Bug#1117384: sxmo-utils: installs a global /usr/share/applications/mimeapps.list affecting nearly every desktop environment

Package: sxmo-utils
Severity: normal
X-Debbugs-Cc: [email protected]

While checking which desktop environments in Debian have a 
/usr/share/applications/${desktop}-mimeapps.list, I found that 
sxmo-utils installs a global /usr/share/applications/mimeapps.list.

This seems undesired for users of other desktop environments: it will 
change the default apps for *every* desktop environment or window 
manager that does not have its own desktop-specific mimeapps.list (for 
example Weston or LXQt), merely by being installed, even if SXMO is not 
the desktop environment that is currently in use.

Using this generic filename also means that SXMO will have a file 
conflict with any other package that tries to do the same thing: for 
example, if the Debian Desktop team wanted to install a basic 
/usr/share/applications/mimeapps.list in desktop-base to set Firefox ESR 
as the default web browser, they would be unable to do so without 
creating a file conflict. The generic filename is only intended to be 
used globally for defaults for an entire distribution (like 
desktop-base), and individual desktop environments should use their own 
desktop-specific filenames instead.

The intended way for desktop environments to set a preference for the 
apps that will be used is:

1. Set the XDG_CURRENT_DESKTOP environment variable to a desktop
   environment ID or a colon-separated sequence of desktop environment IDs.
   As I mentioned previously on #1050919, it wasn't clear to me whether
   sxmo-utils uses XDG_CURRENT_DESKTOP=SXMO or XDG_CURRENT_DESKTOP=sway,
   but if SMXO is indeed based on Sway, probably the best choice is
   XDG_CURRENT_DESKTOP="SXMO:sway".
2. Case-fold the chosen desktop environment ID to lower-case: "sxmo".
3. Create a mimeapps.list prefixed with that lower-case ID and a dash:
   "/usr/share/applications/sxmo-mimeapps.list".

For example GNOME, KDE Plasma and Cinnamon currently do this correctly 
in unstable, using desktop environment IDs "GNOME", "KDE" and 
"X-Cinnamon" respectively. Some other desktop environments "inherit" 
from those: for example Phosh and Budgie set 
XDG_CURRENT_DESKTOP="Phosh:GNOME" and 
XDG_CURRENT_DESKTOP="Budgie:GNOME", so they will inherit GNOME's default 
apps unless they define their own.

Please rename SXMO's /usr/share/applications/mimeapps.list to 
/usr/share/applications/sxmo-mimeapps.list or similar, and set 
XDG_CURRENT_DESKTOP during UI environment startup so that those 
defaults will be selected.

Thanks,
    smcv