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
🦋 Changeset detectedLatest commit: 2805eeb The changes in this PR will be included in the next version bump. This PR includes changesets to release 1 package
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Rich-Harris
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Nov 21, 2025
Rich-Harris
approved these changes
Nov 24, 2025
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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