Merge pull request #357 from NixOS/add-flake-formatter

Add a flake formatter (so `nix fmt` works)

Author: jfly

default.nix

@@ -140,4 +140,6 @@ build
   inherit checks;
 
   ci = pkgs.linkFarm "ci" checks;
+
+  treefmt = treefmtEval.config.build.wrapper;
 }

flake.nix

@@ -22,6 +22,8 @@
         checks = result.checks;
 
         devShells.default = result.shell;
+
+        formatter = result.treefmt;
       }
     );
 }