feat: add flag to choose between backends

.envrc

@@ -0,0 +1,11 @@
+if ! has nix_direnv_version || ! nix_direnv_version 2.2.1; then
+  source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/2.2.1/direnvrc" "sha256-zelF0vLbEl5uaqrfIzbgNzJWGmLzCmYAkInj/LNxvKs="
+fi
+
+nix_direnv_watch_file devenv.nix
+nix_direnv_watch_file devenv.lock
+nix_direnv_watch_file devenv.yaml
+if ! use flake . --impure
+then
+  echo "devenv could not be built. The devenv environment was not loaded. Make the necessary changes to devenv.nix and hit enter to try again." >&2
+fi

.gitignore

@@ -16,3 +16,5 @@ test_book/book/
 # Ignore Vim temporary and swap files.
 *.sw?
 *~
+.devenv
+.direnv

flake.nix

@@ -0,0 +1,43 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.05";
+    systems.url = "github:nix-systems/default";
+    devenv.url = "github:cachix/devenv";
+    fenix.url = "github:nix-community/fenix";
+    fenix.inputs.nixpkgs.follows = "nixpkgs";
+  };
+
+  nixConfig = {
+    extra-trusted-public-keys = "devenv.cachix.org-1:w1cLUi8dv3hnoSPGAuibQv+f9TZLr6cv/Hm9XgU50cw=";
+    extra-substituters = "https://devenv.cachix.org";
+  };
+
+  outputs = { self, nixpkgs, devenv, systems, ... } @ inputs:
+    let
+      forEachSystem = nixpkgs.lib.genAttrs (import systems);
+    in
+    {
+      packages = forEachSystem (system: {
+        devenv-up = self.devShells.${system}.default.config.procfileScript;
+      });
+
+      devShells = forEachSystem
+        (system:
+          let
+            pkgs = nixpkgs.legacyPackages.${system};
+          in
+          {
+            default = devenv.lib.mkShell {
+              inherit inputs pkgs;
+              modules = [
+                {
+                  # https://devenv.sh/reference/options/
+                  packages = [];
+                  languages.rust.enable = true;
+                  languages.rust.channel = "stable";
+                }
+              ];
+            };
+          });
+    };
+}