add flake

.envrc

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

flake.nix

@@ -0,0 +1,46 @@
+{
+  inputs = {
+    naersk.url = "github:nix-community/naersk";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    utils.url = "github:numtide/flake-utils";
+    fenix.url = "github:nix-community/fenix";
+    rust-overlay.url = "github:oxalica/rust-overlay";
+  };
+
+  outputs = inputs:
+    with inputs;
+    utils.lib.eachDefaultSystem (system:
+      let
+        overlays = [ (import rust-overlay) ];
+        pkgs = import nixpkgs {
+          inherit system overlays;
+        };
+        naersk-lib = pkgs.callPackage naersk { };
+        nbi = with pkgs; [
+
+          (rust-bin.selectLatestNightlyWith (toolchain: toolchain.default.override {
+            extensions = [ "rust-src" "rust-analyzer" "clippy" ];
+          }))
+          cargo-nextest
+          cargo-criterion
+          pkg-config
+          sccache
+        ];
+
+        bi = with pkgs; [
+          just
+          cargo-watch
+          samply
+        ];
+      in
+      {
+        defaultPackage = naersk-lib.buildPackage ./.;
+        devShell = with pkgs; mkShell {
+          nativeBuildInputs = nbi;
+          buildInputs = bi;
+
+          RUST_SRC_PATH = rustPlatform.rustLibSrc;
+        };
+      }
+    );
+}