fix(minifier): validate RegExp patterns before marking as pure

[Boshen]

Summary

Invalid RegExp patterns like RegExp("[") or invalid flags like RegExp("a", "xyz") throw SyntaxError at runtime, but the minifier was incorrectly removing them.

This change uses oxc_regular_expression to validate patterns at compile time:

• Valid patterns are marked as pure and can be removed when unused
• Invalid patterns or non-literal arguments are kept (preserving runtime errors)

Behavior

Input	Valid?	Removed?
RegExp()	✅	✅
RegExp('a', 'g')	✅	✅
RegExp(/foo/)	✅	✅
RegExp('[')	❌	❌ (throws SyntaxError)
RegExp('a', 'xyz')	❌	❌ (throws SyntaxError)
RegExp(variable)	?	❌ (can't determine)

Fixes #18050

Test plan

• Updated existing tests to reflect correct behavior
• Added tests for invalid patterns and flags
• cargo test -p oxc_minifier passes
• cargo test -p oxc_ecmascript passes

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes a bug where the minifier incorrectly removed invalid RegExp patterns that should throw SyntaxError at runtime. The fix uses the oxc_regular_expression parser to validate patterns and flags at compile time, ensuring that only valid RegExp constructors are marked as pure and can be safely removed.

Changes:

• Added is_valid_regexp function that validates RegExp patterns and flags using the regex parser
• Updated minifier's normalize pass to use validation for RegExp constructor calls
• Updated tests to reflect correct behavior for valid/invalid patterns

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
crates/oxc_ecmascript/src/side_effects/expressions.rs	Implements is_valid_regexp validation function using the regex parser
crates/oxc_ecmascript/src/side_effects/mod.rs	Exports the new is_valid_regexp function
crates/oxc_minifier/src/peephole/normalize.rs	Integrates RegExp validation in the normalize pass for NewExpression
crates/oxc_ecmascript/Cargo.toml	Adds oxc_regular_expression dependency
Cargo.lock	Updates lock file with new dependency
crates/oxc_minifier/tests/peephole/substitute_alternate_syntax.rs	Updates tests with correct behavior for valid/invalid RegExp patterns
crates/oxc_minifier/tests/peephole/normalize.rs	Updates tests to handle non-literal RegExp arguments correctly
crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs	Adds tests for invalid patterns and flags

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[codspeed-hq]

Merging this PR will not alter performance

✅ 42 untouched benchmarks
⏩ 3 skipped benchmarks¹

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_{Comparing fix/minifier-regexp-validation (38e4b53) with main (91126a0)²}

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. ↩

2. No successful run was found on main (2ae523c) during the generation of this report, so 91126a0 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[Boshen]

Merge activity

• Jan 18, 1:47 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Jan 18, 1:47 AM UTC: Boshen added this pull request to the Graphite merge queue.
• Jan 18, 1:58 AM UTC: The Graphite merge queue couldn't merge this PR because it was not satisfying all requirements (Failed CI: 'Conformance').
• Jan 18, 4:28 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Jan 18, 4:30 AM UTC: Boshen added this pull request to the Graphite merge queue.
• Jan 18, 4:31 AM UTC: Merged by the Graphite merge queue.