Trigger font cache rebuild if new fonts added to the system

[Igor Ljubuncic]

This is a placeholder bug for the implementation of font cache rebuild if new fonts are added to the system (global or per-user) after a snap is installed to ensure font consistency.

[Sergio Schvezov (sergiusens)]

The only way I can think of this working is if snapd executes the configure hook for snaps using the desktop-y interfaces.

[Igor Ljubuncic (igorljubuncic-deactivatedaccount)]

A potential solution could be that any snap run * commands checks for the mtime for the system font caches directory, and if these have not been updated by any other utility and/or fontconfig, then snapd can trigger the system font cache refresh.

The mtime check could work around any snap that doesn't use desktop launchers, where there is no check for new fonts after snaps are installed, or there's no hook/notification on font addition.

This also works around any time consistency whereby snapd periodically checks and updates fonts - but a snap is run in the window between the two and after new fonts were added.