Capture suspense boundaries with undefined fallbacks

Author: rickhanlonii

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

@@ -714,7 +714,7 @@ describe('ReactDOMServerPartialHydration', () => {
     expect(container.textContent).toBe('Hi');
   });
 
-  it('shows the fallback of the outer if fallback is missing', async () => {
+  it('treats missing fallback the same as if it was defined', async () => {
     // This is the same exact test as above but with a nested Suspense without a fallback.
     // This should be a noop.
     let suspend = false;
@@ -759,7 +759,8 @@ describe('ReactDOMServerPartialHydration', () => {
     Scheduler.unstable_flushAll();
     jest.runAllTimers();
 
-    expect(ref.current).toBe(null);
+    const span = container.getElementsByTagName('span')[0];
+    expect(ref.current).toBe(span);
 
     // Render an update, but leave it still suspended.
     root.render(<App text="Hi" className="hi" />);
@@ -768,9 +769,9 @@ describe('ReactDOMServerPartialHydration', () => {
     Scheduler.unstable_flushAll();
     jest.runAllTimers();
 
-    expect(container.getElementsByTagName('span').length).toBe(0);
-    expect(ref.current).toBe(null);
-    expect(container.textContent).toBe('Loading...');
+    expect(container.getElementsByTagName('span').length).toBe(1);
+    expect(ref.current).toBe(span);
+    expect(container.textContent).toBe('');
 
     // Unsuspending shows the content.
     suspend = false;
@@ -780,7 +781,6 @@ describe('ReactDOMServerPartialHydration', () => {
     Scheduler.unstable_flushAll();
     jest.runAllTimers();
 
-    const span = container.getElementsByTagName('span')[0];
     expect(span.textContent).toBe('Hi');
     expect(span.className).toBe('hi');
     expect(ref.current).toBe(span);

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

@@ -471,10 +471,12 @@ describe('ReactDOMServerHydration', () => {
       element,
     );
 
-    // Because this didn't have a fallback, it was hydrated as if it's
-    // not a Suspense boundary.
-    expect(ref.current).toBe(div);
-    expect(element.innerHTML).toBe('<div>Hello World</div>');
+    // The content should've been client rendered.
+    expect(ref.current).not.toBe(div);
+    // Unfortunately, since we don't delete the tail at the root, a duplicate will remain.
+    expect(element.innerHTML).toBe(
+      '<div>Hello World</div><div>Hello World</div>',
+    );
   });
 
   // regression test for https://github.com/facebook/react/issues/17170

packages/react-dom/src/server/ReactPartialRenderer.js

@@ -1123,25 +1123,6 @@ class ReactDOMServerRenderer {
         case REACT_SUSPENSE_TYPE: {
           if (enableSuspenseServerRenderer) {
             const fallback = ((nextChild: any): ReactElement).props.fallback;
-            if (fallback === undefined) {
-              // If there is no fallback, then this just behaves as a fragment.
-              const nextChildren = toArray(
-                ((nextChild: any): ReactElement).props.children,
-              );
-              const frame: Frame = {
-                type: null,
-                domNamespace: parentNamespace,
-                children: nextChildren,
-                childIndex: 0,
-                context: context,
-                footer: '',
-              };
-              if (__DEV__) {
-                ((frame: any): FrameDev).debugElementStack = [];
-              }
-              this.stack.push(frame);
-              return '';
-            }
             const fallbackChildren = toArray(fallback);
             const nextChildren = toArray(
               ((nextChild: any): ReactElement).props.children,

packages/react-reconciler/src/ReactFiberBeginWork.new.js

@@ -1867,12 +1867,8 @@ function updateSuspenseComponent(current, workInProgress, renderLanes) {
       // This is a new mount or this boundary is already showing a fallback state.
       // Mark this subtree context as having at least one invisible parent that could
       // handle the fallback state.
-      // Boundaries without fallbacks or should be avoided are not considered since
-      // they cannot handle preferred fallback states.
-      if (
-        nextProps.fallback !== undefined &&
-        nextProps.unstable_avoidThisFallback !== true
-      ) {
+      // Avoided boundaries are not considered since they cannot handle preferred fallback states.
+      if (nextProps.unstable_avoidThisFallback !== true) {
         suspenseContext = addSubtreeSuspenseContext(
           suspenseContext,
           InvisibleParentSuspenseContext,
@@ -1910,22 +1906,18 @@ function updateSuspenseComponent(current, workInProgress, renderLanes) {
   if (current === null) {
     // Initial mount
     // If we're currently hydrating, try to hydrate this boundary.
-    // But only if this has a fallback.
-    if (nextProps.fallback !== undefined) {
-      tryToClaimNextHydratableInstance(workInProgress);
-      // This could've been a dehydrated suspense component.
-      if (enableSuspenseServerRenderer) {
-        const suspenseState: null | SuspenseState =
-          workInProgress.memoizedState;
-        if (suspenseState !== null) {
-          const dehydrated = suspenseState.dehydrated;
-          if (dehydrated !== null) {
-            return mountDehydratedSuspenseComponent(
-              workInProgress,
-              dehydrated,
-              renderLanes,
-            );
-          }
+    tryToClaimNextHydratableInstance(workInProgress);
+    // This could've been a dehydrated suspense component.
+    if (enableSuspenseServerRenderer) {
+      const suspenseState: null | SuspenseState = workInProgress.memoizedState;
+      if (suspenseState !== null) {
+        const dehydrated = suspenseState.dehydrated;
+        if (dehydrated !== null) {
+          return mountDehydratedSuspenseComponent(
+            workInProgress,
+            dehydrated,
+            renderLanes,
+          );
         }
       }
     }

