add a nix flake

[TroyKomodo]

Not sure if wanted, can close if not.

Adds nix flake so that nix shells can inherit the required tooling to build / develop the project.

developer env usage

# direnv + nix
direnv allow

# nix only
nix develop .

package building

The nix flake also adds the package building process used by end users (separate component can be removed).

nix build .#sccache

module integration

# Add flake input
sccache.url = "github:mozilla/sccache";

# Add overlay
nixpkgs.overlays = [ sccache.overlays.default ];
environment.systemPackages = [ pkgs.sccache ]; # nixos

[nbp]

I am not familiar with the .envrc files, and I am not fond of pulling online resources when doing local development. However this file might be slightly outdated (3.0.7 -> 3.1.0) compared to https://github.com/nix-community/nix-direnv/blob/master/templates/flake/.envrc

Overall the flake looks good.

I would not have included the NixOS / HomeManager modules only for registering the flake output as part of the system packages, unless there was some added value such as registering a systemd jobs for starting the sccache server.

I will also note that the lack of overlay for the definition of packages imply that this flake creates an additional instances of Nixpkgs (line 54: import nixpkgs) when using any of the modules, which is a bad practice.

On another note, I am surprise that rustup now works in nix develop shells, but I guess things sometimes get fixed by not looking at them for about 10 years.

[TroyKomodo]

I am not familiar with the .envrc files, and I am not fond of pulling online resources when doing local development. However this file might be slightly outdated (3.0.7 -> 3.1.0) compared to https://github.com/nix-community/nix-direnv/blob/master/templates/flake/.envrc

direnv basically initializes the shell when entering the directory. Also plays nice with vscode using the https://marketplace.visualstudio.com/items?itemName=mkhl.direnv extension which causes all of the other vscode extensions to inherit the nix dev shell. (such as rust-analyzer)

Hmm, i see the latest release is https://github.com/nix-community/nix-direnv/releases/tag/3.0.7, but i see the 3.1.0 tag so i think they just forgot to create a git release for it. I'll update.

I would not have included the NixOS / HomeManager modules only for registering the flake output as part of the system packages, unless there was some added value such as registering a systemd jobs for starting the sccache server.

I think thats out of scope for this. I'll remove them.

I will also note that the lack of overlay for the definition of packages imply that this flake creates an additional instances of Nixpkgs (line 54: import nixpkgs) when using any of the modules, which is a bad practice.

I think I fixed it?

[nbp]

This sounds good to me!

I could be pedantic about the differences between final and prev for pulling library functions, but this has no impact today …

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.04%. Comparing base (cd7dcd5) to head (3c5e3c7).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2518   +/-   ##
=======================================
  Coverage   71.04%   71.04%           
=======================================
  Files          64       64           
  Lines       35369    35369           
=======================================
+ Hits        25128    25129    +1     
+ Misses      10241    10240    -1     

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