bug#66395: 28.2; Todo-mode locks up when trying to edit an entry

[Stephen Berman <stephen.berman@gmx.net>]

On Sat, 7 Oct 2023 19:06:55 +0000 "Nathan R. DeGruchy" <nathan@degruchy.org> wrote:

> I am trying to explore using 'todo-mode' as a todo list and while I can
> see and create entries in todo-mode using the normal functions, trying
> to edit an item seems to cause emacs to soft-lock. I can reproduce this
> in a config-less emacs via `emacs -Q`.
>
> Basically, I have a todo-file at $HOME/.config/emacs/todo/tasks.todo,
> this was created when using `todo-show` initially. The contents are not
> very complex:
>
> (("Emacs" . [1 0 0 0]) ("Home" . [1 0 0 0]))
> --==-- Emacs
> [2023-10-07] Learn Todo Mode
>
> ==--== DONE
> --==-- Home
> [2023-10-07] Get new wiper blades
>
> ==--== DONE
>
> When on either of the items, if I hit 'e' to edit them, it causes emacs
> to lock up, specifically around `todo-done-item-p()`. I found this out
> by enabling `toggle-debug-on-quit`, reproducing the error, and the
> C-g'ing out of the loop/lockup. I also tried to trace through the
> todo-edit-item with edebug-defun. Stepping through, it seems to reach
> the same predicate function and ... stop.
>
> I'm not sure where to go from here.

On Sat, 07 Oct 2023 14:37:00 -0500 LdBeth <andpuke@foxmail.com> wrote:

> As we have discussed on IRC, the nonstandard timestamp format is the cause.

Yes.  This is a duplicate of bug#55284.  At the time that bug was
reported, I didn't have time to try fixing it (being the todo-mode
maintainer), and later, unfortunately, I forgot about it.  I'll try to
look into it soon, but, as I noted in that bug thread, I think it's not
easy to fix.  One issue is that todo-mode basically employs the same
handling of date formats as diary-lib.el, and the ISO date style causes
problems there too, see bug#55286.

> The hang is cause by the while loop `todo-item-start' not properly handle fail
> case, however.
>
> This patch would at least fix the hang.
>
> ---
> LdBeth
>
> --- todo-mode.el.old	2023-10-07 14:28:59.000000000 -0500
> +++ todo-mode.el	2023-10-07 14:30:20.000000000 -0500
> @@ -5242,8 +5242,8 @@
>  	   ;; Buffer is widened.
>  	   (looking-at (regexp-quote todo-category-beg)))
>      (goto-char (line-beginning-position))
> -    (while (not (looking-at todo-item-start))
> -      (forward-line -1))
> +    (while (and (not (looking-at todo-item-start))
> +                (= (forward-line -1) 0)))
>      (point)))
>
>  (defun todo-item-end ()

Thanks.  Even though this doesn't eliminate other problems with using
the ISO date style in todo-mode (or in the Emacs Diary), since it does
prevent the infinite loop here, it may be a good stopgap.

Steve Berman