packages/react-reconciler/src/ReactFiberBeginWork.old.js

@@ -1867,12 +1867,8 @@ function updateSuspenseComponent(current, workInProgress, renderLanes) {
       // This is a new mount or this boundary is already showing a fallback state.
       // Mark this subtree context as having at least one invisible parent that could
       // handle the fallback state.
-      // Boundaries without fallbacks or should be avoided are not considered since
-      // they cannot handle preferred fallback states.
-      if (
-        nextProps.fallback !== undefined &&
-        nextProps.unstable_avoidThisFallback !== true
-      ) {
+      // Avoided boundaries are not considered since they cannot handle preferred fallback states.
+      if (nextProps.unstable_avoidThisFallback !== true) {
         suspenseContext = addSubtreeSuspenseContext(
           suspenseContext,
           InvisibleParentSuspenseContext,
@@ -1910,22 +1906,18 @@ function updateSuspenseComponent(current, workInProgress, renderLanes) {
   if (current === null) {
     // Initial mount
     // If we're currently hydrating, try to hydrate this boundary.
-    // But only if this has a fallback.
-    if (nextProps.fallback !== undefined) {
-      tryToClaimNextHydratableInstance(workInProgress);
-      // This could've been a dehydrated suspense component.
-      if (enableSuspenseServerRenderer) {
-        const suspenseState: null | SuspenseState =
-          workInProgress.memoizedState;
-        if (suspenseState !== null) {
-          const dehydrated = suspenseState.dehydrated;
-          if (dehydrated !== null) {
-            return mountDehydratedSuspenseComponent(
-              workInProgress,
-              dehydrated,
-              renderLanes,
-            );
-          }
+    tryToClaimNextHydratableInstance(workInProgress);
+    // This could've been a dehydrated suspense component.
+    if (enableSuspenseServerRenderer) {
+      const suspenseState: null | SuspenseState = workInProgress.memoizedState;
+      if (suspenseState !== null) {
+        const dehydrated = suspenseState.dehydrated;
+        if (dehydrated !== null) {
+          return mountDehydratedSuspenseComponent(
+            workInProgress,
+            dehydrated,
+            renderLanes,
+          );
         }
       }
     }

packages/react-reconciler/src/ReactFiberCompleteWork.new.js

@@ -1045,9 +1045,7 @@ function completeWork(
       const nextDidTimeout = nextState !== null;
       let prevDidTimeout = false;
       if (current === null) {
-        if (workInProgress.memoizedProps.fallback !== undefined) {
-          popHydrationState(workInProgress);
-        }
+        popHydrationState(workInProgress);
       } else {
         const prevState: null | SuspenseState = current.memoizedState;
         prevDidTimeout = prevState !== null;

packages/react-reconciler/src/ReactFiberCompleteWork.old.js

@@ -1045,9 +1045,7 @@ function completeWork(
       const nextDidTimeout = nextState !== null;
       let prevDidTimeout = false;
       if (current === null) {
-        if (workInProgress.memoizedProps.fallback !== undefined) {
-          popHydrationState(workInProgress);
-        }
+        popHydrationState(workInProgress);
       } else {
         const prevState: null | SuspenseState = current.memoizedState;
         prevDidTimeout = prevState !== null;

packages/react-reconciler/src/ReactFiberSuspenseComponent.new.js

@@ -77,10 +77,6 @@ export function shouldCaptureSuspense(
     return false;
   }
   const props = workInProgress.memoizedProps;
-  // In order to capture, the Suspense component must have a fallback prop.
-  if (props.fallback === undefined) {
-    return false;
-  }
   // Regular boundaries always capture.
   if (props.unstable_avoidThisFallback !== true) {
     return true;

packages/react-reconciler/src/ReactFiberSuspenseComponent.old.js

@@ -77,10 +77,6 @@ export function shouldCaptureSuspense(
     return false;
   }
   const props = workInProgress.memoizedProps;
-  // In order to capture, the Suspense component must have a fallback prop.
-  if (props.fallback === undefined) {
-    return false;
-  }
   // Regular boundaries always capture.
   if (props.unstable_avoidThisFallback !== true) {
     return true;

packages/react-reconciler/src/__tests__/ReactHooks-test.internal.js

@@ -19,8 +19,6 @@ let Scheduler;
 let ReactDOMServer;
 let act;
 
-// Additional tests can be found in ReactHooksWithNoopRenderer. Plan is to
-// gradually migrate those to this file.
 describe('ReactHooks', () => {
   beforeEach(() => {
     jest.resetModules();