fix(linter/no-unused-vars): correctly detect unused symbols in TypeScript namespaces

[camc314]

Fix detection of unused symbols inside TypeScript namespaces and declared modules:

• Functions inside non-declared namespaces are now correctly reported as unused
• Types inside declared modules with explicit exports are now correctly reported as unused
• Symbols inside exported namespaces are no longer incorrectly considered exported

fixes #17122

[camc314]

• fix(linter/no-unused-vars): correctly detect unused symbols in TypeScript namespaces #17129 👈 (View in Graphite)
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #17129 will not alter performance

_{Comparing c/12-19-fix_linter_no-unused-vars_correctly_detect_unused_symbols_in_typescript_namespaces (6faf625) with main (adb41ba)}

Summary

✅ 4 untouched
⏩ 41 skipped¹

Footnotes

1. 41 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. ↩

[camc314]

Merge activity

• Dec 19, 7:05 PM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Dec 19, 7:11 PM UTC: camc314 added this pull request to the Graphite merge queue.
• Dec 19, 7:16 PM UTC: Merged by the Graphite merge queue.

[Copilot]

Pull request overview

This PR fixes the detection of unused symbols in TypeScript namespaces and declared modules to correctly identify unused functions, types, and interfaces according to their context.

Key changes:

• Functions inside non-declared namespaces are now correctly reported as unused
• Type aliases inside declared modules with explicit exports are now correctly reported as unused
• Symbols inside exported namespaces are no longer incorrectly considered exported by virtue of the namespace being exported

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
crates/oxc_linter/src/snapshots/eslint_no_unused_vars@oxc-namespaces.snap	Updated snapshot to include detection of unused function foo in exported namespace
crates/oxc_linter/src/rules/eslint/no_unused_vars/tests/typescript_eslint.rs	Re-enabled test case for declare module 'foo' with unused type to verify fix
crates/oxc_linter/src/rules/eslint/no_unused_vars/tests/oxc.rs	Added comprehensive test cases for various namespace and module scenarios, including exported declared namespaces and modules
crates/oxc_linter/src/rules/eslint/no_unused_vars/mod.rs	Extended type alias handling to match interface declaration behavior in declared modules
crates/oxc_linter/src/rules/eslint/no_unused_vars/ignored.rs	Refined function ignoring logic to check for ambient context when TypeScript syntax or body-less functions are encountered
crates/oxc_linter/src/rules/eslint/no_unused_vars/allowed.rs	Enhanced namespace checking to distinguish between ambient namespaces with and without explicit exports, ensuring only truly ambient symbols without exports are automatically allowed

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