Add todos and proper error message

Author: sammy-SC

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

@@ -727,6 +727,7 @@ export function createFiberFromOffscreen(
     _pendingMarkers: null,
     _retryCache: null,
     _transitions: null,
+    _current: null,
     detach: () => detachOffscreenInstance(primaryChildInstance),
   };
   fiber.stateNode = primaryChildInstance;
@@ -749,6 +750,7 @@ export function createFiberFromLegacyHidden(
     _pendingMarkers: null,
     _transitions: null,
     _retryCache: null,
+    _current: null,
     detach: () => detachOffscreenInstance(instance),
   };
   fiber.stateNode = instance;

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

@@ -683,6 +683,7 @@ function updateOffscreenComponent(
     nextProps.mode === 'hidden' ||
     (enableLegacyHidden &&
       nextProps.mode === 'unstable-defer-without-hiding') ||
+    // TODO: remove read from stateNode.
     workInProgress.stateNode._visibility & OffscreenDetached
   ) {
     // Rendering a hidden tree.

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

@@ -2296,7 +2296,9 @@ function getRetryCache(finishedWork) {
 export function detachOffscreenInstance(instance: OffscreenInstance): void {
   const currentOffscreenFiber = instance._current;
   if (currentOffscreenFiber === null) {
-    throw new Error('TODO: error message');
+    throw new Error(
+      'Calling Offscreen.detach before instance handle has been set.',
+    );
   }
 
   const executionContext = getExecutionContext();
@@ -2697,6 +2699,7 @@ function commitMutationEffectsOnFiber(
       }
 
       commitReconciliationEffects(finishedWork);
+      // TODO: Add explicit effect flag to set _current.
       finishedWork.stateNode._current = finishedWork;
 
       if (flags & Visibility) {

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

@@ -2296,7 +2296,9 @@ function getRetryCache(finishedWork) {
 export function detachOffscreenInstance(instance: OffscreenInstance): void {
   const currentOffscreenFiber = instance._current;
   if (currentOffscreenFiber === null) {
-    throw new Error('TODO: error message');
+    throw new Error(
+      'Calling Offscreen.detach before instance handle has been set.',
+    );
   }
 
   const executionContext = getExecutionContext();

scripts/error-codes/codes.json

@@ -426,5 +426,6 @@
   "438": "An unsupported type was passed to use(): %s",
   "439": "We didn't expect to see a forward reference. This is a bug in the React Server.",
   "440": "A function wrapped in useEvent can't be called during rendering.",
-  "441": "An error occurred in the Server Components render. The specific message is omitted in production builds to avoid leaking sensitive details. A digest property is included on this error instance which may provide additional details about the nature of the error."
+  "441": "An error occurred in the Server Components render. The specific message is omitted in production builds to avoid leaking sensitive details. A digest property is included on this error instance which may provide additional details about the nature of the error.",
+  "442": "Calling Offscreen.detach before instance handle has been set."
 }