fix: don't execute attachments and attribute effects eagerly #17208
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attributes_effect and attachments are blocks since they need the managed "don't just destroy children effects"-behavior, but they're not block effects in the sense of "run them eagerly while traversing the effect tree or while flushing effects". Since the latter was the case until now, it meant that forks could cause visible UI updates. This PR introduces a new flag to fix that. `BLOCK_NON_EAGER` is basically a combination of block effects (with respects to the managed behavior) and render effects (with respects to the execution timing). Fixes sveltejs/kit#14931
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Contributor
|
Rich-Harris
reviewed
Nov 21, 2025
| * A block effect that should run as part of render effects, i.e. not eagerly as part of tree traversal or effect flushing. | ||
| * Essentially it is a combination of RENDER_EFFECT and BLOCK_EFFECT. | ||
| */ | ||
| export const BLOCK_NON_EAGER = 1 << 24; |
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BLOCK_NON_EAGER is a bit of a goofy name. I think it would be better if the flags described what effects are rather than what they're not — to me it would make more sense to have a new MANAGED_EFFECT flag that applied to both block effects and managed-but-not-a-block effects. I think that would mean fewer things like the (flags & BLOCK_EFFECT) !== 0 && (flags & BLOCK_NON_EAGER) === 0 check in mark_reactions
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attributes_effect and attachments are blocks since they need the managed "don't just destroy children effects"-behavior, but they're not block effects in the sense of "run them eagerly while traversing the effect tree or while flushing effects". Since the latter was the case until now, it meant that forks could cause visible UI updates.
This PR introduces a new flag to fix that.
BLOCK_NON_EAGERis basically a combination of block effects (with respects to the managed behavior) and render effects (with respects to the execution timing).Fixes sveltejs/kit#14931
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