bug#45944: 28.0.50; Mailabbrev sometimes hangs

[Lars Ingebrigtsen <larsi@gnus.org>]

Katsumi Yamaoka <yamaoka@jpl.org> writes:

> As far as I can observe, the more "____" line is long, the more
> it takes a long time.

Curious.  I can reproduce this with the example code, but the function
that's hanging is apparently just doing:

(re-search-forward (concat "^" mail-citation-prefix-regexp ".*$") nil t)

When I try this manually, then it doesn't hang, which is the curious
thing?  So why is it hanging from a syntax-propertize perspective but
not when called directly?

Debugger entered--Lisp error: (quit)
  search-forward-regexp("^\\([ \11]*\\(\\w\\|[_.]\\)+>+\\|[ \11]*[>|]\\)+.*$" 100 noerror)
  (while (search-forward-regexp citation-regexp end 'noerror) (let ((
  (let ((citation-regexp (concat "^" message-cite-prefix-regexp ".*$"
  message--syntax-propertize(1 100)
  syntax-propertize(100)
  internal--syntax-propertize(7)
  abbrev--before-point()

Anyway, this is the regexp in question:

(defcustom mail-citation-prefix-regexp
  (purecopy "\\([ \t]*\\(\\w\\|[_.]\\)+>+\\|[ \t]*[>|]\\)+")

And I guess there's some extreme backtracking going on with the

  \\(\\w\\|[_.]\\)+>

part?

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