Replace hlint shell job with check derivation.

.github/workflows/formatting.yaml

@@ -30,4 +30,4 @@ jobs:
 
     - name: 📐 Check hlint
       run: |
-        nix develop .#fmt --command hlint .
+        nix build .#checks.x86_64-linux.hlint

flake.nix

@@ -4,6 +4,10 @@
     haskellNix.url = "github:input-output-hk/haskell.nix";
     iohk-nix.url = "github:input-output-hk/iohk-nix";
     flake-utils.url = "github:numtide/flake-utils";
+    lint-utils = {
+      url = "github:homotopic/lint-utils";
+      inputs.nixpkgs.follows = "haskellNix/nixpkgs";
+    };
     CHaP = {
       url = "github:input-output-hk/cardano-haskell-packages?ref=repo";
       flake = false;
@@ -33,6 +37,9 @@
       (system:
       let
         pkgs = import inputs.nixpkgs { inherit system; };
+        tools = {
+          hlint = hydraProject.pkgs.haskell-nix.tool hydraProject.compiler "hlint" "3.8";
+        };
         hydraProject = import ./nix/hydra/project.nix {
           inherit (inputs) haskellNix iohk-nix CHaP;
           inherit system nixpkgs;
@@ -58,8 +65,12 @@
             spec = import ./spec { inherit pkgs; };
           };
 
+        checks = let lu = inputs.lint-utils.linters.${system}; in {
+          hlint = lu.hlint { src = self; hlint = tools.hlint; };
+        };
+
         devShells = (import ./nix/hydra/shell.nix {
-          inherit inputs hydraProject system;
+          inherit inputs hydraProject tools system;
         }) // {
           ci = (import ./nix/hydra/shell.nix {
             inherit inputs hydraProject system;

nix/hydra/shell.nix

@@ -7,6 +7,7 @@
   withoutDevTools ? false
 , hydraProject
 , inputs
+, tools
 , system ? builtins.currentSystem
 }:
 let
@@ -16,7 +17,6 @@ let
 
   fourmolu = pkgs.haskell-nix.tool compiler "fourmolu" "0.14.0.0";
   cabal-fmt = pkgs.haskell-nix.tool compiler "cabal-fmt" "0.1.9";
-  hlint = pkgs.haskell-nix.tool compiler "hlint" "3.8";
   apply-refact = pkgs.haskell-nix.tool compiler "apply-refact" "0.14.0.0";
 
   # Build HLS form our fork (see flake.nix)
@@ -47,7 +47,7 @@ let
     fourmolu
     cabal-fmt
     pkgs.nixpkgs-fmt
-    hlint
+    tools.hlint
     apply-refact
     # For validating JSON instances against a pre-defined schema
     pkgs.check-jsonschema
@@ -159,7 +159,7 @@ let
       fourmolu
       cabal-fmt
       pkgs.nixpkgs-fmt
-      hlint
+      tools.hlint
       apply-refact
     ];
   };