Add nix build for reference

.github/workflows/nix.yml

@@ -0,0 +1,24 @@
+name: NixOS/nix
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+  schedule:
+    - cron: '0 9 * * 1'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: cachix/install-nix-action@v20
+      with:
+        nix_path: nixpkgs=channel:nixos-unstable
+    - uses: DeterminateSystems/magic-nix-cache-action@v2
+    - run: nix build .
+    - run: ls -lah result/bin/
+    - run: sha256sum result/bin/repro-env
+    - run: result/bin/repro-env --help
+    - run: ldd result/bin/repro-env

flake.nix

@@ -0,0 +1,37 @@
+{
+  inputs = {
+    fenix.url = "github:nix-community/fenix";
+    flake-utils.url = "github:numtide/flake-utils";
+    naersk.url = "github:nix-community/naersk";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  };
+
+  outputs = { self, fenix, flake-utils, naersk, nixpkgs }:
+    flake-utils.lib.eachDefaultSystem (
+      system: let
+        pkgs = (import nixpkgs) {
+          inherit system;
+        };
+
+        toolchain = with fenix.packages.${system};
+          combine [
+            stable.rustc
+            stable.cargo
+            targets.x86_64-unknown-linux-musl.stable.rust-std
+          ];
+
+        naersk' = naersk.lib.${system}.override {
+          cargo = toolchain;
+          rustc = toolchain;
+        };
+
+      in rec {
+        defaultPackage = naersk'.buildPackage {
+          src = ./.;
+          nativeBuildInputs = with pkgs; [ pkgsStatic.stdenv.cc ];
+          CARGO_BUILD_TARGET = "x86_64-unknown-linux-musl";
+          CARGO_BUILD_RUSTFLAGS = "-C target-feature=+crt-static";
+        };
+      }
+    );
+}