fix(linter/plugins): handle utf16 characters within comment spans

[lilnasy]

Part of #14564. Corrects start and end offsets to accommodate two byte characters. Conversion of UTF-8 indices to UTF-16 takes place on the rust side for performance.

[graphite-app]

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[codspeed-hq]

CodSpeed Performance Report

Merging #14768 will not alter performance

_{Comparing lilnasy:fix/linter/plugins/utf16 (baf7192) with main (c6395c7)¹}

Summary

✅ 4 untouched
⏩ 33 skipped²

Footnotes

1. No successful run was found on main (cd266b4) during the generation of this report, so c6395c7 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

2. 33 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. ↩

[Copilot]

Pull Request Overview

This PR fixes UTF-16 character handling within comment spans for the linter plugin system. When source code contains multi-byte UTF-16 characters (like emojis or non-Latin scripts), comment span offsets need to be correctly converted from UTF-8 to UTF-16 indices to ensure accurate positioning.

Key Changes:

• Added UTF-16 conversion for comment spans in the linter
• Introduced comprehensive test coverage for Unicode characters in comments

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/lib.rs	Added call to convert comment spans to UTF-16 offsets
apps/oxlint/test/fixtures/unicode-comments/plugin.ts	New test plugin that reports all comments with their types and values
apps/oxlint/test/fixtures/unicode-comments/output.snap.md	Expected snapshot output showing correctly extracted comments with Unicode characters
apps/oxlint/test/fixtures/unicode-comments/files/unicode-comments.js	Test fixture file containing various Unicode characters in comments (emojis, Chinese, Greek, Hebrew, etc.)
apps/oxlint/test/fixtures/unicode-comments/.oxlintrc.json	Configuration file enabling the unicode-comments test plugin
apps/oxlint/test/e2e.test.ts	Added end-to-end test case for UTF-16 character handling in comments

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[overlookmotel]

Great stuff!

All looks correct, so merging. But I'd suggest as follow-up to expand the tests:

• Add start and end of each comment to snaphot.
• Add range to snapshot (or assert comment.range[0] === comment.start && comment.range[1] === comment.end for all comments).
• Add loc to snapshot for each comment, and eyeball that they look correct.

It might also be good to call context.report() for each comment individually, passing the Comment as node property. That'd:

1. Test the translation of offsets back to UTF-8 when reporting errors (that happens on Rust side).
2. Make the snapshot more readable and easier to eyeball for errors.

[lilnasy]

@overlookmotel I left out testing start and end explicitly for brevity. The comments' value being correct implies they were correct when used to slice sourceText. I can add the assertions and loc right away!