Bug#1117444: Cannot run: TypeError by GioUnix.DesktopAppInfo.get_filename() in gtweak/utils.py

[Simon McVittie]

Control: reassign -1 python3-gi 3.50.0-7
Control: retitle -1 pygobject: GioUnix.DesktopAppInfo requires extraneous parameter to get_filename() when using GLib 2.84.x
Control: affects -1 + gnome-tweaks

Here is a minimal reproducer for the bug. You need python3-gi and at 
least one .desktop file: "apt install python3-gi xterm" is sufficient.

> $ python3
> >>> from gi.repository import Gio
> >>> Gio.app_info_get_all()[0].get_filename()

This works fine with GLib 2.86 from experimental: it tells me the 
filename of one of my .desktop files. However, the same fails with GLib 
2.84 from testing/unstable:

> $ python3
> >>> from gi.repository import Gio
> >>> Gio.app_info_get_all()[0].get_filename()
> Traceback (most recent call last):
>   File "<python-input-2>", line 1, in <module>
>     Gio.app_info_get_all()[0].get_filename()
>     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
> TypeError: GioUnix.DesktopAppInfo.get_filename() takes exactly 1 argument (0 given)

I think this is a regression in pygobject caused by the patches that 
were added to make it forward-compatible with GLib 2.86. Unfortunately 
it seems that at least one of those changes is not fully 
backward-compatible with GLib 2.84.

One way to resolve this would be if the release team give the go-ahead 
to do the GLib 2.86 transition; the other way would be to revert or 
improve the pygobject changes (and if they are reverted for now, reapply 
them as part of the GLib 2.86 transition).

I am confident that the proposed patch to gnome-tweaks is *not* a valid 
solution, because it would introduce the opposite regression when used 
with both the new pygobject and the new GLib:

> $ python3
> >>> from gi.repository import Gio
> >>> app = Gio.app_info_get_all()[0]
> >>> app.get_filename()
> '/usr/share/applications/io.github.fabiangreffrath.Hexen.desktop'
> >>> app.get_filename(app)
> Traceback (most recent call last):
>   File "<python-input-3>", line 1, in <module>
>     app.get_filename(app)
>     ~~~~~~~~~~~~~~~~^^^^^
> TypeError: GioUnix.DesktopAppInfo.get_filename() takes exactly 1 argument (2 given)

Instead, I think this needs to be fixed in pygobject.

     smcv