Convert to flake

[avdv]

• add compatibility layer for nix-shell users
• update nixpkgs to nixos-22.05
• use flake.lock instead of nixpkgs.json

[tshaynik]

At the moment there are two separate flake.nix files, one in the project root and then a placeholder in core that would need to get synchronized to the same rev (presumeably these should always use the same nixpkgs commit?). So at the moment, to bump nixpkgs, you would have to run nix flake update in both the project root and in core to keep them in sync. Could it be useful to delete the core/flake.nix and make core/flake.lock a hard link? Then nix flake update in the project root would update core as well.

[avdv]

Yes, good point! I'll see if that works...

[tshaynik]

This looks good to me! (I'm still very new to Tweag and to Bazel, so somebody else should probably look it over as well)
Things I like about your approach:

• using nix-compat to not breaking the traditional workflow
• ability to use a single invocation of nix flake tool to manage pinning nixpkgs
• actual use of this ruleset within Bazel does not depend on any experimental flake features

[avdv]

This looks good to me! (I'm still very new to Tweag and to Bazel, so somebody else should probably look it over as well)

Thank you for the review! Another pair of eyes would have been good, but I accidentally already pushed this onto master... If somebody has any objections to this, let's just fix it in another PR.

Things I like about your approach:

* using nix-compat to not breaking the traditional workflow

* ability to use a single invocation of `nix flake` tool to manage pinning nixpkgs

* actual use of this ruleset within Bazel does not depend on any experimental flake features

👍 we might switch to nix flake usage in the future, when flakes are no longer considered experimental.

[aherrmann]

I can only echo @tshaynik's comments, looks good, thank you!