Nixify

[knedlsepp]

This adds a development environment using the nix package manager.
It's somewhat of an alternative to the current Dockerfile, but has more
powerful caching and reproducibility guarantees.
Also I included an integration test that:

• Builds libdragon
• Builds the examples
• Starts a virtual machine
• Runs the audioplayer.z64 example ROM in ares
• Uses OCR to wait for the "Module Audio Player" to appear on screen
• Takes a screenshot for later inspection.

It can be run using nix build .#checks.x86_64-linux.vmTest.
There's lots more neat things that can be done with nix.
I'm putting this out as a draft mostly for visibility.

[bates64]

I've had success using a custom crossSystem and then using pkgs.mkShell to get the toolchain. Example

let
    crossSystem = {
        config = "mips64-elf";
        system = "mips64-elf";
        gcc.arch = "vr4300";
        gcc.tune = "vr4300";
        gcc.abi = "32";
    };
    pkgsCross = import nixpkgs { inherit system, crossSystem; };
in
    devShells.default = pkgsCross.mkShell {
        # ...
    }

Using NixOS's mips64-embedded might work, but it's not tuned to the vr4300, and I don't believe it's built on Hydra anyway. I've been using a Cachix cache so users don't have to build from source: https://papermario-dx.cachix.org

[knedlsepp]

I've had success using a custom crossSystem

Neat! Thanks for sharing! 😊