flake: fix and refactor the homeManagerModules alias (#1287)

Fixes: 0e5b1613bd ("stylix: rename homeManagerModules to homeModules (#1267)")
Link: https://github.com/danth/stylix/pull/1287

Reviewed-by: NAHO <90870942+trueNAHO@users.noreply.github.com>

flake/default.nix

@@ -1,5 +1,6 @@
 {
   imports = [
+    ./deprecated.nix
     ./dev-shell.nix
     ./modules.nix
     ./packages.nix

flake/deprecated.nix

@@ -0,0 +1,19 @@
+{
+  lib,
+  self,
+  ...
+}:
+{
+  # NOTE: the `flake` submodule has a `lazyAttrsOf` freeform type.
+  #
+  # This means a `mkIf false` definition will not omit the attr, because
+  # `lazyAttrsOf` adds an "empty value" stub throwing "used but not defined".
+  #
+  # Therefore, instead of doing `flake.foo = mkIf` you should do `flake = mkIf (…) { foo = …; }`.
+  # If you need multiple definitions with different conditions, use `flake = mkMerge [ … ]`.
+
+  # Drop this alias after 26.05
+  flake = lib.mkIf (!lib.oldestSupportedReleaseIsAtLeast 2605) {
+    homeManagerModules = builtins.warn "stylix: flake output `homeManagerModules` has been renamed to `homeModules`" self.homeModules;
+  };
+}

flake/modules.nix

@@ -23,11 +23,6 @@
         ];
       };
 
-    # Drop this alias after 26.05
-    homeManagerModules = lib.mkIf (lib.oldestSupportedReleaseIsAtLeast 2511) (
-      builtins.warn "stylix: flake output `homeManagerModules` has been renamed to `homeModules`" self.homeModules
-    );
-
     homeModules.stylix =
       { pkgs, ... }@args:
       {