Can't run X11 core18 snaps where core isn't installed

[Alan Pope 🍺🐧🐱 🦄]

Summary:

On a clean (no snaps) system. Install a core18 snap which needs X11, it won't launch until core snap is installed, which requires a manual step.

Steps to reproduce

1. Install a modern Linux distribution which does not ship any snaps out of the box. Tested with popOS 19.04 and Lubuntu 19.04.
2. snap install obs-studio
3. snap run obs-studio

Expected outcome

OBS launches.

Actual outcome

Error: unable to open display :0
/snap/obs-studio/391/usr/sbin:/snap/obs-studio/391/usr/bin:/snap/obs-studio/391/sbin:/snap/obs-studio/391/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
qt.qpa.screen: QXcbConnection: Could not connect to display :0
Could not connect to any X display.

Workaround

After installing the snap, install core (or some other snap which requires core)

snap install core

The snap then launches.

Seems core18 doesn't provide the interfaces expected by the application.

--------------------------------

Some data:-

alan@lubuntu1904:~$ which snap
/usr/bin/snap
alan@lubuntu1904:~$ snap version
snap 2.38+19.04
snapd 2.38+19.04
series 16
ubuntu 19.04
kernel 5.0.0-13-generic
alan@lubuntu1904:~$ snap list
No snaps are installed yet. Try 'snap install hello-world'.
alan@lubuntu1904:~$ snap install obs-studio
obs-studio 23.1.0 from Snapcrafters installed
alan@lubuntu1904:~$ snap list
Name Version Rev Tracking Publisher Notes
core18 20190409 941 stable canonical✓ base
obs-studio 23.1.0 391 stable snapcrafters -
alan@lubuntu1904:~$ snap changes
ID Status Spawn Ready Summary
1 Done today at 09:56 BST today at 09:56 BST Initialize system state
2 Done today at 10:01 BST today at 10:02 BST Install "obs-studio" snap
3 Done today at 10:01 BST today at 10:01 BST Initialise device