Update error message for suspending at sync priority

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

@@ -187,7 +187,7 @@ describe('ReactDOMServerSuspense', () => {
           1,
         );
       },
-      'Add a <Suspense fallback=...> component higher in the tree',
+      'A component suspended while responding to synchronous input.',
     );
 
     itThrowsWhenRendering(
@@ -200,7 +200,7 @@ describe('ReactDOMServerSuspense', () => {
           1,
         );
       },
-      'Add a <Suspense fallback=...> component higher in the tree',
+      'A component suspended while responding to synchronous input.',
     );
   }
 

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

@@ -78,11 +78,13 @@ function renderToStringImpl(
   }
 
   if (!readyToStream) {
+    // Note: This error message is the one we use on the client. It doesn't
+    // really make sense here. But this is the legacy server renderer, anyway.
+    // We're going to delete it soon.
     throw new Error(
-      'A React component suspended while rendering, but no fallback UI was specified.\n' +
-        '\n' +
-        'Add a <Suspense fallback=...> component higher in the tree to ' +
-        'provide a loading indicator or placeholder to display.',
+      'A component suspended while responding to synchronous input. This ' +
+        'will cause the UI to be replaced with a loading indicator. To fix, ' +
+        'updates that suspend should be wrapped with startTransition.',
     );
   }
 

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

@@ -499,15 +499,11 @@ function throwException(
       // This is a sync/discrete update. We treat this case like an error
       // because discrete renders are expected to produce a complete tree
       // synchronously to maintain consistency with external state.
-
-      // TODO: We should never call getComponentNameFromFiber in production.
-      // Log a warning or something to prevent us from accidentally bundling it.
       const uncaughtSuspenseError = new Error(
-        (getComponentNameFromFiber(sourceFiber) || 'A React component') +
-          ' suspended while rendering, but no fallback UI was specified.\n' +
-          '\n' +
-          'Add a <Suspense fallback=...> component higher in the tree to ' +
-          'provide a loading indicator or placeholder to display.',
+        'A component suspended while responding to synchronous input. This ' +
+          'will cause the UI to be replaced with a loading indicator. To ' +
+          'fix, updates that suspend should be wrapped ' +
+          'with startTransition.',
       );
 
       // If we're outside a transition, fall through to the regular error path.

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

@@ -499,15 +499,11 @@ function throwException(
       // This is a sync/discrete update. We treat this case like an error
       // because discrete renders are expected to produce a complete tree
       // synchronously to maintain consistency with external state.
-
-      // TODO: We should never call getComponentNameFromFiber in production.
-      // Log a warning or something to prevent us from accidentally bundling it.
       const uncaughtSuspenseError = new Error(
-        (getComponentNameFromFiber(sourceFiber) || 'A React component') +
-          ' suspended while rendering, but no fallback UI was specified.\n' +
-          '\n' +
-          'Add a <Suspense fallback=...> component higher in the tree to ' +
-          'provide a loading indicator or placeholder to display.',
+        'A component suspended while responding to synchronous input. This ' +
+          'will cause the UI to be replaced with a loading indicator. To ' +
+          'fix, updates that suspend should be wrapped ' +
+          'with startTransition.',
       );
 
       // If we're outside a transition, fall through to the regular error path.

packages/react-reconciler/src/__tests__/ReactSuspenseWithNoopRenderer-test.js

@@ -1011,9 +1011,7 @@ describe('ReactSuspenseWithNoopRenderer', () => {
       ReactNoop.flushSync(() => {
         ReactNoop.render(<AsyncText text="Async" />);
       });
-    }).toThrow(
-      'AsyncText suspended while rendering, but no fallback UI was specified.',
-    );
+    }).toThrow('A component suspended while responding to synchronous input.');
   });
 
   // @gate enableCache

scripts/error-codes/codes.json

@@ -409,5 +409,6 @@
   "421": "There was an error while hydrating this Suspense boundary. Switched to client rendering.",
   "422": "There was an error while hydrating. Because the error happened outside of a Suspense boundary, the entire root will switch to client rendering.",
   "423": "This root received an early update, before anything was able hydrate. Switched the entire root to client rendering.",
-  "424": "Text content does not match server-rendered HTML."
+  "424": "Text content does not match server-rendered HTML.",
+  "425": "A component suspended while responding to synchronous input. This will cause the UI to be replaced with a loading indicator. To fix, updates that suspend should be wrapped with startTransition."
 }