rofi: allow extending themes (#2571)

Move @import and @theme directives to the top of custom theme
definitions so as to allow extending other themes.

modules/programs/rofi.nix

@@ -40,7 +40,12 @@ let
         end = "";
       } name value) + "\n";
 
-  toRasi = attrs: concatStringsSep "\n" (mapAttrsToList mkRasiSection attrs);
+  toRasi = attrs:
+    concatStringsSep "\n" (concatMap (mapAttrsToList mkRasiSection) [
+      (filterAttrs (n: _: n == "@theme") attrs)
+      (filterAttrs (n: _: n == "@import") attrs)
+      (removeAttrs attrs [ "@theme" "@import" ])
+    ]);
 
   locationsMap = {
     center = 0;

tests/modules/programs/rofi/custom-theme.rasi

@@ -1,3 +1,5 @@
+@import "~/.cache/wal/colors-rofi-dark"
+
 #inputbar {
 children: [ prompt,entry ];
 }
@@ -15,5 +17,3 @@ border-color: #FFFFFF;
 foreground-color: rgba ( 250, 251, 252, 100 % );
 width: 512;
 }
-
-@import "~/.cache/wal/colors-rofi-dark"