fix: parse declaration tags with a division operator in the initializer by hjaber · Pull Request #18353 · sveltejs/svelte

hjaber · 2026-06-01T18:23:58Z

{const ratio = width / height}, or any declaration tag with a top-level / in its initializer, currently fails to compile with unexpected_eof.

parse_statement_at figures out where the statement ends with find_matching_bracket, and that scanner treats every / as the start of a regex literal, so it skips past the real } and runs to the next unrelated / or EOF. {@const} isn't affected because it reads its initializer through acorn's parseExpressionAt, which knows a / after a value is division.

This parses the declaration with acorn directly instead, so acorn decides regex-vs-division (and handles comments, keywords, TS annotations, destructuring and multi-declarator declarations) and reports the real statement end. find_matching_bracket is unchanged and still used by the loose-parsing paths.

Added a print test sample (declaration-tag-division) covering top-level division, $derived(a / b), member/call/string operands, a TS type annotation and a destructuring default, plus a regex containing } (/[}]/). On main the division cases throw unexpected_eof; with the fix the sample parses and round-trips. The regex case matters: a regex containing } is exactly what a weaker fix would misread as the tag close.

changeset-bot · 2026-06-01T18:24:03Z

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Latest commit: d8e126d

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vercel

Additional Suggestion:

Test expects unexpected_eof error but the new acorn-based implementation produces js_parse_error instead.

parse_statement_at now drives the boundary with acorn, so an unterminated declaration tag (e.g. `{let x = a /`) surfaced acorn's generic js_parse_error instead of the unexpected_eof diagnostic the declaration-tag-trailing-slash test (sveltejs#18350) relies on. Remap acorn's end-of-input error (err.pos at the end of the source) back to unexpected_eof; other malformed-at-EOF inputs keep their more specific acorn message. Also cast the parsed Statement to acorn.Node for add_comments, resolving the TS2345 from estree Statement.start being number|undefined.

hjaber · 2026-06-01T18:58:15Z

Both review-bot findings were correct. Pushed ad576ed to address them.

1. unexpected_eof -> js_parse_error (api-compatibility). Right that the pre-existing declaration-tag-trailing-slash test ({let x = a /, added in #18350) regressed, since parse_statement_at no longer produces unexpected_eof. Rather than downgrade that test's expectation, I preserved #18350's contract: when acorn's error lands at the end of the source (err.pos === source.length, i.e. it genuinely ran out of input), it's remapped back to unexpected_eof. This is more precise than the old find_matching_bracket behaviour, which mapped every unterminated tag to unexpected_eof:

{let x = a / -> unexpected_eof "Unexpected end of input" [12,12] (test passes unchanged)
{let x = a /} -> js_parse_error at the } (brace present, not EOF, correctly not remapped)
{const s = "abc -> keeps acorn's specific "Unterminated string constant"

(One thing I also corrected: the catch variable was named e, which shadowed the imported errors module e, so e.unexpected_eof would not have resolved to the error helper. Renamed to err.)

2. TS2345 on add_comments (type-safety). Correct, the new code introduced it (estree Statement.start is number | undefined vs acorn's Node.start: number). Applied the suggested cast to acorn.Node.

dummdidumm

thank you!

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@5.56.1 ### Patch Changes - fix: error at compile time on duplicate snippet/declaration tag definitions ([#18351](#18351)) - fix: parse declaration tag contents more robustly ([#18353](#18353)) - fix: correctly transform references to earlier declarators in a declaration tag (e.g. `{let a = $state(0), b = $derived(a * 2)}`) ([#18348](#18348)) - fix: avoid spurious `state_referenced_locally` warnings for `$derived` declarations in declaration tags ([#18348](#18348)) - fix: tolerate whitespace before `let`/`const` in declaration tags ([#18348](#18348)) - fix: prevent infinite loop when a tag's expression ends with a trailing `/` at the end of the input ([#18350](#18350)) - fix: more robust parsing of declaration tags with regards to `type` ([#18330](#18330)) - fix: preserve newlines in spread input values when the `type` attribute is applied after `value` ([#18345](#18345)) - fix: update `SvelteURLSearchParams` when setting duplicate keys to the same joined value ([#18336](#18336)) - fix: check references for blockers on server, too ([#18352](#18352)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

