[Fiber] Create virtual Fiber when an error occurs during reconcilation (#29804)

This lets us rethrow it in the conceptual place of the child.

There's currently a problem when we suspend or throw in the child fiber
reconciliation phase. This work is done by the parent component, so if
it suspends or errors it is as if that component errored or suspended.
However, conceptually it's like a child suspended or errored.

In theory any thing can throw but it is really mainly due to either
`React.lazy` (both in the element.type position and node position),
`Thenable`s or the `Thenable`s that make up `AsyncIterable`s.

Mainly this happens because a Server Component that errors turns into a
`React.lazy`. In practice this means that if you have a Server Component
as the direct child of an Error Boundary. Errors inside of it won't be
caught.

We used to have the same problem with Thenables and Suspense but because
it's now always nested inside an inner Offscreen boundary that shields
it by being one level nested. However, when we have raw Offscreen
(Activity) boundaries they should also be able to catch the suspense if
it's in a hidden state so the problem returns. This fixes it for thrown
promises but it doesn't fix it for SuspenseException. I'm not sure this
is even the right strategy for Suspense though. It kind of relies on the
node never actually mounting/committing.

It's conceptually a little tricky because the current component can
inspect the children and make decisions based on them. Such as
SuspenseList.

The other thing that this PR tries to address is that it sets the
foundation for dealing with error reporting for Server Components that
errored. If something client side errors it'll be a stack like Server
(DebugInfo) -> Fiber -> Fiber -> Server -> (DebugInfo) -> Fiber.
However, all error reporting relies on it eventually terminating into a
Fiber that is responsible for the error. To avoid having to fork too
much it would be nice if I could create a Fiber to associate with the
error so that even a Server component error in this case ultimately
terminates in a Fiber.

packages/react-client/src/__tests__/ReactFlight-test.js

@@ -964,67 +964,47 @@ describe('ReactFlight', () => {
     const testCases = (
       <>
         <ClientErrorBoundary expectedMessage="This is a real Error.">
-          <div>
-            <Throw value={new TypeError('This is a real Error.')} />
-          </div>
+          <Throw value={new TypeError('This is a real Error.')} />
         </ClientErrorBoundary>
         <ClientErrorBoundary expectedMessage="This is a string error.">
-          <div>
-            <Throw value="This is a string error." />
-          </div>
+          <Throw value="This is a string error." />
         </ClientErrorBoundary>
         <ClientErrorBoundary expectedMessage="{message: ..., extra: ..., nested: ...}">
-          <div>
-            <Throw
-              value={{
-                message: 'This is a long message',
-                extra: 'properties',
-                nested: {more: 'prop'},
-              }}
-            />
-          </div>
+          <Throw
+            value={{
+              message: 'This is a long message',
+              extra: 'properties',
+              nested: {more: 'prop'},
+            }}
+          />
         </ClientErrorBoundary>
         <ClientErrorBoundary
           expectedMessage={'{message: "Short", extra: ..., nested: ...}'}>
-          <div>
-            <Throw
-              value={{
-                message: 'Short',
-                extra: 'properties',
-                nested: {more: 'prop'},
-              }}
-            />
-          </div>
+          <Throw
+            value={{
+              message: 'Short',
+              extra: 'properties',
+              nested: {more: 'prop'},
+            }}
+          />
         </ClientErrorBoundary>
         <ClientErrorBoundary expectedMessage="Symbol(hello)">
-          <div>
-            <Throw value={Symbol('hello')} />
-          </div>
+          <Throw value={Symbol('hello')} />
         </ClientErrorBoundary>
         <ClientErrorBoundary expectedMessage="123">
-          <div>
-            <Throw value={123} />
-          </div>
+          <Throw value={123} />
         </ClientErrorBoundary>
         <ClientErrorBoundary expectedMessage="undefined">
-          <div>
-            <Throw value={undefined} />
-          </div>
+          <Throw value={undefined} />
         </ClientErrorBoundary>
         <ClientErrorBoundary expectedMessage="<div/>">
-          <div>
-            <Throw value={<div />} />
-          </div>
+          <Throw value={<div />} />
         </ClientErrorBoundary>
         <ClientErrorBoundary expectedMessage="function Foo() {}">
-          <div>
-            <Throw value={function Foo() {}} />
-          </div>
+          <Throw value={function Foo() {}} />
         </ClientErrorBoundary>
         <ClientErrorBoundary expectedMessage={'["array"]'}>
-          <div>
-            <Throw value={['array']} />
-          </div>
+          <Throw value={['array']} />
         </ClientErrorBoundary>
         <ClientErrorBoundary
           expectedMessage={
@@ -1034,9 +1014,7 @@ describe('ReactFlight', () => {
             '- A library pre-bundled an old copy of "react" or "react/jsx-runtime".\n' +
             '- A compiler tries to "inline" JSX instead of using the runtime.'
           }>
-          <div>
-            <LazyInlined />
-          </div>
+          <LazyInlined />
         </ClientErrorBoundary>
       </>
     );

