bug#67457: 29.1; Error when dragging mode line in terminal

[Jared Finder via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

On 2023-11-27 08:34, Eli Zaretskii wrote:
>> Date: Mon, 27 Nov 2023 07:16:34 -0800
>> From: Jared Finder <jared@finder.org>
>> Cc: stephen.berman@gmx.net, visuweshm@gmail.com, 67457@debbugs.gnu.org
>> 
>> >> 1. My original patch is likely inaccurate.  A better fix would be to
>> >> align the mouse-movement event with how it is emitted under GPM and
>> >> DOS.
>> >>   I will investigate.
>> >>
>> >> 2. Something broke with how GPM mouse mode is enabled between Emacs
>> >> 28.2
>> >> and HEAD.  I can help with a bisect here.
>> >
>> > Thanks, please do, on both counts.
>> 
>> Bisect identified the following commit as the bad commit, confirmed
>> locally:
>> 
>> jared@debian:^/emacs-devel$ git bisect bad
>> a28ede3a61a70cf83dfcba6c9d314fbb051a3a94 is the first bad commit
>> commit a28ede3a61a70cf83dfcba6c9d314fbb051a3a94
>> Author: Stefan Monnier <monnier@iro.umontreal.ca>
>> Date:
>> t-mouse.el: Make sure we apply the setting to new terminals
>> * lisp/t-mouse.el (gpm-mouse-tty-setup): New function.
>> (gpm-mouse-mode): Use it as well as 'tty-setup-hook".
>> * lisp/term/linux.el (terminal-init-linux): Remove gpm-specific code,
>> not neded any more.
>> lisp/t-mouse.el
>> lisp/term/linux.el | 2 --
> 
> Thanks, adding Stefan to the discussion.

Following up on #2:  The issue here is that after a28ede, 
gpm-mouse-tty-setup is never added to tty-setup-hook since it is only 
added within gpm-mouse-mode. This is clearly visible by checking the 
value of tty-setup-hook at startup, and after toggling gpm-mouse-mode 
off and on again.

The following simple patch fixes that, while leaving the details of how 
gpm-mouse-mode works an internal detail:

--- a/lisp/term/linux.el
+++ b/lisp/term/linux.el
@@ -13,6 +13,9 @@ terminal-init-linux
   ;; Compositions confuse cursor movement.
   (setq-default auto-composition-mode "linux")

+ ;; Ensure additional terminal setup is done when `gpm-mouse-mode' is 
enabled.
+ (ignore-errors (when gpm-mouse-mode (gpm-mouse-mode 1)))
+
   ;; Don't translate ESC TAB to backtab as directed by ncurses-6.3.
   (define-key input-decode-map "\e\t" nil)

One could also just revert just the linux.el changes in a28ede, though 
that assumes that gpm-mouse-enable exists.

   -- MJF