refactor: switch from numtide/flake-utils to flake-parts

flake.nix

@@ -9,34 +9,47 @@
     };
 
     nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
-
-    utils.url = "github:numtide/flake-utils";
   };
 
-  outputs = { self, flake-compat, nixpkgs, utils }:
-    # For each supported platform,
-    utils.lib.eachDefaultSystem (system:
-      let
+  outputs = inputs @ {flake-parts, ...}:
+    inputs.flake-parts.lib.mkFlake {inherit inputs;} {
+      flake = {
+        overlays.default = import ./pkgs/phps.nix inputs.nixpkgs;
+      };
+
+      systems = [
+        "x86_64-linux"
+        "x86_64-darwin"
+        "aarch64-linux"
+        "aarch64-darwin"
+      ];
+
+      perSystem = {
+        config,
+        pkgs,
+        system,
+        ...
+      }: let
         # Let’s merge the package set from Nixpkgs with our custom PHP versions.
-        pkgs = import nixpkgs.outPath {
+        pkgs = import inputs.nixpkgs {
           config = {
             allowUnfree = true;
           };
           inherit system;
           overlays = [
-            self.overlays.default
+            inputs.self.overlays.default
           ];
         };
       in rec {
+        formatter = pkgs.alejandra;
+
         packages = {
           inherit (pkgs) php php56 php70 php71 php72 php73 php74 php80 php81 php82;
         };
 
         checks = import ./checks.nix {
           inherit packages pkgs system;
         };
-      }
-    ) // {
-      overlays.default = import ./pkgs/phps.nix nixpkgs.outPath;
+      };
     };
 }