neovim: better default package definition

home/modules/neovim.nix

@@ -3,7 +3,7 @@
 let
   cfg = config.snowhawk.neovim;
 
-  nightlyPackage = inputs.neovim-overlay.packages.${pkgs.system}.default;
+  nightlyNeovim = inputs.neovim-overlay.packages.${pkgs.system}.default;
 in
 {
   options.snowhawk.neovim = {
@@ -11,8 +11,9 @@ in
 
     nightly = lib.mkEnableOption "nightly build of neovim";
 
-    package = lib.mkPackageOption pkgs "neovim" {
-      default = [ "neovim-unwrapped" ];
+    package = lib.mkOption {
+      type = with lib.types; package;
+      default = if cfg.nightly then nightlyNeovim else pkgs.neovim-unwrapped;
     };
   };
   config =
@@ -26,8 +27,6 @@ in
       };
     in
     lib.mkIf cfg.enable {
-      snowhawk.neovim.package = lib.mkIf cfg.nightly (lib.mkDefault nightlyPackage);
-
       # Set nvim as manpager and default editor
       home.sessionVariables = {
         EDITOR = "nvim";

lib/default.nix

@@ -1,6 +1,6 @@
 final: prev:
 let
-  inherit (prev) isFunction;
+  inherit (prev) isFunction mkMerge mkIf;
 in
 rec {
   # Ternary operator
@@ -15,4 +15,9 @@ rec {
   right = f: g: tern (isFunction g)
     (right (x: f (g (x))))
     (f (g));
+
+  mkIfElse = predicate: yes: no: mkMerge [
+    (mkIf predicate yes)
+    (mkIf (!predicate) no)
+  ];
 }