5dplomacy/README.md

5D Diplomacy With Multiversal Time Travel

So you want to conquer Europe with a declarative build system

Let's start out by initializing the project. I always hate this part of projects; it's much easier to pick up something with an established codebase and ecosystem and figure out how to modify it to be slightly different than it is to strain genius from the empty space of possibility de novo. The ultimate goal of this project is summoning military aid from beyond space and time, though, so we're going to have to get used to it.

A nix flake init gives us a fairly useless flake template:

{
  description = "A very basic flake";

  outputs = { self, nixpkgs }: {

    packages.x86_64-linux.hello = nixpkgs.legacyPackages.x86_64-linux.hello;

    defaultPackage.x86_64-linux = self.packages.x86_64-linux.hello;

  };
}

We're going to replace every line in this file, but at least we got a start. Let's also git init and set that part up.

$ git init
$ git config --add user.name Jaculabilis
$ git config --add user.email jaculabilis@git.alogoulogoi.com
$ git add flake.nix README.md
$ git commit -m "Initial commit"
$ git remote add origin gitea@git.alogoulogoi.com:Jaculabilis/5dplomacy.git
$ git push -u origin master

We're doing this in .NET, so we need the .NET SDK. To do that, we're going to delcare a development environment in the flake config.

  inputs.flake-utils.url = "github:numtide/flake-utils";

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let pkgs = nixpkgs.legacyPackages.${system};
      in rec {
        devShell = pkgs.mkShell {
          packages = [ pkgs.dotnet-sdk ];
        };
      }
    );

Declaring inputs.flake-utils adds the flake-utils package as a dependency, which just gives us Nix helper functions. What's important here is that the packages.x86_64-linux.hello above has been abstracted away behind the eachDefaultSystem function: now we define our outputs with the system input as context, and flake-utils will define our outputs for each default system.

Basically, stripping the boilerplate, we're just doing this:

rec {
  devShell = pkgs.mkShell {
    packages = [ pkgs.dotnet-sdk ];
  };
}

pkgs.mkShell is the derivation builder that creates shell environments. It takes packages as a list of input packages that will be made available in the shell environment it creates. We add dotnet-sdk to this, commit the changes to git, and enter our new shell with nix develop:

$ which dotnet
/nix/store/87s452c8wj2zmy21q8q394f6rzf5y1br-dotnet-sdk-6.0.100/bin/dotnet