packages/react-devtools-shared/src/backend/renderer.js

@@ -268,6 +268,7 @@ export function getInternalReactConstants(version: string): {
       TracingMarkerComponent: 25, // Experimental - This is technically in 18 but we don't
       // want to fork again so we're adding it here instead
       YieldComponent: -1, // Removed
+      Throw: 29,
     };
   } else if (gte(version, '17.0.0-alpha')) {
     ReactTypeOfWork = {
@@ -302,6 +303,7 @@ export function getInternalReactConstants(version: string): {
       SuspenseListComponent: 19, // Experimental
       TracingMarkerComponent: -1, // Doesn't exist yet
       YieldComponent: -1, // Removed
+      Throw: -1, // Doesn't exist yet
     };
   } else if (gte(version, '16.6.0-beta.0')) {
     ReactTypeOfWork = {
@@ -336,6 +338,7 @@ export function getInternalReactConstants(version: string): {
       SuspenseListComponent: 19, // Experimental
       TracingMarkerComponent: -1, // Doesn't exist yet
       YieldComponent: -1, // Removed
+      Throw: -1, // Doesn't exist yet
     };
   } else if (gte(version, '16.4.3-alpha')) {
     ReactTypeOfWork = {
@@ -370,6 +373,7 @@ export function getInternalReactConstants(version: string): {
       SuspenseListComponent: -1, // Doesn't exist yet
       TracingMarkerComponent: -1, // Doesn't exist yet
       YieldComponent: -1, // Removed
+      Throw: -1, // Doesn't exist yet
     };
   } else {
     ReactTypeOfWork = {
@@ -404,6 +408,7 @@ export function getInternalReactConstants(version: string): {
       SuspenseListComponent: -1, // Doesn't exist yet
       TracingMarkerComponent: -1, // Doesn't exist yet
       YieldComponent: 9,
+      Throw: -1, // Doesn't exist yet
     };
   }
   // **********************************************************
@@ -445,6 +450,7 @@ export function getInternalReactConstants(version: string): {
     SuspenseComponent,
     SuspenseListComponent,
     TracingMarkerComponent,
+    Throw,
   } = ReactTypeOfWork;
 
   function resolveFiberType(type: any): $FlowFixMe {
@@ -551,6 +557,9 @@ export function getInternalReactConstants(version: string): {
         return 'Profiler';
       case TracingMarkerComponent:
         return 'TracingMarker';
+      case Throw:
+        // This should really never be visible.
+        return 'Error';
       default:
         const typeSymbol = getTypeSymbol(type);
 
@@ -672,6 +681,7 @@ export function attach(
     SuspenseComponent,
     SuspenseListComponent,
     TracingMarkerComponent,
+    Throw,
   } = ReactTypeOfWork;
   const {
     ImmediatePriority,
@@ -1036,6 +1046,7 @@ export function attach(
       case HostText:
       case LegacyHiddenComponent:
       case OffscreenComponent:
+      case Throw:
         return true;
       case HostRoot:
         // It is never valid to filter the root element.

packages/react-devtools-shared/src/backend/types.js

@@ -72,6 +72,7 @@ export type WorkTagMap = {
   SuspenseListComponent: WorkTag,
   TracingMarkerComponent: WorkTag,
   YieldComponent: WorkTag,
+  Throw: WorkTag,
 };
 
 // TODO: If it's useful for the frontend to know which types of data an Element has

packages/react-reconciler/src/ReactChildFiber.js

@@ -25,6 +25,7 @@ import {
   Forked,
   PlacementDEV,
 } from './ReactFiberFlags';
+import {NoMode, ConcurrentMode} from './ReactTypeOfMode';
 import {
   getIteratorFn,
   ASYNC_ITERATOR,
@@ -46,6 +47,7 @@ import isArray from 'shared/isArray';
 import {
   enableRefAsProp,
   enableAsyncIterableChildren,
+  disableLegacyMode,
 } from 'shared/ReactFeatureFlags';
 
 import {
@@ -55,11 +57,16 @@ import {
   createFiberFromFragment,
   createFiberFromText,
   createFiberFromPortal,
+  createFiberFromThrow,
 } from './ReactFiber';
 import {isCompatibleFamilyForHotReloading} from './ReactFiberHotReloading';
 import {getIsHydrating} from './ReactFiberHydrationContext';
 import {pushTreeFork} from './ReactFiberTreeContext';
-import {createThenableState, trackUsedThenable} from './ReactFiberThenable';
+import {
+  SuspenseException,
+  createThenableState,
+  trackUsedThenable,
+} from './ReactFiberThenable';
 import {readContextDuringReconciliation} from './ReactFiberNewContext';
 import {callLazyInitInDEV} from './ReactFiberCallUserSpace';
 
