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Using Derivations ​

mkShell ​

Use this attribute(function?) to compose reproducible development shells via the devShells attribute. As discussed in Using Nix Flakes, it is particularly handy when used in combination with direnv.

inputsFrom ​

Takes the outputs from another derivation within the Flake (typically a package derivation), and integrates them into the current derivation. This is a good way to abide by the DRY principle.

For example, the mkShell derivation below will have cmake, gcc12, and pkg-config in its environment.

nix
devShells.default = pkgs.mkShell {
  inputsFrom = [self.packages.${system}.default ];
};

packages.default = pkgs.stdenv.mkDerivation {
  name = "your-package";
  src = ./.;
  buildInputs = with pkgs; [
    cmake
    gcc12
    pkg-config
  ];
};
devShells.default = pkgs.mkShell {
  inputsFrom = [self.packages.${system}.default ];
};

packages.default = pkgs.stdenv.mkDerivation {
  name = "your-package";
  src = ./.;
  buildInputs = with pkgs; [
    cmake
    gcc12
    pkg-config
  ];
};
shellHook ​

Runs the shell code prior to initializing the environment. For example, the following hook prints the version of NodeJS for the current environment.

nix
shellHook = ''
   echo "node ${pkgs.nodejs}/bin/node --version"
''
shellHook = ''
   echo "node ${pkgs.nodejs}/bin/node --version"
''
buildInputs ​

Adds build-related dependencies and inputs to your derivation

For example, the mkShell derivation below will have docker and docker-compose in its environment.

outputs = { self, nixpkgs, flake-utils }:
  flake-utils.lib.eachDefaultSystem (system: 
    let 
      pkgs = nixpkgs.legacyPackages.${system};
    in
    {
      devShells.default = pkgs.mkShell {
        buildInputs = [
          pkgs.docker
          pkgs.docker-compose
        ];
      };
    }
  );
outputs = { self, nixpkgs, flake-utils }:
  flake-utils.lib.eachDefaultSystem (system: 
    let 
      pkgs = nixpkgs.legacyPackages.${system};
    in
    {
      devShells.default = pkgs.mkShell {
        buildInputs = [
          pkgs.docker
          pkgs.docker-compose
        ];
      };
    }
  );

stdenv.mkDerivation ​

is a key to understanding how to compose derivations in a flake.nix file.

  • Use buildInputs = [ pkgs.foo pkgs.bar ] to specify the dependencies you want in your environment.
  • Use nativeBuildInputs for packages that would otherwise be available on the base system, but aren't required at runtime, e.g., cmake, gcc, clang, pkg-config, etc
  • Use propogatedBuildInputs for dependencies that you need to propogate to anything using the Flake.