one more time,
-        // synchronously, to see if the error goes away. If there are
-        // lower priority updates, let's include those, too, in case they
-        // fix the inconsistency. Render at Idle to include all updates.
-        markRootExpiredAtTime(root, Idle);
-        break;
-      }
-      // Commit the root in its errored state.
-      commitRoot(root);
+      // If this was an async render, the error may have happened due to
+      // a mutation in a concurrent event. Try rendering one more time,
+      // synchronously, to see if the error goes away. If there are
+      // lower priority updates, let's include those, too, in case they
+      // fix the inconsistency. Render at Idle to include all updates.
+      // If it was Idle or Never or some not-yet-invented time, render
+      // at that time.
+      markRootExpiredAtTime(
+        root,
+        expirationTime > Idle ? Idle : expirationTime,
+      );
+      // We assume that this second render pass will be synchronous
+      // and therefore not hit this path again.
       break;
     }
     case RootSuspended: {
@@ -2376,7 +2378,7 @@ function retryTimedOutBoundary(
   // previously was rendered in its fallback state. One of the promises that
   // suspended it has resolved, which means at least part of the tree was
   // likely unblocked. Try rendering again, at a new expiration time.
-  if (retryTime === Never) {
+  if (retryTime === NoWork) {
     const suspenseConfig = null; // Retries don't carry over the already committed update.
     const currentTime = requestCurrentTime();
     retryTime = computeExpirationForFiber(
@@ -2395,15 +2397,15 @@ function retryTimedOutBoundary(
 
 export function retryDehydratedSuspenseBoundary(boundaryFiber: Fiber) {
   const suspenseState: null | SuspenseState = boundaryFiber.memoizedState;
-  let retryTime = Never;
+  let retryTime = NoWork;
   if (suspenseState !== null) {
     retryTime = suspenseState.retryTime;
   }
   retryTimedOutBoundary(boundaryFiber, retryTime);
 }
 
 export function resolveRetryThenable(boundaryFiber: Fiber, thenable: Thenable) {
-  let retryTime = Never; // Default
+  let retryTime = NoWork; // Default
   let retryCache: WeakSet<Thenable> | Set<Thenable> | null;
   if (enableSuspenseServerRenderer) {
     switch (boundaryFiber.tag) {