feat: add a Nix flake

.gitignore

@@ -1,4 +1,5 @@
 /target
+/result
 
 # Nix / devenv
 /.devenv/

README.org

@@ -8,6 +8,36 @@ This is a small tool that helps to list the files you have changed (added/modifi
 This can be useful when working with large repositories, as you can run tools on a specific subset of files instead of the entire repository.
 It can be easily integrated into your workflow to streamline your development process.
 
+** Install with Nix
+
+This project is a Nix flake. It gives you the ~git-changed~ package, an overlay and an app.
+
+Run the tool without an installation:
+
+#+begin_src bash
+$ nix run github:function-artisans/git-changed
+#+end_src
+
+Add the flake to your own configuration:
+
+#+begin_src nix
+{
+  inputs.git-changed.url = "github:function-artisans/git-changed";
+}
+#+end_src
+
+Then take the package for your system:
+
+#+begin_src nix
+inputs.git-changed.packages.${system}.default
+#+end_src
+
+Or add the overlay and take ~pkgs.git-changed~:
+
+#+begin_src nix
+nixpkgs.overlays = [ inputs.git-changed.overlays.default ];
+#+end_src
+
 ** Usage
 
 To get the recent changes comparing to the default branch you can type:

flake.nix

@@ -0,0 +1,41 @@
+{
+  description = "Lists files modified since branching off";
+
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs =
+    { self, nixpkgs }:
+    let
+      systems = [
+        "aarch64-darwin"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "x86_64-linux"
+      ];
+
+      forEachSystem = nixpkgs.lib.genAttrs systems;
+    in
+    {
+      overlays.default = final: _prev: {
+        git-changed = final.callPackage ./package.nix { };
+      };
+
+      packages = forEachSystem (system: {
+        git-changed = nixpkgs.legacyPackages.${system}.callPackage ./package.nix { };
+        default = self.packages.${system}.git-changed;
+      });
+
+      apps = forEachSystem (system: rec {
+        git-changed = {
+          type = "app";
+          program = nixpkgs.lib.getExe self.packages.${system}.git-changed;
+          meta.description = "List the files that changed since the branch point";
+        };
+        default = git-changed;
+      });
+
+      checks = forEachSystem (system: {
+        inherit (self.packages.${system}) git-changed;
+      });
+    };
+}

package.nix

@@ -0,0 +1,38 @@
+{
+  lib,
+  rustPlatform,
+  pkg-config,
+  libgit2,
+  git,
+}:
+
+rustPlatform.buildRustPackage {
+  pname = "git-changed";
+  version = "0.0.1";
+
+  src = lib.fileset.toSource {
+    root = ./.;
+    fileset = lib.fileset.unions [
+      ./Cargo.lock
+      ./Cargo.toml
+      ./src
+      ./tests
+    ];
+  };
+
+  cargoLock.lockFile = ./Cargo.lock;
+
+  # Link the libgit2 of nixpkgs. The git2 crate then builds no copy of its own.
+  nativeBuildInputs = [ pkg-config ];
+  buildInputs = [ libgit2 ];
+  env.LIBGIT2_NO_VENDOR = 1;
+
+  # The test scenarios create their repositories with the git command.
+  nativeCheckInputs = [ git ];
+
+  meta = {
+    description = "Lists files modified since branching off";
+    homepage = "https://github.com/function-artisans/git-changed";
+    mainProgram = "git-changed";
+  };
+}