Bug#964846: reportbug-gtk: mua xdg-email: does not work with the GTK UI

Dear GTK/GNOME list,

I'm looking for help with a problem in the reportbug GTK ui (bug
#964846). The GTK ui has code that uses VTE to run certain commands in a
terminal. These commands include package-specific bug scripts and
user-selected external MUAs used for bug submission. The problem is that
MUA invocation often fails if xdg-email is used.

Since the MUA selection is a user choice, the current code does not know
in advance whether the MUA needs a terminal or not, and therefore always
spawns the terminal to launch the MUA. This works fine for most MUAs,
but does not work reliably when trying to use xdg-email to launch the
user's preferred MUA. See below for the observations so far.

Is there a simple way to change the terminal-based command invocation in
reportbug's GTK ui in a way that will work reliably with xdg-email? What
changes are needed?  (Would a change from Vte.terminal.spawn_sync to
Vte.terminal.spawn_async make a difference? What exactly needs to be
changed for this?)

Or is it fine to stick with spawn_sync and we should instead try harder
to only use terminal-based command invocation if a terminal is really
needed? (That is probably a good idea anyway, but does not provide an
explanation of why the current code is failing.)

The code is here:
https://salsa.debian.org/reportbug-team/reportbug/-/blob/master/reportbug/ui/gtk_ui.py#L1467

On 11/07/2020 11:34, Paul Wise wrote:
> If I add some debugging to the SystemPage execute function from the
> gtk_ui.py file to print the xdg-email command that is run under a VTE
> terminal. I then copied the command into a GNOME Terminal and it ran
> there just fine. I then commented out the self.terminal.spawn_sync call
> and the black screen in the reportbug UI stayed around instead of
> closing immediately. Then I tested subprocess.run() instead of Vte
> spawn_sync and it worked. Then I tested the mutt reportbug option and
> it worked fine. Then I tested setting the reportbug mua option to the
> evolution MUA (which xdg-email opens normally) and it worked fine. Then
> I hacked the code to append "; sleep inf" to the command being run and
> xdg-email worked fine. Then I tried "; sleep 0.1s" and it did not work.
> 0.5s does not work but 0.9s does work. So I think there is some sort of
> race condition within VTE or something.

So I added the sleep hack (set to 3s) and tried "mua xdg-email" in a few
variants:

Desktop   preferred MUA   Result
Gnome      evolution     compose window opened, then closed within 3s
Gnome     thunderbird    compose window opened, no problem
Gnome     claws-mail     compose window opened, then closed within 3s

Then I commented out the special casing of thunderbird in the gnome3
part of xdg-email, and thunderbird starting showing the same problem:
the compose window was killed within 3 seconds.

Then I tried to reproduce in Xfce (on stable, not sid):
Xfce      evolution     compose window opened, then closed within 3s
Xfce     thunderbird    does not work due to #964799
Xfce      sylpheed      compose window opened, then closed within 3s

After fixing #964799, the problem also shows with thunderbird.


> BTW, while debugging I saw this deprecation warning:
>
> <stdin>:1: DeprecationWarning: Vte.Terminal.spawn_sync is deprecated
> https://developer.gnome.org/vte/unstable/VteTerminal.html#vte-terminal-spawn-sync