bug#50194: 28.0.50; tabulated-list-print (with non-nil UPDATE argument) doesn't clean up excess entries

bug#50194: 28.0.50; tabulated-list-print (with non-nil UPDATE argument) doesn't clean up excess entries

[Shitikanth]

(tabulated-list-print nil t) does not seem to clean up excess remaining
entries/lines if the number of tabulated-list-entries has decreased.

Demo:
    (defun demo-generate-entries (n)
        (mapcar (lambda (i)
                  (list i (vector (format "title %s" i))))
                (number-sequence 1 n)))

    (let ((buf (get-buffer-create "*demo*")))
      (with-current-buffer buf
        (tabulated-list-mode)
        (setq tabulated-list-format '[("title" 70 t)])
        (setq tabulated-list-sort-key '("title"))
        (setq tabulated-list-entries (demo-generate-entries 8))
        (tabulated-list-print)
        (pop-to-buffer buf)
        (setq tabulated-list-entries (demo-generate-entries 4))
        (tabulated-list-print nil t)
        ))

Expected behaviour:
At the end, *demo* buffer should show only 4 entries.

Observed behaviour:
*demo* buffer still holds 8 entries, still showing 4 entries that are
now removed from tabulated-list-entries.

bug#50194: 28.0.50; tabulated-list-print (with non-nil UPDATE argument) doesn't clean up excess entries

[Shitikanth]

[-- Attachment #1: Type: text/plain, Size: 1112 bytes --]

Proposed fix.

On Wed, 25 Aug 2021 at 00:26, Shitikanth <shitikanth1@gmail.com> wrote:
>
> (tabulated-list-print nil t) does not seem to clean up excess remaining
> entries/lines if the number of tabulated-list-entries has decreased.
>
> Demo:
>     (defun demo-generate-entries (n)
>         (mapcar (lambda (i)
>                   (list i (vector (format "title %s" i))))
>                 (number-sequence 1 n)))
>
>     (let ((buf (get-buffer-create "*demo*")))
>       (with-current-buffer buf
>         (tabulated-list-mode)
>         (setq tabulated-list-format '[("title" 70 t)])
>         (setq tabulated-list-sort-key '("title"))
>         (setq tabulated-list-entries (demo-generate-entries 8))
>         (tabulated-list-print)
>         (pop-to-buffer buf)
>         (setq tabulated-list-entries (demo-generate-entries 4))
>         (tabulated-list-print nil t)
>         ))
>
> Expected behaviour:
> At the end, *demo* buffer should show only 4 entries.
>
> Observed behaviour:
> *demo* buffer still holds 8 entries, still showing 4 entries that are
> now removed from tabulated-list-entries.
>
>
>

[-- Attachment #2: 0001-tabulated-list-print-delete-excess-lines-bug-50194.patch --]
[-- Type: application/octet-stream, Size: 857 bytes --]

From 3a910de8512c125810f8681b1bcae41fa3135318 Mon Sep 17 00:00:00 2001
From: Shitikanth Kashyap <shitikanth1@gmail.com>
Date: Wed, 25 Aug 2021 00:33:55 +0530
Subject: [PATCH] tabulated-list-print delete excess lines (bug#50194)

---
 lisp/emacs-lisp/tabulated-list.el | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lisp/emacs-lisp/tabulated-list.el b/lisp/emacs-lisp/tabulated-list.el
index f0ee78745a..fecfa91147 100644
--- a/lisp/emacs-lisp/tabulated-list.el
+++ b/lisp/emacs-lisp/tabulated-list.el
@@ -481,6 +481,8 @@ tabulated-list-print
               (forward-line 1)
               (delete-region old (point))))))
       (setq entries (cdr entries)))
+    (when update
+      (delete-region (point) (point-max)))
     (set-buffer-modified-p nil)
     ;; If REMEMBER-POS was specified, move to the "old" location.
     (if saved-pt
-- 
2.25.1

bug#50194: 28.0.50; tabulated-list-print (with non-nil UPDATE argument) doesn't clean up excess entries

[Lars Ingebrigtsen]

Shitikanth <shitikanth1@gmail.com> writes:

> Proposed fix.

Makes sense to me; applied to Emacs 28.

This change was small enough to apply without assigning copyright to the
FSF, but for future patches you want to submit, it might make sense to
get the paperwork started now, so that subsequent patches can be applied
speedily. Would you be willing to sign such paperwork?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no