lib: implement setPrio

For when `hiPrio` and `lowPrio` are not enough.

lib/default.nix

@@ -94,7 +94,7 @@ let
       callPackageWith callPackagesWith extendDerivation hydraJob
       makeScope;
     inherit (meta) addMetaAttrs dontDistribute setName updateName
-      appendToName mapDerivationAttrset lowPrio lowPrioSet hiPrio
+      appendToName mapDerivationAttrset setPrio lowPrio lowPrioSet hiPrio
       hiPrioSet;
     inherit (sources) pathType pathIsDirectory cleanSourceFilter
       cleanSource sourceByRegex sourceFilesBySuffices

lib/meta.nix

@@ -41,16 +41,18 @@ rec {
     let x = builtins.parseDrvName name; in "${x.name}-${suffix}-${x.version}");
 
 
-  /* Apply a function to each derivation and only to derivations in an attrset
+  /* Apply a function to each derivation and only to derivations in an attrset.
   */
   mapDerivationAttrset = f: set: lib.mapAttrs (name: pkg: if lib.isDerivation pkg then (f pkg) else pkg) set;
 
+  /* Set the nix-env priority of the package.
+  */
+  setPrio = priority: addMetaAttrs { inherit priority; };
 
   /* Decrease the nix-env priority of the package, i.e., other
      versions/variants of the package will be preferred.
   */
-  lowPrio = drv: addMetaAttrs { priority = 10; } drv;
-
+  lowPrio = setPrio 10;
 
   /* Apply lowPrio to an attrset with derivations
   */
@@ -60,8 +62,7 @@ rec {
   /* Increase the nix-env priority of the package, i.e., this
      version/variant of the package will be preferred.
   */
-  hiPrio = drv: addMetaAttrs { priority = -10; } drv;
-
+  hiPrio = setPrio (-10);
 
   /* Apply hiPrio to an attrset with derivations
   */