Auto-connection of gtk3-themes, icon-themes, and sound-themes interfaces

Today we have a process for content snap auto-connections, but this snap (perhaps understandably) doesn’t follow this convention.

Here are the relevant parts of the snap.yaml:

name: gtk-common-themes
...
slots:
  gtk3-themes:
    interface: content
    source:
      read:
      - $SNAP/share/themes/Adwaita
      - $SNAP/share/themes/Adwaita-dark
      - $SNAP/share/themes/HighContrast
      - $SNAP/share/themes/Ambiance
      - $SNAP/share/themes/Radiance
      - $SNAP/share/themes/EvoPop
      - $SNAP/share/themes/EvoPop-Azure
      - $SNAP/share/themes/Arc
      - $SNAP/share/themes/Arc-Dark
      - $SNAP/share/themes/Arc-Darker
      - $SNAP/share/themes/Communitheme
  icon-themes:
    interface: content
    source:
      read:
      - $SNAP/share/icons/Adwaita
      - $SNAP/share/icons/hicolor
      - $SNAP/share/icons/HighContrast
      - $SNAP/share/icons/Humanity
      - $SNAP/share/icons/Humanity-Dark
      - $SNAP/share/icons/ubuntu-mono-dark
      - $SNAP/share/icons/ubuntu-mono-light
      - $SNAP/share/icons/DMZ-Black
      - $SNAP/share/icons/DMZ-White
      - $SNAP/share/icons/Solus
      - $SNAP/share/icons/communitheme
      - $SNAP/share/icons/Suru
  sound-themes:
    interface: content
    source:
      read:
      - $SNAP/share/sounds/communitheme

@kenvandine - I think you have a bug in that all these things are in $SNAP/usr/share/… (you omit ‘usr’).

AFAICT, the exported files for themes, icons and sounds are all data files. There are css and xml files for the themes though. @kenvandine-- are these expected to work everywhere or do they require use of a particular core, base or other content (eg, gnome-3-28) snap?

@niemeyer - please weigh in on what you think this should look like.