Add treefmt check (#36)

Also add garnix checks.

flake.lock

@@ -55,7 +55,23 @@
       "inputs": {
         "flake-parts": "flake-parts",
         "haskell-flake": "haskell-flake",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "treefmt-flake": "treefmt-flake"
+      }
+    },
+    "treefmt-flake": {
+      "locked": {
+        "lastModified": 1660759207,
+        "narHash": "sha256-qr2OrIS6jDpUkc91rmaMoZ+m4RWSDQ/odve9/DLtSsY=",
+        "owner": "srid",
+        "repo": "treefmt-flake",
+        "rev": "7b2e2975513a5a4a87f9b87926de3f00722ec67c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "srid",
+        "repo": "treefmt-flake",
+        "type": "github"
       }
     }
   },

flake.nix

@@ -5,25 +5,30 @@
     flake-parts.url = "github:hercules-ci/flake-parts";
     flake-parts.inputs.nixpkgs.follows = "nixpkgs";
     haskell-flake.url = "github:srid/haskell-flake";
+    treefmt-flake.url = "github:srid/treefmt-flake";
   };
 
-  outputs = { self, nixpkgs, flake-parts, haskell-flake, ... }:
+  outputs = { self, nixpkgs, flake-parts, haskell-flake, treefmt-flake, ... }:
     flake-parts.lib.mkFlake { inherit self; } {
       systems = nixpkgs.lib.systems.flakeExposed;
       imports = [
         haskell-flake.flakeModule
+        treefmt-flake.flakeModule
       ];
-      perSystem = { self', pkgs, ... }: {
+      perSystem = { self', config, pkgs, ... }: {
         haskellProjects.default = {
           root = ./.;
           buildTools = hp: {
             inherit (pkgs)
-              treefmt
-              nixpkgs-fmt;
-            inherit (hp)
-              cabal-fmt
-              fourmolu;
-          };
+              treefmt;
+          } // config.treefmt.formatters;
+        };
+        treefmt.formatters = {
+          inherit (pkgs)
+            nixpkgs-fmt;
+          inherit (pkgs.haskellPackages)
+            cabal-fmt
+            fourmolu;
         };
       };
     };

garnix.yaml

@@ -2,6 +2,8 @@ builds:
   include:
     - "packages.x86_64-linux.*"
     - "packages.aarch64-darwin.*"
+    - "checks.x86_64-linux.*"
+    - "checks.aarch64-darwin.*"
     - "devShells.x86_64-linux.default"
     - "devShells.aarch64-darwin.default"
   exclude: []