fix(react-router): improve memoization for context providers (#9983)

Co-authored-by: Matt Brophy <matt@brophy.org>

.changeset/popular-timers-sneeze.md

@@ -0,0 +1,5 @@
+---
+"react-router": patch
+---
+
+Improve memoization for context providers to avoid unnecessary re-renders

contributors.yml

@@ -12,6 +12,7 @@
 - AmRo045
 - amsal
 - andreiduca
+- appden
 - arnassavickas
 - aroyan
 - avipatel97

packages/react-router/lib/components.tsx

@@ -56,14 +56,16 @@ export function RouterProvider({
   fallbackElement,
   router,
 }: RouterProviderProps): React.ReactElement {
+  let getState = React.useCallback(() => router.state, [router]);
+
   // Sync router state to our component state to force re-renders
   let state: RouterState = useSyncExternalStoreShim(
     router.subscribe,
-    () => router.state,
+    getState,
     // We have to provide this so React@18 doesn't complain during hydration,
     // but we pass our serialized hydration data into the router so state here
     // is already synced with what the server saw
-    () => router.state
+    getState
   );
 
   let navigator = React.useMemo((): Navigator => {
@@ -87,6 +89,16 @@ export function RouterProvider({
 
   let basename = router.basename || "/";
 
+  let dataRouterContext = React.useMemo(
+    () => ({
+      router,
+      navigator,
+      static: false,
+      basename,
+    }),
+    [router, navigator, basename]
+  );
+
   // The fragment and {null} here are important!  We need them to keep React 18's
   // useId happy when we are server-rendering since we may have a <script> here
   // containing the hydrated server-side staticContext (from StaticRouterProvider).
@@ -95,15 +107,7 @@ export function RouterProvider({
   // we don't need the <script> tag
   return (
     <>
-      <DataRouterContext.Provider
-        value={{
-          router,
-          navigator,
-          static: false,
-          // Do we need this?
-          basename,
-        }}
-      >
+      <DataRouterContext.Provider value={dataRouterContext}>
         <DataRouterStateContext.Provider value={state}>
           <Router
             basename={router.basename}
@@ -330,39 +334,39 @@ export function Router({
     key = "default",
   } = locationProp;
 
-  let location = React.useMemo(() => {
+  let locationContext = React.useMemo(() => {
     let trailingPathname = stripBasename(pathname, basename);
 
     if (trailingPathname == null) {
       return null;
     }
 
     return {
-      pathname: trailingPathname,
-      search,
-      hash,
-      state,
-      key,
+      location: {
+        pathname: trailingPathname,
+        search,
+        hash,
+        state,
+        key,
+      },
+      navigationType,
     };
-  }, [basename, pathname, search, hash, state, key]);
+  }, [basename, pathname, search, hash, state, key, navigationType]);
 
   warning(
-    location != null,
+    locationContext != null,
     `<Router basename="${basename}"> is not able to match the URL ` +
       `"${pathname}${search}${hash}" because it does not start with the ` +
       `basename, so the <Router> won't render anything.`
   );
 
-  if (location == null) {
+  if (locationContext == null) {
     return null;
   }
 
   return (
     <NavigationContext.Provider value={navigationContext}>
-      <LocationContext.Provider
-        children={children}
-        value={{ location, navigationType }}
-      />
+      <LocationContext.Provider children={children} value={locationContext} />
     </NavigationContext.Provider>
   );
 }

packages/react-router/lib/hooks.tsx

@@ -667,6 +667,7 @@ enum DataRouterHook {
 }
 
 enum DataRouterStateHook {
+  UseBlocker = "useBlocker",
   UseLoaderData = "useLoaderData",
   UseActionData = "useActionData",
   UseRouteError = "useRouteError",
@@ -841,6 +842,7 @@ let blockerId = 0;
  */
 export function useBlocker(shouldBlock: boolean | BlockerFunction): Blocker {
   let { router } = useDataRouterContext(DataRouterHook.UseBlocker);
+  let state = useDataRouterState(DataRouterStateHook.UseBlocker);
   let [blockerKey] = React.useState(() => String(++blockerId));
 
   let blockerFunction = React.useCallback<BlockerFunction>(
@@ -860,7 +862,9 @@ export function useBlocker(shouldBlock: boolean | BlockerFunction): Blocker {
     [router, blockerKey]
   );
 
-  return blocker;
+  // Prefer the blocker from state since DataRouterContext is memoized so this
+  // ensures we update on blocker state updates
+  return state.blockers.get(blockerKey) || blocker;
 }
 
 const alreadyWarned: Record<string, boolean> = {};