refactor: modularize checks into separate Nix files

- Extracted checks (clippy, doc, fmt, and toml-fmt) into modularized Nix files under `nix/checks`.
- Updated `flake.nix` to import checks from the new modularized structure.
- Improved clarity and maintainability by separating concerns for each check.

flake.nix

@@ -6,12 +6,12 @@
     crane.url = "github:ipetkov/crane";
   };
   outputs =
-    { self
-    , nixpkgs
-    , flake-utils
-    , rust-overlay
-    , crane
-    ,
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+      rust-overlay,
+      crane,
     }:
     flake-utils.lib.eachDefaultSystem (
       system:
@@ -25,6 +25,11 @@
             allowUnfree = true;
           };
         };
+
+        # Import rust setup
+        rustSetup = import ./nix/rust-setup.nix { inherit pkgs crane; };
+        inherit (rustSetup) rustVersion rustPlatform craneLib;
+
         src = craneLib.cleanCargoSource ./.;
 
         commonArgs = {
@@ -57,10 +62,6 @@
           doCheck = false;
         };
 
-        # Import rust setup
-        rustSetup = import ./nix/rust-setup.nix { inherit pkgs crane; };
-        inherit (rustSetup) rustVersion rustPlatform craneLib;
-
         # Import vault-hier package
         vault-hier = import ./nix/packages/vault-hier.nix {
           inherit
@@ -76,29 +77,16 @@
         };
       in
       {
-        checks = {
-          inherit vault-hier;
-
-          my-workspace-clippy = craneLib.cargoClippy (commonArgs // {
-            inherit cargoArtifacts;
-            cargoClippyExtraArgs = "--all-targets -- --deny warnings";
-          });
-
-          my-workspace-doc = craneLib.cargoDoc (commonArgs // {
-            inherit cargoArtifacts;
-          });
-
-          # Check formatting
-          my-workspace-fmt = craneLib.cargoFmt {
-            inherit src;
-          };
-
-          my-workspace-toml-fmt = craneLib.taploFmt {
-            src = pkgs.lib.sources.sourceFilesBySuffices src [ ".toml" ];
-            # taplo arguments can be further customized below as needed
-            # taploExtraArgs = "--config ./taplo.toml";
-          };
-
+        # Import checks
+        checks = import ./nix/checks {
+          inherit
+            craneLib
+            src
+            commonArgs
+            cargoArtifacts
+            vault-hier
+            pkgs
+            ;
         };
 
         # Add packages output

nix/checks/clippy.nix

@@ -0,0 +1,13 @@
+{
+  craneLib,
+  commonArgs,
+  cargoArtifacts,
+}:
+
+craneLib.cargoClippy (
+  commonArgs
+  // {
+    inherit cargoArtifacts;
+    cargoClippyExtraArgs = "--all-targets -- --deny warnings";
+  }
+)

nix/checks/default.nix

@@ -0,0 +1,30 @@
+{
+  craneLib,
+  src,
+  commonArgs,
+  cargoArtifacts,
+  vault-hier,
+  pkgs,
+}:
+
+{
+  inherit vault-hier;
+
+  my-workspace-clippy = import ./clippy.nix {
+    inherit craneLib commonArgs cargoArtifacts;
+  };
+
+  my-workspace-doc = import ./doc.nix {
+    inherit craneLib commonArgs cargoArtifacts;
+  };
+
+  # Check formatting
+  my-workspace-fmt = import ./fmt.nix {
+    inherit craneLib src;
+  };
+
+  my-workspace-toml-fmt = import ./toml-fmt.nix {
+    inherit craneLib src;
+    lib = pkgs.lib;
+  };
+}

nix/checks/doc.nix

@@ -0,0 +1,12 @@
+{
+  craneLib,
+  commonArgs,
+  cargoArtifacts,
+}:
+
+craneLib.cargoDoc (
+  commonArgs
+  // {
+    inherit cargoArtifacts;
+  }
+)

nix/checks/fmt.nix

@@ -0,0 +1,5 @@
+{ craneLib, src }:
+
+craneLib.cargoFmt {
+  inherit src;
+}

nix/checks/toml-fmt.nix

@@ -0,0 +1,11 @@
+{
+  craneLib,
+  src,
+  lib,
+}:
+
+craneLib.taploFmt {
+  src = lib.sources.sourceFilesBySuffices src [ ".toml" ];
+  # taplo arguments can be further customized below as needed
+  # taploExtraArgs = "--config ./taplo.toml";
+}