bug#44068: 28.0.50; Faulty uses of tabulated-list-format

[Stephen Berman]

On Mon, 19 Oct 2020 00:17:12 +0200 Stephen Berman <stephen.berman@gmx.net> 
wrote:

> On Sun, 18 Oct 2020 15:01:31 -0700 Stefan Kangas <stefankangas@gmail.com> 
> wrote:
[...]
>> Thanks for the patch.  I've tested it and it indeed fixes several bugs
>> in this area.
>>
>> But it got me thinking: for the final column at least, maybe we should
>> just make tabulated-list-mode work as advertised, and itself figure out
>> that it should use this length?  That way, we would solve any bugs also
>> for external packages that have been misled by the doc string.  Or would
>> that have any downsides?
>
> That was my first thought when I noticed the problem, and came up with
> this patch to fix it:
>
> diff --git a/lisp/emacs-lisp/tabulated-list.el 
> b/lisp/emacs-lisp/tabulated-list.el
> index b13f609f88..d6bec72ade 100644
> --- a/lisp/emacs-lisp/tabulated-list.el
> +++ b/lisp/emacs-lisp/tabulated-list.el
> @@ -271,11 +271,12 @@ tabulated-list-init-header
>       (button-props `(help-echo "Click to sort by column"
>                       mouse-face header-line-highlight
>                       keymap ,tabulated-list-sort-button-map))
> +        (len (length tabulated-list-format))
>       (cols nil))
>      (if display-line-numbers
>          (setq x (+ x (tabulated-list-line-number-width))))
>      (push (propertize " " 'display `(space :align-to ,x)) cols)
> -    (dotimes (n (length tabulated-list-format))
> +    (dotimes (n len)
>        (let* ((col (aref tabulated-list-format n))
>            (label (nth 0 col))
>            (width (nth 1 col))
> @@ -293,7 +294,11 @@ tabulated-list-init-header
>          (apply 'propertize
>                 (concat label
>                         (cond
> -                        ((> (+ 2 (length label)) width) "")
> +                        ((and (> (+ 2 (length label)) width)
> +                                 (not (= (tabulated-list--column-number
> +                                          (car tabulated-list-sort-key))
> +                                         (1- len))))
> +                                 "")
>                          ((cdr tabulated-list-sort-key)
>                              (format " %c"
>                                      tabulated-list-gui-sort-indicator-desc))
>
> But after I saw that final (rightmost) column in the problematic cases
> was simply given too narrow a width, I thought it better to just change
> that and clarify the doc.  But maybe you're right that the misleading
> doc has affected third-party packages.

I note, though, that this patch, won't fix too narrow non-final columns,
as the Archive column in package-menu-mode, or the Status column in
process-menu-mode, etc.

Steve Berman