This PR contains the following updates: | Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) | |---|---|---|---| | [svelte](https://svelte.dev) ([source](https://github.com/sveltejs/svelte/tree/HEAD/packages/svelte)) | [`5.56.0` → `5.56.1`](https://renovatebot.com/diffs/npm/svelte/5.56.0/5.56.1) | ![age](https://developer.mend.io/api/mc/badges/age/npm/svelte/5.56.1?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/svelte/5.56.0/5.56.1?slim=true) | --- ### Release Notes <details> <summary>sveltejs/svelte (svelte)</summary> ### [`v5.56.1`](https://github.com/sveltejs/svelte/blob/HEAD/packages/svelte/CHANGELOG.md#5561) [Compare Source](https://github.com/sveltejs/svelte/compare/svelte@5.56.0...svelte@5.56.1) ##### Patch Changes - fix: error at compile time on duplicate snippet/declaration tag definitions ([#18351](sveltejs/svelte#18351)) - fix: parse declaration tag contents more robustly ([#18353](sveltejs/svelte#18353)) - fix: correctly transform references to earlier declarators in a declaration tag (e.g. `{let a = $state(0), b = $derived(a * 2)}`) ([#18348](sveltejs/svelte#18348)) - fix: avoid spurious `state_referenced_locally` warnings for `$derived` declarations in declaration tags ([#18348](sveltejs/svelte#18348)) - fix: tolerate whitespace before `let`/`const` in declaration tags ([#18348](sveltejs/svelte#18348)) - fix: prevent infinite loop when a tag's expression ends with a trailing `/` at the end of the input ([#18350](sveltejs/svelte#18350)) - fix: more robust parsing of declaration tags with regards to `type` ([#18330](sveltejs/svelte#18330)) - fix: preserve newlines in spread input values when the `type` attribute is applied after `value` ([#18345](sveltejs/svelte#18345)) - fix: update `SvelteURLSearchParams` when setting duplicate keys to the same joined value ([#18336](sveltejs/svelte#18336)) - fix: check references for blockers on server, too ([#18352](sveltejs/svelte#18352)) </details> --- ### Configuration 📅 **Schedule**: (UTC) - Branch creation - At any time (no schedule defined) - Automerge - At any time (no schedule defined) 🚦 **Automerge**: Disabled because a matching PR was automerged previously. ♻ **Rebasing**: Whenever PR is behind base branch, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this PR, check this box --- This PR has been generated by [Mend Renovate](https://github.com/renovatebot/renovate).  Co-authored-by: huskas-2189 <huskas-2189@noreply.codeberg.org> Reviewed-on: https://codeberg.org/huskas-2189/Bookmark/pulls/82

fix: parse declaration tags with a division operator in the initializer

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vercel Bot reviewed Jun 1, 2026

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Comment thread packages/svelte/src/compiler/phases/1-parse/acorn.js Outdated

dummdidumm added 2 commits June 1, 2026 23:21

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changeset tweak

d8e126d

dummdidumm approved these changes Jun 1, 2026

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dummdidumm merged commit 2afb895 into sveltejs:main Jun 1, 2026
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github-actions Bot mentioned this pull request Jun 1, 2026

Version Packages #18346

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github-actions Bot mentioned this pull request Jun 2, 2026

Upgrade Svelte submodule to 5.56.1 baseballyama/rsvelte#639

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fix: parse declaration tags with a division operator in the initializer#18353

fix: parse declaration tags with a division operator in the initializer#18353
dummdidumm merged 4 commits into
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hjaber:fix/declaration-tag-division

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