Revamp treefmt use via flake-parts module (#75)

Get rid of `treefmt.toml` as that is nixified.

README.md

@@ -21,7 +21,7 @@ For details, see: https://srid.ca/haskell-template/start
 
 - Run `nix flake update` to update all flake inputs.
 - Run `nix --option sandbox false build .#check -L` to run the flake checks.
-- Run `, fmt` in nix shell to autoformat the project. This uses [treefmt](https://github.com/numtide/treefmt), which uses `./treefmt.toml` (where fourmolu and nixpkgs-fmt are specified).
+- Run `, fmt` in nix shell to autoformat the project. This uses [treefmt](https://github.com/numtide/treefmt).
 - Run `, docs` to start Hoogle with packages in your cabal file.
 - Run the application without installing: `nix run github:srid/haskell-template` (or `nix run .` from checkout)
 - Common workflows

flake.lock

@@ -123,21 +123,22 @@
         "haskell-flake": "haskell-flake",
         "mission-control": "mission-control",
         "nixpkgs": "nixpkgs_2",
-        "treefmt-flake": "treefmt-flake"
+        "treefmt-nix": "treefmt-nix"
       }
     },
-    "treefmt-flake": {
+    "treefmt-nix": {
       "locked": {
-        "lastModified": 1669929251,
-        "narHash": "sha256-+qgCD89JyZhBNF4m/HuuVrpoRoXMTl5F60mJzr3QPNM=",
-        "owner": "srid",
-        "repo": "treefmt-flake",
-        "rev": "86341cd4a0ce21556a348fd27a4797997d27be00",
+        "lastModified": 1671645275,
+        "narHash": "sha256-aHpd0f/WBO4a3kK7wy8tsp4iGTOGEAY3sL/ujOLkqw0=",
+        "owner": "Platonic-Systems",
+        "repo": "treefmt-nix",
+        "rev": "8280dec5403061434de195b81854d65e6613b5ca",
         "type": "github"
       },
       "original": {
-        "owner": "srid",
-        "repo": "treefmt-flake",
+        "owner": "Platonic-Systems",
+        "ref": "flake-module",
+        "repo": "treefmt-nix",
         "type": "github"
       }
     }

flake.nix

@@ -4,7 +4,7 @@
     nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
     flake-parts.url = "github:hercules-ci/flake-parts";
     haskell-flake.url = "github:srid/haskell-flake";
-    treefmt-flake.url = "github:srid/treefmt-flake";
+    treefmt-nix.url = "github:Platonic-Systems/treefmt-nix/flake-module"; # https://github.com/numtide/treefmt-nix/pull/14
     flake-root.url = "github:srid/flake-root";
     mission-control.url = "github:Platonic-Systems/mission-control";
   };
@@ -14,7 +14,7 @@
       systems = nixpkgs.lib.systems.flakeExposed;
       imports = [
         inputs.haskell-flake.flakeModule
-        inputs.treefmt-flake.flakeModule
+        inputs.treefmt-nix.flakeModule
         inputs.flake-root.flakeModule
         inputs.mission-control.flakeModule
       ];
@@ -25,7 +25,9 @@
           packages = {
             haskell-template.root = ./.;
           };
-          buildTools = hp: { } // config.treefmt.formatters;
+          buildTools = hp: {
+            treefmt = config.treefmt.wrapper;
+          } // config.treefmt.programs;
           # overrides = self: super: {}
           hlsCheck.enable = true;
           hlintCheck.enable = true;
@@ -33,12 +35,22 @@
 
         # Auto formatters. This also adds a flake check to ensure that the
         # source tree was auto formatted.
-        treefmt.formatters = {
-          inherit (pkgs)
-            nixpkgs-fmt;
-          inherit (pkgs.haskellPackages)
-            cabal-fmt
-            fourmolu;
+        treefmt.config = {
+          package = pkgs.treefmt;
+          projectRootFile = "flake.nix";
+
+          programs.ormolu.enable = true;
+          programs.ormolu.package = pkgs.haskellPackages.fourmolu;
+          settings.formatter.ormolu = {
+            options = [
+              "--ghc-opt"
+              "-XImportQualifiedPost"
+            ];
+          };
+
+          programs.nixpkgs-fmt.enable = true;
+
+          programs.cabal-fmt.enable = true;
         };
 
         # Dev shell scripts.
@@ -60,7 +72,7 @@
           };
           fmt = {
             description = "Format the source tree";
-            exec = "${lib.getExe pkgs.treefmt}";
+            exec = "${lib.getExe config.treefmt.wrapper}";
             category = "Dev Tools ";
           };
           run = {

treefmt.toml

@@ -1,21 +0,0 @@
-[formatter.haskell]
-command = "fourmolu"
-options = [
-    "--ghc-opt",
-    "-XImportQualifiedPost",
-    "--ghc-opt",
-    "-XTypeApplications",
-    "--mode",
-    "inplace",
-    "--check-idempotence",
-]
-includes = ["*.hs"]
-
-[formatter.nix]
-command = "nixpkgs-fmt"
-includes = ["*.nix"]
-
-[formatter.cabal]
-command = "cabal-fmt"
-options = ["--inplace"]
-includes = ["*.cabal"]