feat(parser): improve diagnostic for unexpected optional declarations

[camchenry]

Currently we just emit "unexpected token", but we actually have a good amount of context here to provide better help + error message.

[camchenry]

• perf(parser): remove bounds check for getting strings from lexer #16135
• feat(parser): add diagnostic for JSX identifiers with hyphens #16133
• feat(parser): add diagnostic for expected ident after optional chain #16132
• feat(parser): improve diagnostic for unexpected optional declarations #16131 👈 (View in Graphite)
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #16131 will not alter performance

_{Comparing 11-25-feat_parser_improve_diagnostic_for_unexpected_optional_declarations (dfa63e3) with main (891e0b4)}

Summary

✅ 42 untouched
⏩ 3 skipped¹

Footnotes

1. 3 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 enhances parser diagnostics by replacing a generic "Unexpected token" error with a more specific and helpful message when encountering optional declarations (?) in variable declarations where they are not allowed. The improvement provides clear guidance to developers by explaining the issue and suggesting a fix.

• Adds a new diagnostic function unexpected_optional_declaration with contextual error messaging
• Updates the variable declaration parser to use the improved diagnostic
• Adds helpful suggestion to remove the ? token

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
crates/oxc_parser/src/diagnostics.rs	Adds unexpected_optional_declaration function following established diagnostic patterns with clear error message and help text
crates/oxc_parser/src/js/declaration.rs	Updates variable declarator parsing to use the new specific diagnostic instead of generic unexpected_token
tasks/coverage/snapshots/parser_misc.snap	Updates test snapshots showing improved error messages for all affected test cases (oxc-2253.ts and oxc-5955-1.ts)

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[graphite-app]

Merge activity

• Nov 26, 4:30 AM UTC: Boshen added this pull request to the Graphite merge queue.
• Nov 26, 4:38 AM UTC: Merged by the Graphite merge queue.