Use meaningful name for image file about nixos-generators

[zimbatm]

Injecting that type of metadata into the output means that it will be rebuilt on every nixpkgs commit, even if the result doesn't change. The output is quite large so it's probably desirable to avoid unnecessary churn.

I think a better approach would be to keep a cache of commit IDs to derivation hashes outside of nix

[davidak]

Injecting that type of metadata into the output means that it will be rebuilt on every nixpkgs commit, even if the result doesn't change. The output is quite large so it's probably desirable to avoid unnecessary churn.

OK, yes. So is that a problem on the official image too?

I think a better approach would be to keep a cache of commit IDs to derivation hashes outside of nix

Would you implement that into nixos-generators or should i just copy and rename the file after build?

[zimbatm]

I could be wrong but I think that NixOS reduces the churn by only pushing the image once in a while instead of at each channel release.

It would be best to find a generic solution. It's the same issue with the dockerTools.buildImage outputs as well. But having one built in nixos-generators is also acceptable.