Comment 0 for bug 1803534

Fontconfig 2.13.0 changed the cache file naming scheme to be based on the contents of ".uuid" file in the directory rather than a hash of the directory name. On a pure debs system this doesn't really matter since everything is using the same libfontconfig.so.

When snaps are involved, it can lead to some apps not seeing the cache files produced by a different fontconfig version. In particular, while libfontconfig 2.13 can reuse 2.12's cache files for read only directories, the reverse is not true. This will be a problem for apps built on top of the "core18" base snap when run on later Ubuntu releases (cosmic, disco, etc).

By providing a backport of the UUID cache file feature to bionic for use by snap applications, we'd avoid this. Having it in bionic-updates would be ideal so that snapcraft picks it up automatically.