better flake php

flake.nix

@@ -11,9 +11,24 @@
       formatters = pkgs: {
         "*.php" = pkgs.lib.getExe pkgs.php84.packages.php-cs-fixer;
       };
-      devShell.packages = pkgs: [
-        pkgs.php84.packages.composer
-        pkgs.php84
+      devShell.packages = pkgs: let
+        php_version = "81";
+        php = pkgs.pkgs."php${php_version}".buildEnv {
+          extensions = {
+            enabled,
+            all,
+          }:
+            enabled
+            ++ (with all; [
+              dom
+              simplexml
+              tokenizer
+              filter
+            ]);
+        };
+      in [
+        php.packages.composer
+        php
       ];
     };
 }