chore(nix): Add dev sub-flake

.envrc

@@ -0,0 +1,2 @@
+watch_file dev/flake.nix
+use flake ./dev

.gitignore

@@ -1,5 +1,7 @@
+/.direnv
+
 /example/data.sqlite*
 /example/result
 
 /test/data.sqlite
-/test/result.txt
+/test/result.txt

dev/flake.nix

@@ -0,0 +1,28 @@
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    treefmt-nix.url = "github:numtide/treefmt-nix";
+    process-compose-flake.url = "github:Platonic-Systems/process-compose-flake";
+  };
+  outputs = inputs@{ self, nixpkgs, flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = nixpkgs.lib.systems.flakeExposed;
+      imports = [
+        inputs.treefmt-nix.flakeModule
+      ];
+      perSystem = { pkgs, lib, config, ... }: {
+        treefmt = {
+          projectRoot = inputs.process-compose-flake;
+          programs = {
+            nixpkgs-fmt.enable = true;
+          };
+        };
+        devShells.default = pkgs.mkShell {
+          inputsFrom = [
+            config.treefmt.build.devShell
+          ];
+        };
+      };
+    };
+}

flake.nix

@@ -15,6 +15,10 @@
         inherit overrideInputs;
         dir = "example";
       };
+      dev = {
+        inherit overrideInputs;
+        dir = "dev";
+      };
     };
   };
 }