fix(lint): noUnusedVariables should ignore type parameters in ambient context

[wataryooou]

Summary

• Fix noUnusedVariables so type parameters declared in ambient contexts (e.g., within declare module) are not reported as unused, aligning behavior with TypeScript/ESLint expectations.
• Add a regression case using a common module augmentation example (declare module "react") to cover this scenario.
• Include a changeset (.changeset/calm-ambient-type-params.md) since this is user-visible behavior.

Test Plan

• cargo test -p biome_js_analyze --test spec_tests -- specs::correctness::no_unused_variables::valid_ambient_type_param_ts

Docs

• No new options added; behavior correction only.
• If desired for release notes: “Fixed noUnusedVariables incorrectly flagging ambient type parameters as unused.”

Playground link

https://biomejs.dev/playground/?lintRules=noUnusedVariables&code=ZABlAGMAbABhAHIAZQAgAG0AbwBkAHUAbABlACAAIgByAGUAYQBjAHQAIgAgAHsACgAgACAAZQB4AHAAbwByAHQAIABpAG4AdABlAHIAZgBhAGMAZQAgAEMAbwBtAHAAbwBuAGUAbgB0AE0AZQB0AGEAPABUAD4AIAB7AAoAIAAgACAAIABkAGkAcwBwAGwAYQB5AE4AYQBtAGUAPwA6ACAAcwB0AHIAaQBuAGcAOwAKACAAIAAgACAAdgBlAHIAcwBpAG8AbgA%2FADoAIABzAHQAcgBpAG4AZwA7AAoAIAAgAH0ACgAKACAAIABlAHgAcABvAHIAdAAgAGkAbgB0AGUAcgBmAGEAYwBlACAASABvAG8AawBSAGUAcwB1AGwAdAA8AFQAPgAgAHsACgAgACAAIAAgAGUAcgByAG8AcgA%2FADoAIABFAHIAcgBvAHIAIAB8ACAAbgB1AGwAbAA7AAoAIAAgACAAIABpAHMATABvAGEAZABpAG4AZwA6ACAAYgBvAG8AbABlAGEAbgA7AAoAIAAgAH0ACgB9AA%3D%3D&language=ts

[changeset-bot]

🦋 Changeset detected

Latest commit: 44261d5

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

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[coderabbitai]

Walkthrough

This pull request refines the noUnusedVariables lint rule to handle TypeScript type parameters in ambient contexts correctly. The fix modifies the rule to skip suggesting prefix underscore for type parameters declared within ambient blocks (such as declare module statements), rather than treating them uniformly. A test file with ambient module declarations for React is added to validate the behaviour.

Suggested labels

A-Linter, L-JavaScript

Suggested reviewers

• dyc3
• ematipico

Pre-merge checks and finishing touches

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and concisely describes the main change: fixing noUnusedVariables to ignore type parameters in ambient contexts.
Description check	✅ Passed	The pull request description clearly describes the changeset: fixing noUnusedVariables to ignore type parameters in ambient contexts, adding a regression test, and including a changeset file.

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[codspeed-hq]

CodSpeed Performance Report

Merging #8561 will not alter performance

_{Comparing wataryooou:fix/no-unused-variables-type-params (44261d5) with main (d80fa41)¹}

Summary

✅ 58 untouched
⏩ 95 skipped²

Footnotes

1. No successful run was found on main (25cdd50) during the generation of this report, so d80fa41 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 95 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. ↩

[arendjr]

Thank you!