Create virtual Fiber when an error occurs during reconcilation

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

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;