fix(lint): suppress false positives in noUnusedVariables for Svelte store subscriptions and $bindable() props

[Mokto]

Depends on #10473 — this PR should not be merged until that one lands. Once it does, the diff here will reduce to only the two commits below.

Summary

Two false-positive patterns in noUnusedVariables for Svelte files, both building on the cross-script reference tracking introduced in #10473.

1. Svelte store auto-subscription

When a variable is declared in <script> and only used in the template via Svelte's $store auto-subscription syntax, it was incorrectly flagged as unused:

<script>
  const { form, errors } = superForm(...);
  // $form used in script → not flagged ✓
  // $errors only in template → was falsely flagged ✗
</script>
<input bind:value={$form.email} errors={$errors.email} />

Fix: when collecting template references in EmbeddedValueReferencesBuilder, in Svelte mode, $-prefixed identifiers that are not runes ($state, $derived, etc.) also register the store name without the $ prefix.

2. Svelte 5 $bindable() props

Variables declared as = $bindable() in a $props() destructuring and only assigned to (never read) were flagged as unused. In Svelte 5, assigning to a $bindable() prop reflects the value back to the parent — the write IS the observable use.

<script>
  let { backButton = $bindable() } = $props();
  backButton = { label: 'Back', onClick: goBack }; // write → reflected to parent
</script>

Fix: in no_unused_variables.rs, when the binding is a shorthand property whose default initializer is $bindable() and whose enclosing declarator is initialized from $props(), suppress the diagnostic.

This PR was written primarily by Claude Code.

Test Plan

New fixtures valid-svelte-store-subscription.svelte and valid-svelte-bindable-props.svelte added to noUnusedVariables test specs. All existing tests pass.

Docs

N/A

[changeset-bot]

🦋 Changeset detected

Latest commit: 2e2bc63

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

Name	Type
@biomejs/biome	Patch
@biomejs/cli-win32-x64	Patch
@biomejs/cli-win32-arm64	Patch
@biomejs/cli-darwin-x64	Patch
@biomejs/cli-darwin-arm64	Patch
@biomejs/cli-linux-x64	Patch
@biomejs/cli-linux-arm64	Patch
@biomejs/cli-linux-x64-musl	Patch
@biomejs/cli-linux-arm64-musl	Patch
@biomejs/wasm-web	Patch
@biomejs/wasm-bundler	Patch
@biomejs/wasm-nodejs	Patch
@biomejs/backend-jsonrpc	Patch

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[coderabbitai]

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📒 Files selected for processing (3)

• crates/biome_js_analyze/src/lint/correctness/no_unused_variables.rs
• crates/biome_js_analyze/src/services/embedded.rs
• crates/biome_workspace_db/src/embedded/references.rs

👮 Files not reviewed due to content moderation or server errors (3)

• crates/biome_js_analyze/src/lint/correctness/no_unused_variables.rs
• crates/biome_workspace_db/src/embedded/references.rs
• crates/biome_js_analyze/src/services/embedded.rs

---

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarises the main change: suppressing noUnusedVariables false positives for Svelte subscriptions and $bindable() props.
Description check	✅ Passed	The description is clearly related to the changeset and matches the Svelte lint fix and tests.
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.

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In @.changeset/fix-svelte-store-bindable.md:
- Line 5: The changeset description in the markdown file needs the required
bugfix prefix format. Update the opening sentence so it starts with Fixed
[`#NUMBER`](issue link): followed by the summary, while keeping the existing
noUnusedVariables rule link in the rest of the text. Make sure the description
also includes the issue link and preserves the references to the Svelte store
subscription and $bindable() false-positive fix.

In `@crates/biome_js_analyze/src/lint/correctness/no_unused_variables.rs`:
- Around line 449-456: The $bindable() suppression in no_unused_variables
currently hides all bindable props from $props(), even when they are never used,
so tighten the check to only return None for write-only bindings. Update the
logic around is_svelte_bindable_prop(binding) in the unused-variable diagnostic
path to require an explicit write-only usage condition before suppressing, and
mirror the same fix anywhere else the same suppression is applied. Add a
regression test covering a $bindable() prop that is neither read nor written so
it still reports unused.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

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⛔ Files ignored due to path filters (2)

• crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/valid-svelte-bindable-props.svelte.snap is excluded by !**/*.snap and included by **
• crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/valid-svelte-store-subscription.svelte.snap is excluded by !**/*.snap and included by **

📒 Files selected for processing (6)

• .changeset/fix-svelte-store-bindable.md
• crates/biome_js_analyze/src/lint/correctness/no_unused_variables.rs
• crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/valid-svelte-bindable-props.svelte
• crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/valid-svelte-store-subscription.svelte
• crates/biome_service/src/workspace/document/services/embedded_value_references.rs
• crates/biome_service/src/workspace/server.rs

[coderabbitai]

📐 Maintainability & Code Quality | 🟡 Minor | ⚡ Quick win

Use the required bugfix prefix with an issue link.

For bug fixes, this should start with Fixed [#NUMBER](issue link): ...; keep the rule link in the rest of the sentence.
As per coding guidelines, "for bug fixes start with 'Fixed [#NUMBER](issue link): ...'" and "include issue links, rule links, and assist links in changeset descriptions." Based on learnings, Biome changesets require the exact Fixed [#NUMBER](issue link): ... prefix format.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In @.changeset/fix-svelte-store-bindable.md at line 5, The changeset description
in the markdown file needs the required bugfix prefix format. Update the opening
sentence so it starts with Fixed [`#NUMBER`](issue link): followed by the summary,
while keeping the existing noUnusedVariables rule link in the rest of the text.
Make sure the description also includes the issue link and preserves the
references to the Svelte store subscription and $bindable() false-positive fix.

Sources: Coding guidelines, Learnings

[coderabbitai]

🎯 Functional Correctness | 🟠 Major | ⚡ Quick win

Gate $bindable() suppression to write-only bindings only.

This currently suppresses any unused $bindable() prop from $props(), including truly untouched ones, which can create false negatives. Please require a write-only usage condition before returning None, and add a regression case where a $bindable() prop is never read or written.

Also applies to: 703-738

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@crates/biome_js_analyze/src/lint/correctness/no_unused_variables.rs` around
lines 449 - 456, The $bindable() suppression in no_unused_variables currently
hides all bindable props from $props(), even when they are never used, so
tighten the check to only return None for write-only bindings. Update the logic
around is_svelte_bindable_prop(binding) in the unused-variable diagnostic path
to require an explicit write-only usage condition before suppressing, and mirror
the same fix anywhere else the same suppression is applied. Add a regression
test covering a $bindable() prop that is neither read nor written so it still
reports unused.

[codspeed-hq]

Merging this PR will not alter performance

✅ 58 untouched benchmarks
⏩ 196 skipped benchmarks¹

---

_{Comparing Mokto:fix/svelte-store-subscription-unused (2e2bc63) with main (f1d3877)}

Footnotes

1. 196 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[ematipico]

Hey @Mokto can you rebase the branch and address linting?