perf: store current_sources as Set for O(1) membership checks#18278
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Rich-Harris merged 3 commits intoMay 28, 2026
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The per-reaction collection of "sources created within this reaction" is checked on every signal write inside a reaction (set, dev-mode state_unsafe_mutation guard) and on every self-invalidation scheduling pass. With Array.includes the check was O(n); switching to a Set makes it O(1) and also drops the bound-call indirection of `includes.call`. No semantic change: the collection is still per-reaction, still saved and restored across nested reactions, still seeded by push_reaction_value.
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This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## svelte@5.56.0 ### Minor Changes - feat: allow declarations in the template ([#18282](#18282)) ### Patch Changes - perf: use `createElement` instead of `createElementNS` for HTML elements ([#18262](#18262)) - perf: store `current_sources` as a `Set` for O(1) membership checks ([#18278](#18278)) - perf: deduplicate identical hoisted templates within a component ([#18320](#18320)) - perf: hoist `rest_props` exclude list as a module-scope `Set` ([#18252](#18252)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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current_sourcestracks the sources created within the active reaction so that reading or writing them during that same reaction doesn't trigger a re-run. It was anArraychecked withArray.prototype.includes.call(...)in three hot places: thestate_unsafe_mutationguard,set()'s destruction check, andschedule_possible_effect_self_invalidation.