I have a workaround so this isn't exactly a problem for me. I'm just curious about what is going on, and what best practices are.
I'm setting up Arion. I think it will be helpful for my development flow in a project where I have several services that need to run and communicate with each other. Docker-compose is a nice way to handle this, but you have to have a Docker image to run, and it's a pain to create a new image after each code change. OTOH Arion will run an arbitrary command, and creates Nix-friendly images automatically. Very promising!
The Nix expression for the service I'm developing is exported from a flake, while the arion executable reads its configuration from a Nix expression that is not a flake. There is an example configuration that recommends importing a flake using builtins.getFlake which you can see here: https://github.com/hercules-ci/arion/blob/main/examples/flake/arion-pkgs.nix
The problem is that builtins.getFlake is slow. It adds >20s to every arion command I run. That includes starting services, reading logs, removing stopped containers, etc.
The example config includes a fallback that loads the flake using flake-compat instead of builtins.getFlake. When I use flake-compat loading the flake is nearly instant.
So I'm using flake-compat, and that seems to be working. (Many thanks to the flake-compat author!) But I'm curious why builtins.getFlake is so slow.