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chore: warn unnecessary-state-wrap #1272

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hyunbinseo
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@hyunbinseo hyunbinseo commented Jul 17, 2025 •
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There are cases where SvelteSet has to be reassigned. Reference sveltejs/svelte#16422 (comment)

<script lang="ts">
  import { SvelteSet } from 'svelte/reactivity';

  // SvelteSet is already reactive, $state wrapping is unnecessary.
  let ids = $state(new SvelteSet([1]));
  const count = $derived(ids.size); // added
</script>

{#each ids as id (id)}{id}{/each}

<button type="button" onclick={() => (ids = new SvelteSet([2]))}>
  Update IDs
</button>

Since this rule is considered a best practice, the recommendation can be lowered from error to warn.

This will allow devs to comment out the ESLint warning when needed with confidence.

Note

#1202 is a PR for setting ["error", { "allowReassign": true }] as the default option:

https://sveltejs.github.io/eslint-plugin-svelte/rules/no-unnecessary-state-wrap/#allow-reassign

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changeset-bot bot commented Jul 17, 2025

🦋 Changeset detected

Latest commit: b6d3e90

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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eslint-plugin-svelte Patch

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@marekdedic
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Hi,
this is a little bit more complicated issue and I don't think there is a clear agreement :/ For my 2 cents, in your example, the rule pushes you towards using Set.clear(), which is IMO better that re-assignening (at least performance-wise)

@hyunbinseo
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@marekdedic Thanks for the comment.

I am trying to clear and re-add multiple (100+) new items from an array.

Is set.clear() and arr.forEach((v) => set.add(v)) still the advised method?

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@hyunbinseo @marekdedic