Support building with flakes

[codygman]

It failed for me with:

✖1 ❯ sudo nix shell ".#nixosConfigurations.tower.config.system.build.toplevel" -c switch-to-configuration switch
warning: Git tree '/home/cody/devos2' is dirty
error: attribute 'currentSystem' missing

       at /nix/store/fk1pqfl3qv5r5jaf0lq1xzxnlzj13b2q-source/default.nix:1:12:

            1| { system ? builtins.currentSystem
             |            ^
            2| , profiling ? false
(use '--show-trace' to show detailed location information)

Maybe user error, or maybe changes need made for obelisk to work on flake-based systems?

[ikervagyok]

You could try adding --impure to your command line. It helped me with flakes, but I have no reflex/obelisk project using flakes (yet) to test this.

[chuahou]

Currently, when attempting to build command in pure evaluation mode, the first issue I encounter is

error: the path '~/.gitconfig' can not be resolved in pure mode

which is an issue with the combination of newer nixes and gitignore.nix. It's been fixed in the latter (see this PR), so patching dep/gitignore.nix/github.json gets around then.

The next issue I've encountered, which I've not found a way to work around, is the import <nixpkgs>s littered all around both obelisk and reflex-platform.

I will try using impure evaluation for now, but it would be nice to figure out a way to get pure evaluation to work in future.