@@ -1919,20 +1926,45 @@ function createChildReconciler(
     newChild: any,
     lanes: Lanes,
   ): Fiber | null {
-    // This indirection only exists so we can reset `thenableState` at the end.
-    // It should get inlined by Closure.
-    thenableIndexCounter = 0;
-    const firstChildFiber = reconcileChildFibersImpl(
-      returnFiber,
-      currentFirstChild,
-      newChild,
-      lanes,
-      null, // debugInfo
-    );
-    thenableState = null;
-    // Don't bother to reset `thenableIndexCounter` to 0 because it always gets
-    // set at the beginning.
-    return firstChildFiber;
+    try {
+      // This indirection only exists so we can reset `thenableState` at the end.
+      // It should get inlined by Closure.
+      thenableIndexCounter = 0;
+      const firstChildFiber = reconcileChildFibersImpl(
+        returnFiber,
+        currentFirstChild,
+        newChild,
+        lanes,
+        null, // debugInfo
+      );
+      thenableState = null;
+      // Don't bother to reset `thenableIndexCounter` to 0 because it always gets
+      // set at the beginning.
+      return firstChildFiber;
+    } catch (x) {
+      if (
+        x === SuspenseException ||
+        (!disableLegacyMode &&
+          (returnFiber.mode & ConcurrentMode) === NoMode &&
+          typeof x === 'object' &&
+          x !== null &&
+          typeof x.then === 'function')
+      ) {
+        // Suspense exceptions need to read the current suspended state before
+        // yielding and replay it using the same sequence so this trick doesn't
+        // work here.
+        // Suspending in legacy mode actually mounts so if we let the child
+        // mount then we delete its state in an update.
+        throw x;
+      }
+      // Something errored during reconciliation but it's conceptually a child that
+      // errored and not the current component itself so we create a virtual child
+      // that throws in its begin phase. That way the current component can handle
+      // the error or suspending if needed.
+      const throwFiber = createFiberFromThrow(x, returnFiber.mode, lanes);
+      throwFiber.return = returnFiber;
+      return throwFiber;
+    }
   }
 
   return reconcileChildFibers;

packages/react-reconciler/src/ReactFiber.js

@@ -67,6 +67,7 @@ import {
   OffscreenComponent,
   LegacyHiddenComponent,
   TracingMarkerComponent,
+  Throw,
 } from './ReactWorkTags';
 import {OffscreenVisible} from './ReactFiberActivityComponent';
 import {getComponentNameFromOwner} from 'react-reconciler/src/getComponentNameFromFiber';
@@ -879,3 +880,13 @@ export function createFiberFromPortal(
   };
   return fiber;
 }
+
+export function createFiberFromThrow(
+  error: mixed,
+  mode: TypeOfMode,
+  lanes: Lanes,
+): Fiber {
+  const fiber = createFiber(Throw, error, null, mode);
+  fiber.lanes = lanes;
+  return fiber;
+}

packages/react-reconciler/src/ReactFiberBeginWork.js

@@ -72,6 +72,7 @@ import {
   LegacyHiddenComponent,
   CacheComponent,
   TracingMarkerComponent,
+  Throw,
 } from './ReactWorkTags';
 import {
   NoFlags,
@@ -4126,6 +4127,11 @@ function beginWork(
       }
       break;
     }
+    case Throw: {
+      // This represents a Component that threw in the reconciliation phase.
+      // So we'll rethrow here. This might be
+      throw workInProgress.pendingProps;
+    }
   }
 
   throw new Error(

packages/react-reconciler/src/ReactFiberCompleteWork.js

@@ -72,6 +72,7 @@ import {
   LegacyHiddenComponent,
   CacheComponent,
   TracingMarkerComponent,
+  Throw,
 } from './ReactWorkTags';
 import {NoMode, ConcurrentMode, ProfileMode} from './ReactTypeOfMode';
 import {
@@ -1802,6 +1803,12 @@ function completeWork(
       }
       return null;
     }
+    case Throw: {
+      if (!disableLegacyMode) {
+        // Only Legacy Mode completes an errored node.
+        return null;
+      }
+    }
   }
 
   throw new Error(

packages/react-reconciler/src/ReactWorkTags.js

@@ -36,7 +36,8 @@ export type WorkTag =
   | 25
   | 26
   | 27
-  | 28;
+  | 28
+  | 29;
 
 export const FunctionComponent = 0;
 export const ClassComponent = 1;
@@ -65,3 +66,4 @@ export const TracingMarkerComponent = 25;
 export const HostHoistable = 26;
 export const HostSingleton = 27;
 export const IncompleteFunctionComponent = 28;
+export const Throw = 29;