Bug#1115732: gnome-session-common: [49.x] Debian customizations to default apps were lost

[Simon McVittie]

Package: gnome-session-common
Version: 49.0-1
Severity: serious
Tags: experimental

After upgrading gnome-session (and gnome-shell and gdm) to 49.x, my 
system's default web browser changes from Firefox ESR to GNOME Web 
(Epiphany). This seems like something we should resolve before 
re-uploading gnome-session-common to unstable, at least for Firefox.

Upstream, gnome-mimeapps.list is generated as a side effect of the "GNOME 
OS" images, using the MIME types for which they advertise support - 
which we can't do in Debian, because having Build-Depends on every GNOME 
app would be fragile, but we can certainly regenerate the file 
periodically and commit the result. I don't think there is a DFSG 
problem here - the file is in a form that is entirely reasonable to 
edit, even if not really intended to be edited.

A simplistic way to do this would be to patch data/gnome-mimeapps.list, 
ignoring the comment about how it isn't intended to be edited directly; 
or we could stop installing upstream's data/gnome-mimeapps.list and 
bring back our Debian-specific version.

A way that might scale better would be to use 
<https://gitlab.gnome.org/heftig/gnome-mimeapps/> or maybe
<https://gitlab.gnome.org/GNOME/gnome-build-meta/-/tree/master/files/gnome-mimeapps>, 
either of which would have to be run in a container that has all the
relevant apps installed (or at least their .desktop files).

Or, since the only thing that 
https://gitlab.gnome.org/heftig/gnome-mimeapps/ reads from the .desktop 
files seems to be their MimeType list, perhaps we could adapt that 
program to read that information from AppStream metadata? For example 
/var/lib/app-info/yaml/deb.debian.org_debian_dists_forky_main_dep11_Components-amd64.yml.gz 
has entries like:

---
Type: desktop-application
ID: firefox-esr.desktop
...
Launchable:
  desktop-id:
  - firefox-esr.desktop
Provides:
  mediatypes:
  - text/html
  ...

and

---
Type: desktop-application
ID: org.gnome.Showtime
...
Launchable:
  desktop-id:
  - org.gnome.Showtime.desktop
...
Provides:
  mediatypes:
  - video/3gp
  - video/3gpp
  ...

which looks like all the information we need?

    smcv