bug#45361: 28.0.50; tabulated-list-mode: should be sorting by specified sort function

[Stephen Berman]

On Tue, 22 Dec 2020 08:13:50 +0100 Jean Louis <bugs@gnu.support> wrote:

> PROBLEM:
>
> The variable `tabulated-list-format' provides for programmer
> option to sort columns and I would like to sort number as
> strings "12" as numbers, not as strings. I do not know how to
> properly provide the sorting function to `tabulated-list-format' so
> that it works when actually sorting.
[...]
> Then I would like to use the function `string-collate-lessp' as that
> seem to understand how numbers should be compared.
>
> For example this is giving me correct result:
>
> (sort '("121" "117" "1") 'string-collate-lessp) => ("1" "117" "121")

But:

(sort '("21" "117" "1") 'string-collate-lessp) => ("1" "117" "21")

So string-collate-lessp doesn't do what it seems you want.

[...]
> But when I click on "Count" column or press S then it again gets
> sorted rather alphabetic, not by using my function.
>
> That is where I would need help to understand what is happening.
>
> Because when I press S in the column "Count" when cursor is on the number, it 
> invokes this function:
>
> (defun tabulated-list-sort (&optional n)
>   "Sort Tabulated List entries by the column at point.
> With a numeric prefix argument N, sort the Nth column."
>   (interactive "P")
>   (let ((name (if n
>                 (car (aref tabulated-list-format n))
>               (get-text-property (point)
>                                  'tabulated-list-column-name))))
>     (if (nth 2 (assoc name (append tabulated-list-format nil)))
>         (tabulated-list--sort-by-column-name name)
>       (user-error "Cannot sort by %s" name))))
>
> Then this one:
>
> (defun tabulated-list--sort-by-column-name (name)
>   (when (and name (derived-mode-p 'tabulated-list-mode))
>     ;; Flip the sort order on a second click.
>     (if (equal name (car tabulated-list-sort-key))
>       (setcdr tabulated-list-sort-key
>               (not (cdr tabulated-list-sort-key)))
>       (setq tabulated-list-sort-key (cons name nil)))
>     (tabulated-list-init-header)
>     (tabulated-list-print t)))
>
> And if I read well those functions do not search for my function and
> invoke `my-sort', but they should. Am I right there?

Actually, tabulated-list-print does call my-sort via
tabulated-list--get-sorter.  Anyway, buffer-menu.el has the function
`tabulated-list-entry-size->', which with a small adjustment does what
you seem to want.  Try this:

(defun my-tabulated-list-entry-size-> (entry1 entry2)
  (> (string-to-number (aref (cadr entry1) 0))
     (string-to-number (aref (cadr entry2) 0))))

(let ((buffer "*tabulated*"))
  (switch-to-buffer-other-window buffer)
  (setq tabulated-list-format
        [("Count" 10 my-tabulated-list-entry-size-> :right-align t)
         ("Name" 60 t)])
  (setq tabulated-list-entries '((6 ["6" "Mercury"])
                                 (7 ["7" "GNU Emacs"])
                                 (8 ["8" "YouTube Videos"])
                                 (9 ["9" "Speedy worker cleaning tables in a 
restaurant"])
                                 (71 ["71" "Trenching"])
                                 (82 ["82" "Easier trenching idea"])))
  (tabulated-list-mode)
  (tabulated-list-init-header)
  (hl-line-mode)
  (tabulated-list-print))

Steve Berman