Update nixpkgs, and use treefmt

.github/workflows/ci.yaml

@@ -9,13 +9,17 @@ jobs:
       MAINLINE: refs/heads/master
     steps:
       - uses: actions/checkout@v2
-      - uses: cachix/install-nix-action@v16
+      - uses: cachix/install-nix-action@v17
         with:
-          install_url: https://nixos-nix-install-tests.cachix.org/serve/i6laym9jw3wg9mw6ncyrk6gjx4l34vvx/install
-          install_options: "--tarball-url-prefix https://nixos-nix-install-tests.cachix.org/serve"
           extra_nix_config: |
             experimental-features = nix-command flakes
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+      - name: Cache Nix dependencies
+        run: |
+          nix develop -j 4 -c echo
+      - name: Format check
+        run: |
+          nix develop -j auto -c treefmt --fail-on-change
       - name: Build 🔧
         run: |
           nix build -j4 --no-link

flake.lock

@@ -31,56 +31,19 @@
         "type": "github"
       }
     },
-    "flake-utils_2": {
-      "locked": {
-        "lastModified": 1644229661,
-        "narHash": "sha256-1YdnJAsNy69bpcjuoKdOYQX0YxZBiCYZo4Twxerqv7k=",
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "rev": "3cecb5b042f7f209c56ffd8371b2711a290ec797",
-        "type": "github"
-      },
-      "original": {
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "type": "github"
-      }
-    },
-    "lint-utils": {
-      "inputs": {
-        "flake-utils": "flake-utils_2",
-        "nixpkgs": [
-          "nixpkgs"
-        ]
-      },
-      "locked": {
-        "lastModified": 1650427214,
-        "narHash": "sha256-9m66rRSSM614ocRXNPAArwnrS6zzCQYYhd3nw8g4QUg=",
-        "ref": "overengineered",
-        "rev": "5555def5a25c5437834c06cbe79b3945916ec59f",
-        "revCount": 28,
-        "type": "git",
-        "url": "https://gitlab.homotopic.tech/nix/lint-utils.git"
-      },
-      "original": {
-        "ref": "overengineered",
-        "type": "git",
-        "url": "https://gitlab.homotopic.tech/nix/lint-utils.git"
-      }
-    },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1650882267,
-        "narHash": "sha256-BFKiz8srATQIBuFEN2HgS2EHisK29EjZ/HV34wSr2lU=",
+        "lastModified": 1651634615,
+        "narHash": "sha256-VtvcS61bLh5mIBm9cV3idUHdlfPRFus/NwdJfaj5s8o=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "2ea2f7b6d0cb7ce0712f2aa80303cda08deb0de2",
+        "rev": "abfd31179174133ab8131139d650297bf4da63b7",
         "type": "github"
       },
       "original": {
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "2ea2f7b6d0cb7ce0712f2aa80303cda08deb0de2",
+        "rev": "abfd31179174133ab8131139d650297bf4da63b7",
         "type": "github"
       }
     },
@@ -88,7 +51,6 @@
       "inputs": {
         "flake-compat": "flake-compat",
         "flake-utils": "flake-utils",
-        "lint-utils": "lint-utils",
         "nixpkgs": "nixpkgs"
       }
     }

flake.nix

@@ -1,17 +1,11 @@
 {
   description = "Ema project";
   inputs = {
-    nixpkgs.url = "github:nixos/nixpkgs/2ea2f7b6d0cb7ce0712f2aa80303cda08deb0de2";
+    nixpkgs.url = "github:nixos/nixpkgs/abfd31179174133ab8131139d650297bf4da63b7";
     flake-utils.url = "github:numtide/flake-utils";
     flake-utils.inputs.nixpkgs.follows = "nixpkgs";
     flake-compat.url = "github:edolstra/flake-compat";
     flake-compat.flake = false;
-    lint-utils = {
-      type = "git";
-      url = "https://gitlab.homotopic.tech/nix/lint-utils.git";
-      ref = "overengineered";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
   };
   outputs = inputs@{ self, nixpkgs, flake-utils, ... }:
     flake-utils.lib.eachDefaultSystem
@@ -39,17 +33,9 @@
                     haskell-language-server
                     ormolu
                     pkgs.nixpkgs-fmt
+                    pkgs.treefmt
                   ]);
             };
-
-          lintSpec = {
-            nixpkgs-fmt = { };
-            cabal-fmt = { };
-            fourmolu = {
-              ghcOpts = "-o-XTypeApplications -o-XImportQualifiedPost";
-            };
-          };
-
         in
         rec {
           # Used by `nix build`
@@ -63,29 +49,6 @@
             default = emaProject false;
           };
 
-          # Used by `nix run ...`
-          apps = {
-            format = inputs.lint-utils.mkApp.${system} lintSpec;
-          };
-
-          # Used by `nix flake check` (but see next attribute)
-          checks = {
-            format = inputs.lint-utils.mkChecks.${system} lintSpec;
-          };
-
-          # We need this hack because `nix flake check` won't work for Haskell
-          # projects: https://nixos.wiki/wiki/Import_From_Derivation#IFD_and_Haskell
-          #
-          # Instead, run: `nix build .#check.x86_64-linux` (replace with your system)
-          check =
-            pkgs.runCommand "combined-checks"
-              {
-                checksss = builtins.attrValues self.checks.${system};
-              } ''
-              echo $checksss
-              touch $out
-            '';
-
         }) // {
       herculesCI.ciSystems = [ "x86_64-linux" ];
     };

treefmt.toml

@@ -0,0 +1,16 @@
+[formatter.haskell]
+command = "fourmolu"
+options = [
+    "--ghc-opt",
+    "-XImportQualifiedPost",
+    "--ghc-opt",
+    "-XTypeApplications",
+    "--mode",
+    "inplace",
+    "--check-idempotence",
+]
+includes = ["*.hs"]
+
+[formatter.nix]
+command = "nixpkgs-fmt"
+includes = ["*.nix"]