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

[Jean Louis <bugs@gnu.support>]

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.

DATA:

The tabulated list mode works as this:

(let ((buffer "*tabulated*"))
  (switch-to-buffer-other-window buffer)
  (setq tabulated-list-format [("Count" 10 t :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))

When evaluated I would get the list such as:

         6 Mercury
         7 GNU Emacs
        71 Trenching
         8 YouTube Videos
        82 Easier trenching idea
         9 Speedy worker cleaning tables in a restaurant

and my goal would be to be able to sort the column "Count" so
that I get a result sorted by the number (which is string):

         6 Mercury
         7 GNU Emacs
         8 YouTube Videos
         9 Speedy worker cleaning tables in a restaurant
        71 Trenching
        82 Easier trenching idea


The description of `tabulated-list-format' says:

The format of the current Tabulated List mode buffer.
This should be a vector of elements (NAME WIDTH SORT . PROPS),
where:
 - NAME is a string describing the column.
   This is the label for the column in the header line.
   Different columns must have non-‘equal’ names.
 - WIDTH is the width to reserve for the column.
   For the final element, its numerical value is ignored.
 - SORT specifies how to sort entries by this column.
   If nil, this column cannot be used for sorting.
   If t, sort by comparing the string value printed in the column.
   Otherwise, it should be a predicate function suitable for
   ‘sort’, accepting arguments with the same form as the elements
   of ‘tabulated-list-entries’.

I could make a function to list what elements are accepted on click:

(defun my-sort (&rest args)
  (message "%s" args))

and include it here:

(let ((buffer "*tabulated*"))
  (switch-to-buffer-other-window buffer)
  (setq tabulated-list-format [("Count" 10 my-sort :right-align t) ("Name" 60 t)])
  (setq tabulated-list-entries '((1 ["6" "Mercury"])
				 (2 ["7" "GNU Emacs"])
				 (3 ["8" "YouTube Videos"])
				 (4 ["9" "Speedy worker cleaning tables in a restaurant"])
				 (5 ["71" "Trenching"])
				 (6 ["82" "Easier trenching idea"])))
  (tabulated-list-mode)
  (tabulated-list-init-header)
  (hl-line-mode)
  (tabulated-list-print))

Then I can see something like this in `*Messages*' buffer:

((6 [82 Easier trenching idea]) (5 [71 Trenching]))
((6 [82 Easier trenching idea]) (4 [9 Speedy worker cleaning tables in a restaurant]))
((5 [71 Trenching]) (4 [9 Speedy worker cleaning tables in a restaurant]))
((3 [8 YouTube Videos]) (2 [7 GNU Emacs]))
((3 [8 YouTube Videos]) (1 [6 Mercury]))
((2 [7 GNU Emacs]) (1 [6 Mercury]))
((6 [82 Easier trenching idea]) (3 [8 YouTube Videos]))
((5 [71 Trenching]) (3 [8 YouTube Videos]))
((4 [9 Speedy worker cleaning tables in a restaurant]) (3 [8 YouTube Videos]))

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")

Then I am attempting to make the sorting function:

(defun my-sort (s1 s2)
  (let* ((s1-number (elt (cadr s1) 0))
	 (s2-number (elt (cadr s2) 0)))
    (string-collate-lessp s1-number s2-number)))

(my-sort '(2 ["7" "GNU Emacs"]) '(1 ["6" "Mercury"]))

Now this works well first time as when the list is displayed it is
already sorted by "Count":

(let ((buffer "*tabulated*"))
  (switch-to-buffer-other-window buffer)
  (setq tabulated-list-format [("Count" 10 my-sort :right-align t) ("Name" 60 nil)])
  (setq tabulated-list-entries '((1 ["6" "Mercury"])
				 (2 ["7" "GNU Emacs"])
				 (3 ["8" "YouTube Videos"])
				 (4 ["9" "Speedy worker cleaning tables in a restaurant"])
				 (5 ["71" "Trenching"])
				 (6 ["82" "Easier trenching idea"])))
  (tabulated-list-mode)
  (tabulated-list-init-header)
  (hl-line-mode)
  (tabulated-list-print))

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?

Jean



In GNU Emacs 28.0.50 (build 2, x86_64-pc-linux-gnu, X toolkit, cairo version 1.14.8, Xaw3d scroll bars)
 of 2020-11-25 built on protected.rcdrun.com
Repository revision: 30c437752df0a3a9410f1249fa0f237110811af2
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.11907000
System Description: Hyperbola GNU/Linux-libre

Configured using:
 'configure --prefix=/package/text/emacs --with-modules
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Important settings:
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-- 
Thanks,
Jean Louis
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