Add Nix flake

README.md

@@ -86,6 +86,22 @@ WebAssembly backend.
 
 [wasm-pack]: https://rustwasm.github.io/wasm-pack/
 
+### Nix flake
+
+There is a Nix flake available in the `contrib` directory. With it, you can get
+a reproducible build of Jotdown by cloning the repo and running
+
+```
+$ nix build ./contrib
+```
+
+If you want to the run Jotdown CLI on any system that has Nix installed, you can
+do it like this:
+
+```
+$ nix run github:hellux/jotdown?dir=contrib -- <arguments..>
+```
+
 ## Status
 
 ### Correctness

contrib/flake.nix

@@ -0,0 +1,50 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+
+    crane = {
+      url = "github:ipetkov/crane";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
+    flake-utils.url = "github:numtide/flake-utils";
+
+    fenix = {
+      url = "github:nix-community/fenix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs = {
+    nixpkgs,
+    crane,
+    flake-utils,
+    fenix,
+    ...
+  }:
+    flake-utils.lib.eachDefaultSystem (system: let
+      pkgs = import nixpkgs {
+        inherit system;
+      };
+
+      toolchain = with fenix.packages.${system};
+        combine [
+          default.rustc
+          default.cargo
+          default.clippy
+          default.rustfmt
+        ];
+
+      craneLib = (crane.mkLib pkgs).overrideToolchain toolchain;
+      buildInputs = with pkgs; [];
+    in rec {
+      packages.default = craneLib.buildPackage {
+        inherit buildInputs;
+        src = pkgs.lib.cleanSourceWith {src = craneLib.path ../.;};
+      };
+
+      apps.default = flake-utils.lib.mkApp {
+        drv = packages.default;
+      };
+    });
+}