fix(core): always treat error boundary fallback as a callback

packages/docusaurus-module-type-aliases/src/index.d.ts

@@ -77,14 +77,9 @@ declare module '@theme-original/*';
 declare module '@theme-init/*';
 
 declare module '@theme/Error' {
-  import type {ComponentProps} from 'react';
-  import type ErrorBoundary from '@docusaurus/ErrorBoundary';
+  import type {FallbackParams} from '@docusaurus/ErrorBoundary';
 
-  type ErrorProps = ComponentProps<
-    NonNullable<ComponentProps<typeof ErrorBoundary>['fallback']>
-  >;
-
-  export interface Props extends ErrorProps {}
+  export interface Props extends FallbackParams {}
   export default function Error(props: Props): JSX.Element;
 }
 
@@ -125,13 +120,17 @@ declare module '@docusaurus/constants' {
 }
 
 declare module '@docusaurus/ErrorBoundary' {
-  import type {ReactNode, ComponentType} from 'react';
+  import type {ReactNode} from 'react';
+
+  export type FallbackParams = {
+    readonly error: Error;
+    readonly tryAgain: () => void;
+  };
+
+  export type FallbackFunction = (params: FallbackParams) => JSX.Element;
 
   export interface Props {
-    readonly fallback?: ComponentType<{
-      readonly error: Error;
-      readonly tryAgain: () => void;
-    }>;
+    readonly fallback?: FallbackFunction;
     readonly children: ReactNode;
   }
   export default function ErrorBoundary(props: Props): JSX.Element;

packages/docusaurus-theme-classic/src/theme/Layout/index.tsx

@@ -45,7 +45,9 @@ export default function Layout(props: Props): JSX.Element {
       <Navbar />
 
       <div className={clsx(ThemeClassNames.wrapper.main, wrapperClassName)}>
-        <ErrorBoundary fallback={ErrorPageContent}>{children}</ErrorBoundary>
+        <ErrorBoundary fallback={(params) => <ErrorPageContent {...params} />}>
+          {children}
+        </ErrorBoundary>
       </div>
 
       {!noFooter && <Footer />}

packages/docusaurus/src/client/App.tsx

@@ -23,14 +23,12 @@ import SiteMetadataDefaults from './SiteMetadataDefaults';
 // TODO, quick fix for CSS insertion order
 // eslint-disable-next-line import/order
 import ErrorBoundary from '@docusaurus/ErrorBoundary';
-// eslint-disable-next-line import/order
-import Error from '@theme/Error';
 
 export default function App(): JSX.Element {
   const routeElement = renderRoutes(routes);
   const location = useLocation();
   return (
-    <ErrorBoundary fallback={Error}>
+    <ErrorBoundary>
       <DocusaurusContextProvider>
         <BrowserContextProvider>
           <Root>

packages/docusaurus/src/client/exports/ErrorBoundary.tsx

@@ -7,13 +7,21 @@
 
 import React, {type ReactNode} from 'react';
 import ExecutionEnvironment from '@docusaurus/ExecutionEnvironment';
-import DefaultFallback from '@theme/Error';
-import type {Props} from '@docusaurus/ErrorBoundary';
+import ThemeError from '@theme/Error';
+import type {
+  FallbackFunction,
+  FallbackParams,
+  Props,
+} from '@docusaurus/ErrorBoundary';
 
 type State = {
   error: Error | null;
 };
 
+const DefaultFallback: FallbackFunction = (params) => (
+  <ThemeError {...params} />
+);
+
 export default class ErrorBoundary extends React.Component<Props, State> {
   constructor(props: Props) {
     super(props);
@@ -32,10 +40,12 @@ export default class ErrorBoundary extends React.Component<Props, State> {
     const {error} = this.state;
 
     if (error) {
-      const Fallback = this.props.fallback ?? DefaultFallback;
-      return (
-        <Fallback error={error} tryAgain={() => this.setState({error: null})} />
-      );
+      const fallbackParams: FallbackParams = {
+        error,
+        tryAgain: () => this.setState({error: null}),
+      };
+      const fallback: FallbackFunction = this.props.fallback ?? DefaultFallback;
+      return fallback(fallbackParams);
     }
 
     // See https://github.com/facebook/docusaurus/issues/6337#issuecomment-1012913647

website/docs/docusaurus-core.md

@@ -55,7 +55,13 @@ This component doesn't catch build-time errors and only protects against client-
 
 #### Props {#errorboundary-props}
 
-- `fallback`: a React component. The error boundary will render the component with two props: `error`, the error that was caught, and `tryAgain`, a function (`() => void`) callback to reset the error in the component and try rendering it again.
+- `fallback`: an optional render callback returning a JSX element. It will receive an object with 2 attributes: `error`, the error that was caught, and `tryAgain`, a function (`() => void`) callback to reset the error in the component and try rendering it again. If not present, `@theme/Error` will be rendered instead. `@theme/Error` is used for the error boundaries wrapping the site, above the layout.
+
+:::caution
+
+The `fallback` prop is a callback, and **not a React functional component**. You can't use React hooks inside this callback.
+
+:::
 
 ### `<Head/>` {#head}