bug#24963: 26.0.50; toggle-frame-maximized broken by double-buffering patch

[Stephen Berman]

On Fri, 18 Nov 2016 13:10:30 +0100 Stephen Berman <stephen.berman@gmx.net> 
wrote:

> 0. emacs -Q
> 1. M-x toggle-frame-maximized
>    => frame is maximized
> 2. M-x toggle-frame-maximized
>    => frame remains maximized, echo area displays "You can run the
>    command ‘toggle-frame-maximized’ with <M-f10>"
> 3. M-x toggle-frame-maximized
>    => now frame is restored to its prior size
>
> Git bisect says
>
> c29071587c64efb30792bd72248d3c791abd9337 is the first bad commit
> commit c29071587c64efb30792bd72248d3c791abd9337
> Author: Daniel Colascione <dancol@dancol.org>
> Date:   Thu Oct 20 20:34:36 2016 -0700
>
>     Add double-buffering support to reduce flicker
>
> Something in this patch seems to have affected modify-frame-parameters:
> in step 1 of the above recipe, the following code is executed (via
> set-frame-parameter): 
>
> (modify-frame-parameters nil (list (cons 'fullscreen 'maximized)))
>
> However, subsequently evaluating (frame-parameter nil 'fullscreen)
> returns nil, so that in step 2, the frame-parameter is (again) modified,
> though the frame is already maximized.  Now, however,  evaluating
> (frame-parameter nil 'fullscreen) returns `maximized', so in step 3, the
> frame is now demaximized.
>
> I executed modify-frame-parameters with a couple of other frame
> parameters, but didn't observe a similar problem.
>
> In GNU Emacs 26.0.50.5 (x86_64-suse-linux-gnu, GTK+ Version 3.14.15)
>  of 2016-11-16 built on rosalinde
> Repository revision: f63976857b4458bc7712e91d95c04fe2e2ca0106
> Windowing system distributor 'The X.Org Foundation', version 11.0.11601000
> System Description:   openSUSE 13.2 (Harlequin) (x86_64)

I just determined that the failure to demaximize in step 2 above only
happens when scroll-bar-mode is enabled.  I guess this is related to the
code added to src/gtkutil.c by the above patch to "[f]orce [GTK+] scroll
bars to be real X11 windows".

Steve Berman