Merge pull request #14 from hercules-ci/polyfill-functionTo

Polyfill functionTo where it is pressing

lib.nix

@@ -3,9 +3,29 @@ let
   inherit (lib)
     mkOption
     types
-    functionTo
     ;
 
+  # Polyfill functionTo to make sure it has type merging.
+  # Remove 2022-12
+  functionTo =
+    let sample = types.functionTo lib.types.str;
+    in
+    if sample.functor.wrapped._type or null == "option-type"
+    then types.functionTo
+    else
+      elemType: lib.mkOptionType {
+        name = "functionTo";
+        description = "function that evaluates to a(n) ${elemType.description}";
+        check = lib.isFunction;
+        merge = loc: defs:
+          fnArgs: (lib.mergeDefinitions (loc ++ [ "[function body]" ]) elemType (map (fn: { inherit (fn) file; value = fn.value fnArgs; }) defs)).mergedValue;
+        getSubOptions = prefix: elemType.getSubOptions (prefix ++ [ "[function body]" ]);
+        getSubModules = elemType.getSubModules;
+        substSubModules = m: functionTo (elemType.substSubModules m);
+        functor = (lib.defaultFunctor "functionTo") // { type = functionTo; wrapped = elemType; };
+        nestedTypes.elemType = elemType;
+      };
+
   flake-modules-core-lib = {
     evalFlakeModule =
       { self
@@ -30,7 +50,7 @@ let
 
     mkPerSystemType =
       module:
-      types.functionTo (types.submoduleWith {
+      functionTo (types.submoduleWith {
         modules = [ module ];
         shorthandOnlyDefinesConfig = false;
       });