modules/overlays: Make overlay .nix files be plain overlay functions

Also restructure modules/overlays/default.nix to account for this; move all
overlay options into default.nix and load the overlay functions conditionally
from there.

1 files changed, 14 insertions, 5 deletions

diff --git a/modules/overlays/default.nix b/modules/overlays/default.nix
index 60253ca..745673a 100644
--- a/modules/overlays/default.nix
+++ b/modules/overlays/default.nix
@@ -1,8 +1,17 @@
-{ ... }:
+{ lib, config, ... }:
 
+let cfg = config.this.overlays;
+    overlay = ov:
+      lib.optional cfg."${ov}".enable
+        (import ./${ov}.nix);
+in
 {
-  imports = [
-    ./emacs.nix
-    ./g45_h264.nix
-  ];
+  options = {
+    this.overlays.emacs.enable = lib.mkEnableOption "custom-built Emacs overlay";
+    this.overlays.g45_h264.enable = lib.mkEnableOption "intel-vaapi-driver with h264 support on gm45";
+  };
+
+  config.nixpkgs.overlays =
+    (overlay "emacs") ++
+    (overlay "g45_h264");
 }