bug#41251: 28.0.50; Cannot customize mouse-drag-and-drop-region modifier

[David Ponce]

Hello,

There is an issue in the definition of `mouse-drag-and-drop-region' that
will not correctly set the option depending on selected modifier. That
is, when any option "Enable, but copy with the MODIFIER modifier" is
set, the value of `mouse-drag-and-drop-region' is always set to the
symbol 'modifier instead of 'alt, 'super, 'hyper, 'shift, 'control, or
'meta, depending on the selected option. It seems due to a missing comma
in the backquote expression.

The below patch fixed the issue for me:

diff --git a/installs/emacs/lisp/mouse.el b/emacs.d/mouse.el
index 9703d95..795b4da 100644
--- a/installs/emacs/lisp/mouse.el
+++ b/emacs.d/mouse.el
@@ -2556,7 +2556,7 @@ region, text is copied instead of being cut."
              (lambda (modifier)
                `(const :tag ,(format "Enable, but copy with the %s modifier"
                                      modifier)
-                       modifier))
+                       ,modifier))
              '(alt super hyper shift control meta))
           (other :tag "Enable dragging the region" t))
   :version "26.1")

Thanks!

In GNU Emacs 28.0.50 (build 8, x86_64-pc-linux-gnu, GTK+ Version 3.24.13, cairo 
version 1.16.0)
 of 2020-05-12 built on kilauea
Repository revision: 4645430b9287c3f5ae9863d465a5dd4158e313a9
Repository branch: master
Windowing system distributor 'Fedora Project', version 11.0.12006000
System Description: Fedora 31 (KDE Plasma)