apparently the 7.1.x series is now old enough that even though it
does still get security fixes, the mattermost team no longer mentions
this on their blog, so we missed out on a couple. fun!
this replaces niv with nix flakes, attempting to preserve the old
structure as much as possible. Notable caveats:
- I'm not sure if flake inputs expose version information anywhere, so
the version in pkgs/mattermost/default.nix is now hardcoded.
Confusingly, this appears to trigger a rebuild. Maybe I've missed something.
- a lot of the old-style host.nix & deploy.nix machinery in nix-hexchen
does not work with flakes, and their newer replacements are not exposed
by upstream; I've put basic imitations of the relevant parts in this repo
- (in particular, directories in hosts/ won't become deployable configs
automatically)
- parts of the code are now probably more complicated than they'd have to be
- old variables names were preserved; confusingly, this means the flake
inputs are still called "sources"
