lib.modules: add mkDerivedConfig

mkDerivedConfig : Option a -> (a -> Definition b) -> Definition b

Create config definitions with the same priority as the definition of another option.
This should be used for option definitions where one option sets the value of another as a convenience.
For instance a config file could be set with a `text` or `source` option, where text translates to a `source`
value using `mkDerivedConfig options.text (pkgs.writeText "filename.conf")`.

It takes care of setting the right priority using `mkOverride`.

1 files changed, 2 insertions, 3 deletions

diff --git a/nixos/modules/system/etc/etc.nix b/nixos/modules/system/etc/etc.nix
index 225a5683e79e5..6cc8c341e6dfa 100644
--- a/nixos/modules/system/etc/etc.nix
+++ b/nixos/modules/system/etc/etc.nix
@@ -172,9 +172,8 @@ in
             target = mkDefault name;
             source = mkIf (config.text != null) (
               let name' = "etc-" + baseNameOf name;
-              in mkOverride
-                (options.text.highestPrio or lib.modules.defaultPriority)
-                (pkgs.writeText name' config.text));
+              in mkDerivedConfig options.text (pkgs.writeText name')
+            );
           };
 
         }));