lib.evalModules: Add extendModules and type to result

Allows the simultaneous construction of top-level invocations and
submodule types.

This helps structure configuration systems integration code.

lib/modules.nix

@@ -60,7 +60,8 @@ rec {
      it is to transparently move a set of modules to be a submodule of another
      config (as the proper arguments need to be replicated at each call to
      evalModules) and the less declarative the module set is. */
-  evalModules = { modules
+  evalModules = evalModulesArgs@
+                { modules
                 , prefix ? []
                 , # This should only be used for special arguments that need to be evaluated
                   # when resolving module structure (like in imports). For everything else,
@@ -183,10 +184,26 @@ rec {
             else throw baseMsg
         else null;
 
-      result = builtins.seq checkUnmatched {
-        inherit options;
-        config = removeAttrs config [ "_module" ];
-        inherit (config) _module;
+      checked = builtins.seq checkUnmatched;
+
+      result = {
+        options = checked options;
+        config = checked (removeAttrs config [ "_module" ]);
+        _module = checked (config._module);
+
+        extendModules = extendArgs@{
+          modules ? [],
+          specialArgs ? {},
+          prefix ? [],
+          }:
+            evalModules (evalModulesArgs // {
+              modules = evalModulesArgs.modules ++ modules;
+              specialArgs = evalModulesArgs.specialArgs or {} // specialArgs;
+              prefix = extendArgs.prefix or evalModulesArgs.prefix;
+            });
+        type = lib.types.submoduleWith {
+          inherit modules specialArgs;
+        };
       };
     in result;
 

lib/tests/modules.sh

@@ -179,6 +179,13 @@ checkConfigOutput "true" config.submodule.outer ./declare-submoduleWith-modules.
 # which evaluates all the modules defined by the type)
 checkConfigOutput "submodule" options.submodule.type.description ./declare-submoduleWith-modules.nix
 
+## submodules can be declared using (evalModules {...}).type
+checkConfigOutput "true" config.submodule.inner ./declare-submodule-via-evalModules.nix
+checkConfigOutput "true" config.submodule.outer ./declare-submodule-via-evalModules.nix
+# Should also be able to evaluate the type name (which evaluates freeformType,
+# which evaluates all the modules defined by the type)
+checkConfigOutput "submodule" options.submodule.type.description ./declare-submodule-via-evalModules.nix
+
 ## Paths should be allowed as values and work as expected
 checkConfigOutput "true" config.submodule.enable ./declare-submoduleWith-path.nix
 

lib/tests/modules/declare-submodule-via-evalModules.nix

@@ -0,0 +1,28 @@
+{ lib, ... }: {
+  options.submodule = lib.mkOption {
+    inherit (lib.evalModules {
+      modules = [
+        {
+          options.inner = lib.mkOption {
+            type = lib.types.bool;
+            default = false;
+          };
+        }
+      ];
+    }) type;
+    default = {};
+  };
+
+  config.submodule = lib.mkMerge [
+    ({ lib, ... }: {
+      options.outer = lib.mkOption {
+        type = lib.types.bool;
+        default = false;
+      };
+    })
+    {
+      inner = true;
+      outer = true;
+    }
+  ];
+}

lib/types.nix

@@ -505,17 +505,36 @@ rec {
           then setFunctionArgs (args: unify (value args)) (functionArgs value)
           else unify (if shorthandOnlyDefinesConfig then { config = value; } else value);
 
-        allModules = defs: modules ++ imap1 (n: { value, file }:
+        allModules = defs: imap1 (n: { value, file }:
           if isAttrs value || isFunction value then
             # Annotate the value with the location of its definition for better error messages
             coerce (lib.modules.unifyModuleSyntax file "${toString file}-${toString n}") value
           else value
         ) defs;
 
-        freeformType = (evalModules {
-          inherit modules specialArgs;
-          args.name = "‹name›";
-        })._module.freeformType;
+        base = evalModules {
+          inherit specialArgs;
+          modules = [{
+            # This is a work-around for the fact that some sub-modules,
+            # such as the one included in an attribute set, expects an "args"
+            # attribute to be given to the sub-module. As the option
+            # evaluation does not have any specific attribute name yet, we
+            # provide a default for the documentation and the freeform type.
+            #
+            # This is necessary as some option declaration might use the
+            # "name" attribute given as argument of the submodule and use it
+            # as the default of option declarations.
+            #
+            # We use lookalike unicode single angle quotation marks because
+            # of the docbook transformation the options receive. In all uses
+            # > and < wouldn't be encoded correctly so the encoded values
+            # would be used, and use of `<` and `>` would break the XML document.
+            # It shouldn't cause an issue since this is cosmetic for the manual.
+            _module.args.name = lib.mkOptionDefault "‹name›";
+          }] ++ modules;
+        };
+
+        freeformType = base._module.freeformType;
 
       in
       mkOptionType rec {
@@ -523,32 +542,13 @@ rec {
         description = freeformType.description or name;
         check = x: isAttrs x || isFunction x || path.check x;
         merge = loc: defs:
-          (evalModules {
-            modules = allModules defs;
-            inherit specialArgs;
-            args.name = last loc;
+          (base.extendModules {
+            modules = [ { _module.args.name = last loc; } ] ++ allModules defs;
             prefix = loc;
           }).config;
         emptyValue = { value = {}; };
-        getSubOptions = prefix: (evalModules
-          { 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
-            # evaluation does not have any specific attribute name, we
-            # provide a default one for the documentation.
-            #
-            # This is mandatory as some option declaration might use the
-            # "name" attribute given as argument of the submodule and use it
-            # as the default of option declarations.
-            #
-            # Using lookalike unicode single angle quotation marks because
-            # of the docbook transformation the options receive. In all uses
-            # &gt; and &lt; wouldn't be encoded correctly so the encoded values
-            # would be used, and use of `<` and `>` would break the XML document.
-            # It shouldn't cause an issue since this is cosmetic for the manual.
-            args.name = "‹name›";
-          }).options // optionalAttrs (freeformType != null) {
+        getSubOptions = prefix: (base.extendModules
+          { inherit prefix; }).options // optionalAttrs (freeformType != null) {
             # Expose the sub options of the freeform type. Note that the option
             # discovery doesn't care about the attribute name used here, so this
             # is just to avoid conflicts with potential options from the submodule