fix: reset effects inside skipped branches#17581
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Rich-Harris merged 40 commits intomainfrom Jan 29, 2026
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elliott-with-the-longest-name-on-github
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Jan 28, 2026
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When a branch is speculatively marked for destruction (condition temporarily falsy), its child effects are reset to `CLEAN` to prevent them running in a doomed branch (as of #17581). However, if the branch survives (condition becomes truthy again), those effects remain `CLEAN` and never run - the source was already marked dirty before the reset, so no new dirty marking occurs. The fix is to change `skipped_effects` from a `Set` to a `Map` that tracks which child effects were dirty/maybe_dirty before being reset. When a branch is unskipped (survives), restore their status and reschedule them.
Rich-Harris
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* fix: reschedule effects inside unskipped branches When a branch is speculatively marked for destruction (condition temporarily falsy), its child effects are reset to `CLEAN` to prevent them running in a doomed branch (as of #17581). However, if the branch survives (condition becomes truthy again), those effects remain `CLEAN` and never run - the source was already marked dirty before the reset, so no new dirty marking occurs. The fix is to change `skipped_effects` from a `Set` to a `Map` that tracks which child effects were dirty/maybe_dirty before being reset. When a branch is unskipped (survives), restore their status and reschedule them. * update comment * lint * make skipped_effects private * actually while we're at it let's use a more descriptive name * prettier --------- Co-authored-by: Rich Harris <rich.harris@vercel.com>
dummdidumm
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fixes #17595 When an if/key/etc block has an expression that depends on an async blocker (e.g., is inside a component with top level `await`), the compiler incorrectly treats the expression as async - even when the expression itself contains no `await`. This causes the expression to be added to `$.async`'s `expressions` array, which wraps it in an `async_derived`. This is not only unnecessary but also buggy: it breaks the direct reactive connection between the source and its dependent effects, causing inconsistent effect executions. The fix is to only add expressions to `$.async`'s `expressions` array when they actually contain an `await`. When a branch is speculatively marked for destruction (condition temporarily falsy), its child effects are reset to `CLEAN` to prevent them running in a doomed branch (as of #17581). However, if the branch survives (condition becomes truthy again), those effects remain `CLEAN` and never run - the source was already marked dirty before the reset, so no new dirty marking occurs. The fix is to change `skipped_effects` from a `Set` to a `Map` that tracks which child effects were dirty/maybe_dirty before being reset. When a branch is unskipped (survives), restore their status and reschedule them. --------- Co-authored-by: Rich Harris <rich.harris@vercel.com>
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Alternative to #17335. When traversing, we skip any branches that will be destroyed when the batch commits, so that we don't (for example) try to evaluate
object.propertywhenobjectisundefinedwithin a batch:{#if object} {object.property} {/if}Because of this, however, it's possible for dirty effects inside skipped branches to be left dirty. If they are later rescheduled,
schedule_effectwill bail out if it hits an already-dirty branch, which can prevent state changes from having an effect. This is made more obvious by forks, but doesn't require them.This PR fixes it, by traversing skipped branches when a batch is deferred.
Closes #17197.
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feat:,fix:,chore:, ordocs:.packages/svelte/src, add a changeset (npx changeset).Tests and linting
pnpm testand lint the project withpnpm lint