refactor(dotfiles): share Nix file discovery

src/dotfiles/default.nix

@@ -17,7 +17,7 @@ let
   util = import ./util.nix { inherit lib; };
 
   registry = import ./registry.nix {
-    inherit lib;
+    inherit lib util;
     hosts = self.nixosConfigurations;
     root = root + "/registry";
   };

src/dotfiles/guests.nix

@@ -8,6 +8,7 @@
   util,
 }:
 let
+  files = util.collectNixFiles root;
   mkGuest =
     name:
     { config, lib, ... }:
@@ -167,22 +168,22 @@ let
       config = lib.mkIf cfg.enable {
         assertions =
           let
-            hasDirectorySettings = mount: mount.owner != null || mount.group != null || mount.mode != null;
-            hasCompleteDirectorySettings =
-              mount: mount.owner != null && mount.group != null && mount.mode != null;
-            hasOneSource = mount: (mount.directory != null) != (mount.file != null);
             mountsWithInvalidSource = lib.attrNames (
               lib.filterAttrs (_: mount: !hasOneSource mount) cfg.mounts
             );
+            hasOneSource = mount: (mount.directory != null) != (mount.file != null);
             fileMountsWithHostSettings = lib.attrNames (
               lib.filterAttrs (_: mount: mount.file != null && hasDirectorySettings mount) cfg.mounts
             );
+            hasDirectorySettings = mount: mount.owner != null || mount.group != null || mount.mode != null;
             directoryMountsWithPartialHostSettings = lib.attrNames (
               lib.filterAttrs (
                 _: mount:
                 mount.directory != null && hasDirectorySettings mount && !hasCompleteDirectorySettings mount
               ) cfg.mounts
             );
+            hasCompleteDirectorySettings =
+              mount: mount.owner != null && mount.group != null && mount.mode != null;
           in
           [
             {
@@ -275,11 +276,7 @@ let
       };
     };
 
-  files = util.collectNixFiles root;
-  guestFiles = lib.filterAttrs (file: type: type == "regular" && lib.hasSuffix ".nix" file) (
-    builtins.readDir root
-  );
-  names = map (file: lib.removeSuffix ".nix" file) (lib.attrNames guestFiles);
+  names = map (path: lib.removeSuffix ".nix" (builtins.baseNameOf path)) files;
 in
 {
   imports = files ++ map mkGuest names;

src/dotfiles/registry.nix

@@ -2,20 +2,14 @@
   hosts,
   lib,
   root,
+  util,
 }:
 let
-  definitions =
-    lib.mapAttrs'
-      (
-        name: _type:
-        let
-          path = root + "/${name}";
-        in
-        lib.nameValuePair (registryName name) (mkRegistry path)
-      )
-      (
-        lib.filterAttrs (name: type: type == "regular" && lib.hasSuffix ".nix" name) (builtins.readDir root)
-      );
+  definitions = lib.listToAttrs (
+    map (path: lib.nameValuePair (registryName (builtins.baseNameOf path)) (mkRegistry path)) (
+      util.collectNixFiles root
+    )
+  );
 
   registryName = fileName: lib.removeSuffix ".nix" fileName;
 

src/skills/style/nix/rules/general.md

@@ -0,0 +1,12 @@
+## Discover Nix files
+
+### Rule
+
+Use `util.collectNixFiles` to discover Nix files.
+Do not use `builtins.readDir` with a `.nix` suffix filter for this purpose.
+Pass `util` to Nix functions that need the helper.
+
+### Rationale
+
+`util.collectNixFiles` centralizes recursive discovery of Nix files.
+Repository Nix code uses one implementation.