lib/types: Add types.submoduleWith for more flexibility than types.submodule

lib/types.nix

@@ -358,25 +358,41 @@ rec {
     };
 
     # A submodule (like typed attribute set). See NixOS manual.
-    submodule = opts:
+    submodule = modules: submoduleWith {
+      shorthandOnlyDefinesConfig = true;
+      modules = toList modules;
+    };
+
+    submoduleWith =
+      { modules
+      , specialArgs ? {}
+      , shorthandOnlyDefinesConfig ? false
+      }@attrs:
       let
-        opts' = toList opts;
         inherit (lib.modules) evalModules;
+
+        coerce = unify: value: if isFunction value
+          then setFunctionArgs (args: unify (value args)) (functionArgs value)
+          else unify (if shorthandOnlyDefinesConfig then { config = value; } else value);
+
+        allModules = defs: modules ++ imap1 (n: { value, file }:
+          # Annotate the value with the location of its definition for better error messages
+          coerce (lib.modules.unifyModuleSyntax file "${toString file}-${toString n}") value
+        ) defs;
+
       in
       mkOptionType rec {
         name = "submodule";
         check = x: isAttrs x || isFunction x;
         merge = loc: defs:
-          let
+          (evalModules {
-            coerce = def: if isFunction def then def else { config = def; };
+            modules = allModules defs;
-            modules = opts' ++ map (def: { _file = def.file; imports = [(coerce def.value)]; }) defs;
+            inherit specialArgs;
-          in (evalModules {
-            inherit modules;
             args.name = last loc;
             prefix = loc;
           }).config;
         getSubOptions = prefix: (evalModules
-          { modules = opts'; inherit prefix;
+          { inherit modules prefix specialArgs;
             # This is a work-around due to the fact that some sub-modules,
             # such as the one included in an attribute set, expects a "args"
             # attribute to be given to the sub-module. As the option
@@ -394,13 +410,29 @@ rec {
             # It shouldn't cause an issue since this is cosmetic for the manual.
             args.name = "‹name›";
           }).options;
-        getSubModules = opts';
+        getSubModules = modules;
-        substSubModules = m: submodule m;
+        substSubModules = m: submoduleWith (attrs // {
-        functor = (defaultFunctor name) // {
+          modules = m;
-          # Merging of submodules is done as part of mergeOptionDecls, as we have to annotate
+        });
-          # each submodule with its location.
+        functor = defaultFunctor name // {
-          payload = [];
+          type = types.submoduleWith;
-          binOp = lhs: rhs: [];
+          payload = {
+            modules = modules;
+            specialArgs = specialArgs;
+            shorthandOnlyDefinesConfig = shorthandOnlyDefinesConfig;
+          };
+          binOp = lhs: rhs: {
+            modules = lhs.modules ++ rhs.modules;
+            specialArgs =
+              let intersecting = builtins.intersectAttrs lhs.specialArgs rhs.specialArgs;
+              in if intersecting == {}
+              then lhs.specialArgs // rhs.specialArgs
+              else throw "A submoduleWith option is declared multiple times with the same specialArgs \"${toString (attrNames intersecting)}\"";
+            shorthandOnlyDefinesConfig =
+              if lhs.shorthandOnlyDefinesConfig == rhs.shorthandOnlyDefinesConfig
+              then lhs.shorthandOnlyDefinesConfig
+              else throw "A submoduleWith option is declared multiple times with conflicting shorthandOnlyDefinesConfig values";
+          };
         };
       };