[Flight] Fix encodeReply for JSX with temporary references#35730
Merged
unstubbable merged 1 commit intofacebook:mainfrom Feb 9, 2026
Merged
[Flight] Fix encodeReply for JSX with temporary references#35730unstubbable merged 1 commit intofacebook:mainfrom
encodeReply for JSX with temporary references#35730unstubbable merged 1 commit intofacebook:mainfrom
Conversation
`encodeReply` throws "React Element cannot be passed to Server Functions from the Client without a temporary reference set" when a React element is the root value of a `serializeModel` call (either passed directly or resolved from a promise), even when a temporary reference set is provided. The cause is that `resolveToJSON` hits the `REACT_ELEMENT_TYPE` switch case before reaching the `existingReference`/`modelRoot` check that regular objects benefit from. The synthetic JSON root created by `JSON.stringify` is never tracked in `writtenObjects`, so `parentReference` is `undefined` and the code falls through to the throw. This adds a `modelRoot` check in the `REACT_ELEMENT_TYPE` case, following the same pattern used for promises and plain objects. The added `JSX as root model` test also uncovered a pre-existing crash in the Flight Client: when the JSX element round-trips back, it arrives as a frozen object (client-created elements are frozen in DEV), and `Object.defineProperty` for `_debugInfo` fails because frozen objects are non-configurable. The same crash can occur with JSX exported as a client reference. For now, we're adding `!Object.isFrozen()` guards in `moveDebugInfoFromChunkToInnerValue` and `addAsyncInfo` to prevent the crash, which means debug info is silently dropped for frozen elements. The proper fix would likely be to clone the element so each rendering context gets its own mutable copy with correct debug info. closes facebook#34984 closes facebook#35690
github-actions
bot
added
the
React Core Team
|
Comparing: 2dd9b7c...a87af0f Critical size changesIncludes critical production bundles, as well as any change greater than 2%:
Significant size changesIncludes any change greater than 0.2%: Expand to show
|
lubieowoce
reviewed
Feb 9, 2026
| }); | ||
|
|
||
| it('can pass JSX as root model through a round trip using temporary references', async () => { | ||
| const jsx = <div />; |
Contributor
There was a problem hiding this comment.
is this server or client JSX?
Collaborator
Author
There was a problem hiding this comment.
Client, which is the default in our tests, and we use ReactServer.createElement if we want server JSX.
eps1lon
requested changes
Feb 9, 2026
Collaborator
eps1lon
left a comment
eps1lon
left a comment
There was a problem hiding this comment.
Let's discuss a proper fix.
eps1lon
approved these changes
Feb 9, 2026
Collaborator
eps1lon
left a comment
eps1lon
left a comment
There was a problem hiding this comment.
Going with this since there's another bug where debug info is added multiple times for shared elements. No info is better than wrong info.
unstubbable
pushed a commit
to vercel/next.js
that referenced
this pull request
Feb 9, 2026
[diff facebook/react@2dd9b7cf...272441a9](facebook/react@2dd9b7c...272441a) <details> <summary>React upstream changes</summary> - facebook/react#35731 - facebook/react#35730 </details>
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
4 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
encodeReplythrows "React Element cannot be passed to Server Functions from the Client without a temporary reference set" when a React element is the root value of aserializeModelcall (either passed directly or resolved from a promise), even when a temporary reference set is provided.The cause is that
resolveToJSONhits theREACT_ELEMENT_TYPEswitch case before reaching theexistingReference/modelRootcheck that regular objects benefit from. The synthetic JSON root created byJSON.stringifyis never tracked inwrittenObjects, soparentReferenceisundefinedand the code falls through to the throw. This adds amodelRootcheck in theREACT_ELEMENT_TYPEcase, following the same pattern used for promises and plain objects.The added
JSX as root modeltest also uncovered a pre-existing crash in the Flight Client: when the JSX element round-trips back, it arrives as a frozen object (client-created elements are frozen in DEV), andObject.definePropertyfor_debugInfofails because frozen objects are non-configurable. The same crash can occur with JSX exported as a client reference. For now, we're adding!Object.isFrozen()guards inmoveDebugInfoFromChunkToInnerValueandaddAsyncInfoto prevent the crash, which means debug info is silently dropped for frozen elements. The proper fix would likely be to clone the element so each rendering context gets its own mutable copy with correct debug info.closes #34984
closes #35690