fix(core): treat {@const} and {let}/{const} declaration tags as shadowing bindings

[oekazuma]

Summary

Follow-up flagged by the final review of #285: scopeIntroducedNames did not treat template declaration tags as scope-introducing, so a write to a template-local alias was misattributed to a same-named top-level $state binding. Covers {@const ...} (ConstTag) and the newer {let ...} / {const ...} declaration tags (DeclarationTag, svelte.dev/docs/svelte/declaration-tags — AST shape verified against svelte 5.56). Verified false positive before this fix:

<script>
  let tags = $state(new Set());
</script>
{#each groups as g}
  {@const tags = g.tags}  <!-- same for {let tags = g.tags} / {const tags = g.tags} -->
  <button onclick={() => tags.add('x')}>x</button>
{/each}

correctness/nonreactive-builtin-state flagged the outer tags, and the same misattribution suppressed correctness/unmutated-state's constableStates.

Change

One addition to the shared scopeIntroducedNames helper: a Fragment's own ConstTag/DeclarationTag declarations now shadow the whole fragment (same over-conservative whole-scope model as a block's let; both node types carry the same declaration.declarations shape, so one branch covers all three tags). A write to one of these template-locals — possible for {let} — is still not a write to the outer binding, so the fix is strictly precision-improving for every consumer of the helper (all component-analysis collectors) at once.

Testing

• Four regression tests (nonreactive-builtin-state facts for {@const}/{let}/{const} + constableStates for {@const} mutation and {let} reassignment), each verified to fail without the fix and pass with it
• core 668 and cli 703 tests green; tsc, oxlint, oxfmt clean
• Changeset: patch × core / cli / vite / mcp

🤖 Generated with Claude Code

[coderabbitai]

📝 Walkthrough

Walkthrough

Fragment-level {@const} declarations are now included in scope shadowing, preventing writes through same-named aliases from being attributed to outer $state variables. Parser tests cover constableStates and nonreactiveBuiltinStates, with patch releases recorded.

Changes

Fragment const shadowing

Layer / File(s)	Summary
Recognize fragment const bindings packages/core/src/component-parse.ts	scopeIntroducedNames now records identifiers declared by fragment-level {@const} tags as shadowed names.
Validate shadowed mutation analysis packages/core/test/*parse.test.ts, .changeset/const-tag-scope-shadow.md	Tests verify that mutations through {@const} aliases do not affect outer state analysis, and patch releases are recorded for the affected packages.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• oekazuma/svelte-vitals#141: Adds related scope-aware shadow tracking to prevent writes from being attributed to outer bindings.
• oekazuma/svelte-vitals#267: Expands template-scope shadowing in the same scopeIntroducedNames function.
• oekazuma/svelte-vitals#285: Adds related parsing tests for state mutation attribution.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title matches the core change around shadowing bindings, though it is broader than the patch and mentions tags not clearly changed here.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

---

_{Comment @coderabbitai help to get the list of available commands.}