bug#37174: 26.2; Stabilize tabulated-list reversed sort

[Johan Claesson]

Hi,

Sorting with S multiple times in a tabulated-list buffer should be
stable but will sometimes reorder entries with the same value.  When the
sort order is reversed the function tabulated-list--get-sorter will
transform the sort function to sort the other way around by negating.  I
think this is what cause the needless reordering and that it should be
changed something like the following:

diff --git a/lisp/emacs-lisp/tabulated-list.el 
b/lisp/emacs-lisp/tabulated-list.el
index 63ae1f8c07..f30e2c0ec8 100644
--- a/lisp/emacs-lisp/tabulated-list.el
+++ b/lisp/emacs-lisp/tabulated-list.el
@@ -373,7 +373,7 @@ tabulated-list--get-sorter
                                   (if (stringp b) b (car b)))))))
       ;; Reversed order.
       (if (cdr tabulated-list-sort-key)
-          (lambda (a b) (not (funcall sorter a b)))
+          (lambda (a b) (funcall sorter b a))
         sorter))))
 
 (defsubst tabulated-list--col-local-max-widths (col)



Recipe for 26.2 or 27.0 (42f8fa8070):

emacs -Q a.el b.el

C-x C-b (pop buffer list buffer)

Goto buffer list buffer and put point in "Mode" column.

Press S to sort on Mode.  b.el is now before a.el in the list.

Press S twice more.  a.el is now before b.el.

Regards,

/Johan






In GNU Emacs 26.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.4)
 of 2019-04-22 built on goblin
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description:     Ubuntu 19.04

Recent messages:
((1 . b) (1 . a) (2 . b) (2 . a))
0.001_013s ((1 . b) (1 . a) (2 . b) (2 . a))
Saving file /ssd/home/jcl/share/elisp/picpocket.el...
Wrote /ssd/home/jcl/share/elisp/picpocket.el
Saving file /ssd/home/jcl/share/elisp/jcl-bugfix.el...
Wrote /ssd/home/jcl/share/elisp/jcl-bugfix.el
Quit
Saving file /ssd/home/jcl/build/emacs/lisp/emacs-lisp/tabulated-list.el...
Wrote /ssd/home/jcl/build/emacs/lisp/emacs-lisp/tabulated-list.el
C-2 C-g is undefined

Configured using:
 'configure --prefix=/ssd/home/jcl/usr --with-x-toolkit=gtk3
 --with-xwidgets --without-compress-install --with-modules
 PKG_CONFIG_PATH=/home/jcl/usr/lib/pkgconfig'

Configured features:
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NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
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LIBSYSTEMD LCMS2

Important settings:
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Major mode: Emacs-Lisp

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  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  temp-buffer-resize-mode: t
  line-number-mode: t
  transient-mark-mode: t
  abbrev-mode: t

Load-path shadows:
/home/jcl/elpa/soap-client-3.1.5/soap-inspect hides 
/ssd/home/jcl/build/emacs-26.2/lisp/net/soap-inspect
/home/jcl/elpa/soap-client-3.1.5/soap-client hides 
/ssd/home/jcl/build/emacs-26.2/lisp/net/soap-client
/home/jcl/elpa/let-alist-1.0.6/let-alist hides 
/ssd/home/jcl/build/emacs-26.2/lisp/emacs-lisp/let-alist

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