Bug #22429: regex empty capture group in a counted loop prevents a match

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: ruby 4.0.7 (2026-09-15 revision 229531a6cf) +PRISM [arm64-darwin27]
• Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN

[robertmorelli (Robert Morelli)]

repro:

/\A(?:(){1,2}?a)+\z/.match?("aa")     # false
/\A(?:(?:){1,2}?a)+\z/.match?("aa")   # true
/\A(?:(){1,2}a)+\z/.match?("aa")      # true

An empty capture () behaves differently from (?:). Perl, Python and Oniguruma 6.9.10 return true for all three.