bug#61629: master: Sometimes M-x imenu throws an error when there's a single function in the buffer.

[Alan Mackenzie <acm@muc.de>]

Bug fixed in master.

On Sun, Feb 19, 2023 at 15:39:13 +0000, Alan Mackenzie wrote:
> On the master branch, the recipe below leads to an error being thrown
> from imenu.

> Awareness of this bug resulted from the thread Subject: Error in C++
> Mode with Emacs 27.0.90, Date: Tue 24 Mar 2020, From: Angelo Graziosi.
> This thread reported a bug in imenu, which never made it to debbugs, but
> which was partially fixed.

> Thanks to Dmitry Gutov, who made me aware of the bit that didn't get
> fixed then.

> To reproduce the error in the master branch:
> (i) emacs -Q in a GUI environment.
> (ii) Evaluate the following:

> ;; C/C++ modes
> (defun my-c-mode ()
>   "My customization for `c-mode' and `c++-mode'."
>   ;; Add index of func. to menu bar
>   (imenu-add-to-menubar "Functions"))

> ;; c++-mode
> (add-hook 'c-mode-common-hook 'my-c-mode)

> (setq imenu-auto-rescan t)
> (setq imenu-use-popup-menu t)

> (iii) Type the following into an empty C++ buffer called graziosi.cc:

> int main ()
> {
>     return 0;
> }

> (iv) M-x imenu<RET>.

> This throws the error "Wrong type argument: seqencep, #<marker at 1 in
> graziosi.cc>".  This is a bug.

-- 
Alan Mackenzie (Nuremberg, Germany).