[Pkg-utopia-maintainers] Bug#1053446: xdg-email portal unavailable after default install

[Simon McVittie]

On Wed, 04 Oct 2023 at 10:57:18 +0200, Alec Leamas wrote:
> After a default install + installing flatpak the xdg-email portal does not
> work.

A default install of what exactly? What steps can be followed to reproduce
this problem?

The reason I ask is that Flatpak apps can't run the /usr/bin/xdg-email
from the host system, so if your steps to reproduce involve something
happening inside a Flatpak app that will run xdg-email from the PATH,
a dependency on xdg-utils on the host is not going to have the effect
that you're hoping for.

Inside a Flatpak app, none of the programs installed from .deb packages in
the host's /usr/bin are available. Instead, /usr comes from the Flatpak
runtime. If the app wants to be able to run xdg-email, then either the
app or its runtime needs to include the same code that is available
in Debian's flatpak-xdg-utils package (but, again, installed inside
the Flatpak app or runtime, not on the host system, so a dependency on
flatpak-xdg-utils on the host would not be helpful).

For example, the reference runtime org.freedesktop.Platform contains
a /usr/bin/xdg-email executable compiled from the same codebase as
Debian's flatpak-xdg-utils package (at least, version 22.08 does,
I haven't checked older or newer branches). This means that derived
runtimes like org.gnome.Platform//44 also contain that executable.

> Since the xdg-email portal requires xdg-utils

It does not. It requires any email client on the host system, either
installed from a .deb or a Flatpak app (or a Snap app or anything else
that participates in the freedesktop.org ecosystem), that registers
itself in a .desktop file as a freedesktop.org MIME-type handler for the
pseudo-MIME-type "x-scheme-handler/mailto". For example, thunderbird or
mutt would be suitable.

This is the same thing that xdg-utils requires in order to have the
xdg-email executable work, in any desktop environment that doesn't have
its own special code path in xdg-utils.

Steps to demonstrate this, starting from a virtual machine image produced
by autopkgtest-build-qemu, which has no graphical environment installed
and should be approximately equivalent to an installation from
debian-installer with no tasks enabled:

# apt install openbox xdm xorg flatpak mutt xterm
# apt purge xdg-utils
Package 'xdg-utils' is not installed, so not removed
# reboot
(GUI: log in to xdm, right-click on background, open a terminal)
$ flatpak remote-add --user --if-not-exists flathub flathub https://dl.flathub.org/repo/flathub.flatpakrepo
$ flatpak install --user flathub org.freedesktop.Platform//22.08
$ flatpak run org.freedesktop.Platform//22.08
[inside Flatpak app's shell]$ xdg-email nobody at example.com
(GUI: a new xterm opens, running mutt)

or for a more GUI reproducer, replace the last few steps with:

$ flatpak remote-add --user --if-not-exists flathub flathub https://dl.flathub.org/repo/flathub.flatpakrepo
$ flatpak install --user flathub com.belmoussaoui.ashpd.demo
$ flatpak run com.belmoussaoui.ashpd.demo
(GUI: go to Email tab, fill in Addresses: nobody at example.com, click Request)
(GUI: a new xterm opens, running mutt)

    smcv