Uh oh!
There was an error while loading. Please reload this page.
[Fiber] getNearestMountedFiber should consider fibers with alternates as mounted - #35578
Merged
Conversation
sebmarkbageforce-pushed
the
fixismounted
branch
2 times, most recently
from
January 21, 2026 03:26
3bd4875 to
2ca7f48Comparesebmarkbageforce-pushed
the
fixismounted
branch
from
January 21, 2026 03:29
2ca7f48 to
e0b2e86Compareacdlite
approved these changes
Jan 21, 2026
Uh oh!
There was an error while loading. Please reload this page.
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 freeto join this conversation on GitHub.
Already have an account?
Sign in to comment
3 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Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be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.
This is a 10 year old bug which can cause events to get dropped and other things.
To know if an instance is mounted (or which nearest instance is mounted) we can normally back track and see if a
.returnpointer goes all the way to the root or if it'snullbefore that (which indicates a disconnected tree).One exception to that is if we're looking at a new tree that has not been mounted yet. Its return pointers will point to the parents that rendered it. To detect this we check new tree if they have a Placement flag. If they do then we haven't yet mounted that tree and so it's considered not mounted.
However, the Placement flag is also used for reorders. It's only an insertion if it's on a fiber with no alternates. This algorithm didn't consider that the target might be have no alternates but a parent has alternates. Those same parents may be reordered. So if you reordered a parent without rerendering the child. The child could stop receiving events. This mainly is an issue if the rerender didn't commit. E.g. was suspended (or in this case was a gesture) which is likely why it infrequently would be observable and very hard to repro.
This fixes that by bailing when we find an alternate and then proceeding to check if that tree is still connected.
Needs tests.