bug#58726: 29.0.50; Bug in regexp matching with shy groups

[Michael Heerdegen]

Hello,

  (string-match-p "\\`\\(?:ab\\)*\\'" "a") ==> 0

That's wrong, the expected result is nil.  The language matched by that
regexp is {"", "ab", "abab", "ababab", ...}.

Changing to a non-shy group doesn't exploit the issue:

  (string-match-p "\\`\\(ab\\)*\\'" "a")  ==> nil

as expected.

I've been told (emacs-help, Bruno Barbier) that the problem exists at
least in emacs 27, emacs 28 and emacs 29.


TIA,

Michael.