fix: flush batches whenever an async value resolves#16912
Merged
Rich-Harris merged 3 commits intomainfrom Oct 8, 2025
Merged
Conversation
🦋 Changeset detectedLatest commit: ec721bb The changes in this PR will be included in the next version bump. This PR includes changesets to release 1 package
Not sure what this means? Click here to learn what changesets are. Click here if you're a maintainer who wants to add another changeset to this PR |
Contributor
|
Member
Author
Merged
dummdidumm
added a commit
that referenced
this pull request
Oct 8, 2025
Test for #16912 Also some explanation what the bug was: 1. async batch kicks off 2. outer async work succeeds, still something pending, so doesn't do anything for now 3. something unrelated writes to a signal (in the remote functions case it's the query writing to loading, raw etc), which creates a new batch 4. new batch executes. since there are multiple batches it takes the previous value which means if block is still alive. commits that, since no async work from the perspective of this branch 5. inner async work succeeds. now the batch has zero pending async work so it can flush. But the if block is no longer dirty since it was done by the other batch already -> never undos the other work #16912 fixes it by still traversing the tree which means the if block deletion is scheduled to commit later, which it then does
dummdidumm
added a commit
that referenced
this pull request
Oct 8, 2025
Test for #16912 Also some explanation what the bug was: 1. async batch kicks off 2. outer async work succeeds, still something pending, so doesn't do anything for now 3. something unrelated writes to a signal (in the remote functions case it's the query writing to loading, raw etc), which creates a new batch 4. new batch executes. since there are multiple batches it takes the previous value which means if block is still alive. commits that, since no async work from the perspective of this branch 5. inner async work succeeds. now the batch has zero pending async work so it can flush. But the if block is no longer dirty since it was done by the other batch already -> never undos the other work #16912 fixes it by still traversing the tree which means the if block deletion is scheduled to commit later, which it then does
This was referenced Oct 13, 2025
Closed
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
1 participant
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 fixes a tricky bug that occurs with remote functions. I struggled to make a narrow repro, but the change is one that makes sense on the face of it: whenever an async value resolves, we update the batch, flushing the change through the effect tree. This has the effect of destroying anything inside blocks that would otherwise keep them alive.
It feels like we might actually need to go even further than this, and deactivate async work inside skipped branches, but I'm not immediately sure how to tackle that, so just making this change for now.
Before submitting the PR, please make sure you do the following
feat:,fix:,chore:, ordocs:.packages/svelte/src, add a changeset (npx changeset).Tests and linting
pnpm testand lint the project withpnpm lint