bug#72759: 31.0.50; Emacs hangs with open-paren-in-column-0-is-defun-start set to nil

[Eli Zaretskii <eliz@gnu.org>]

> From: Eshel Yaron <me@eshelyaron.com>
> Cc: 72759@debbugs.gnu.org
> Date: Thu, 22 Aug 2024 17:49:22 +0200
> 
> After taking another look, ISTM that the problem is that checkdoc
> assumes that beginning-of-defun either advances point or returns nil,
> but since beginning-of-defun unconditionally moves to the beginning of
> the line, it can in fact find a defun ahead of point (and thus return
> non-nil) but then move back to the beginning of the line, so point is
> unchanged.  So the assumption in checkdoc doesn't always hold when
> open-paren-in-column-0-is-defun-start is nil.  This assumption should
> still hold, however, for beginning-of-defun-raw, which doesn't go back
> to the beginning of the line.
> 
> This suggests the following change, which indeed seems to fix the hang:
> 
> 
> diff --git a/lisp/emacs-lisp/checkdoc.el b/lisp/emacs-lisp/checkdoc.el
> index 949ca6b74ad..65226d8ee44 100644
> --- a/lisp/emacs-lisp/checkdoc.el
> +++ b/lisp/emacs-lisp/checkdoc.el
> @@ -981,7 +981,7 @@ checkdoc-next-docstring
>  Return nil if there are no more doc strings."
>    (let (found)
>      (while (and (not (setq found (checkdoc--next-docstring)))
> -                (beginning-of-defun -1)))
> +                (beginning-of-defun-raw -1)))
>      found))

But the doc string of beginning-of-defun-raw says, inter alia:

  This is identical to function `beginning-of-defun', except that point
  does not move to the beginning of the line when `defun-prompt-regexp'
  is non-nil.                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
  ^^^^^^^^^^

Does that mean defun-prompt-regexp was non-nil in your case?  The
default is nil.