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

[Stephen Berman]

On Sun, 26 Nov 2023 16:24:46 -0800 Jared Finder <jared@finder.org> wrote:

> On 2023-11-26 14:08, Stephen Berman wrote:
>> On Sun, 26 Nov 2023 20:19:45 +0200 Eli Zaretskii <eliz@gnu.org> wrote:
>> 
>>>> From: Visuwesh <visuweshm@gmail.com>
>>>> Cc: Jared Finder <jared@finder.org>,  67457@debbugs.gnu.org
>>>> Date: Sun, 26 Nov 2023 23:39:45 +0530
>>>> [ஞாயிறு நவம்பர் 26, 2023] Eli Zaretskii wrote:
>>>>  >> Date: Sun, 26 Nov 2023 09:31:26 -0800
>>>> >> From:  Jared Finder via "Bug reports for GNU Emacs,
>>>> >>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>>>> >>
>>>> >> When in a terminal with the tab-line showing and mouse enabled, the
>>>> >> following error in shown when dragging the mode line down:
>>>> >>
>>>> >> <tab-line> <mouse-movement> is undefined
>>>> >
>>>> > Thanks, but I cannot reproduce this, at least not on MS-Windows (I
>>>> > don't have access to a Posix system with a mouse-capable text
>>>> > terminal).
>>>> I can reproduce this in xterm in master branch commit
>>>> 2fca889cfb4fa495a6ffa0c7fe368551ee9a32bc.
>>> Thanks.
>>> And the fix solves the problem?
>> I can also reproduce the problem on GNU/Linux with emacs-29 and master,
>> and the fix works for me.
>> 
>>> Does anyone have a Linux terminal with GPM mouse and can test there?
>> I do and after splitting the window and enabling gpm-mouse-mode I can't
>> drag the mode line with GPM mouse at all, whether global-tab-line is
>> enabled or not (on emacs-29 and master), and there are no errors or
>> other notifications in *Messages*.  Is dragging the mode line
>> supposed to work in the Linux terminal with GPM mouse?
>
> I also have a GPM mouse available and I see different behavior.
>
> On Emacs 28.2 (installed from Debian package): Dragging the mode line works
> fine, even if the tab line is visible. (GPM mouse mode is enabled by default)
>
> On HEAD (2407f8): Dragging the mode line does not work until I disable and
> re-enable GPM mouse mode. Then it works fine.

I can now confirm this (and see the same on the emacs-29 branch as on
master; I can't currently test emacs-28).  My previous report was
erroneous: I had never used (or even heard of) gpm-mouse-mode before
reading this bug thread, and didn't realize it was enabled by default,
so all I had done was to disable it; on re-enabling it, dragging works
as Jared reported, both without and with the tab line.

> This indicates two things to me:
>
> 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.

As noted, I see the same behavior on master and emacs-29, so it may be
quicker to use the latter for bisecting (I cannot help with that for the
time being, sorry).

Steve Berman