build(nix): add minimal flake.nix

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -1,2 +1,9 @@
+# Nix
+result
+result-*
+
+# direnv
+.direnv/
+
 # macOS
 .DS_Store

flake.nix

@@ -0,0 +1,36 @@
+{
+  description = "Dev environment for Rust based on Nix flakes";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+    fenix = {
+      url = "github:nix-community/fenix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs = { self, nixpkgs, flake-utils, fenix }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+        rustToolchain = fenix.packages.${system}.minimal.toolchain;
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          buildInputs = [
+            rustToolchain
+          ];
+        };
+
+        checks.default = pkgs.runCommand "check-rust-env" {
+          buildInputs = [ rustToolchain ];
+        } ''
+          if ! command -v rustc > /dev/null || ! command -v cargo > /dev/null; then
+            exit 1
+          fi
+          touch $out
+        '';
+      }
+    );
+}