[robhogan]

Summary

Since #59580, a u regex with a named backreference directly followed by a digit fails Hermes compilation with Invalid regular expression: Invalid escape.

The cause is @babel/plugin-transform-named-capturing-groups-regex, which rewrites \k<name> as a numbered backreference without guarding a following digit:

/(?<a>.)\k<a>1/u  ->  _wrapRegExp(/(.)\11/u, {a: 1})

\11 is then a reference to group 11, a syntax error in u mode. Before #59580 the unicode transform also dropped the u flag, and without it \11 reads as a legacy octal escape (a tab) - so these regexes compiled, but silently matched the wrong thing. Non-u regexes still have that miscompile on main.

Hermes V1 supports named capturing groups natively, so this stops lowering them for the Hermes profiles. The exception is a name repeated across alternatives (/(?<y>\d{4})-\d\d|\d\d-(?<y>\d{4})/), which Hermes doesn't support, so those regexes alone still go through @babel/plugin-transform-duplicate-named-capturing-groups-regex. Native groups also drop the _wrapRegExp helper, a RegExp subclass with a WeakMap lookup on every match.

The hermes-legacy and default profiles keep the transform, and the bug, which is in regexpu-core (still present in 6.5.3).

Test plan

• New unit tests. The kitchen-sink snapshots for the Hermes V1 configurations change only in the named-group regex and the removed helper.
• Hermes 260318099.0.4 passes test262's named groups, regex literal, exec, @@replace, @@matchAll, matchAll, replaceAll and match indices tests (413 run, no failures).
• AI-driven: compiled the preset's hermes-stable output with hermesc and compared against Node 26 for \k<a>1 with and without u, a repeated-name regex, .groups and $<name> replacement - all match. Before this change, the u case failed to compile and the non-u case matched "x\t" instead of "xx1".

Changelog

[General][Fixed] - Babel preset: Hermes V1 profiles no longer lower named capturing groups, fixing named backreferences followed by a digit

[github-actions]

Visual regression

13 visual difference(s) at 3ff60cc0130a. Visual differences need maintainer approval. Review the report, then apply visual-change-approved.

android button/color-red/default: Size changed, 1080×1883 → 1080×1956

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android button/default-styling/default: Size changed, 1080×1883 → 1080×1956

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android button/disabled/default: Size changed, 1080×1883 → 1080×1956

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android button/two-buttons-flexbox/default: Size changed, 1080×1883 → 1080×1956

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android switch/basic/default: Size changed, 1080×1883 → 1080×1956

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android switch/basic/toggled: Size changed, 1080×1883 → 1080×1956

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android switch/custom-colors/default: Size changed, 1080×1883 → 1080×1956

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android switch/custom-colors/toggled: Size changed, 1080×1883 → 1080×1956

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android switch/disabled/default: Size changed, 1080×1883 → 1080×1956

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android touchable/feedback-events/pressed: Changed, 995 px (0.220%)

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android touchable/without-feedback/default: Size changed, 1080×1883 → 1080×1956

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android touchable/without-feedback/pressed: Size changed, 1080×1883 → 1080×1956

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ios button/default-styling/default: Changed, 38223 px (1.533%)

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