From 426ab31fdeb828886c22ec0e561eca2b90b84b94 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Mon, 22 Nov 2021 14:39:44 +0100
Subject: [PATCH 1/2] modules: Document that extendModules is also a module
 argument

---
 lib/modules.nix | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lib/modules.nix b/lib/modules.nix
index 92ddc8c5bc70..b381487f68e3 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -74,6 +74,8 @@ rec {
             override existing configuration fundamentally requires a new
             fixpoint to be constructed.
 
+            This is also available as a module argument.
+
       ‘_module’: A portion of the configuration tree which is elided from
             ‘config’. It contains some values that are mostly internal to the
             module system implementation.

From d464ccfdd9e101d4f5a112ab58d91ccbb912524a Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Mon, 22 Nov 2021 14:39:10 +0100
Subject: [PATCH 2/2] modules: Add moduleType to module arguments

---
 lib/modules.nix                        |  3 +++
 lib/tests/modules.sh                   |  5 +++++
 lib/tests/modules/declare-variants.nix |  9 +++++++++
 lib/tests/modules/define-variant.nix   | 22 ++++++++++++++++++++++
 4 files changed, 39 insertions(+)
 create mode 100644 lib/tests/modules/declare-variants.nix
 create mode 100644 lib/tests/modules/define-variant.nix

diff --git a/lib/modules.nix b/lib/modules.nix
index b381487f68e3..2468b6fbdd22 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -62,6 +62,8 @@ rec {
       ‘type’: A module system type representing the module set as a submodule,
             to be extended by configuration from the containing module set.
 
+            This is also available as the module argument ‘moduleType’.
+
       ‘extendModules’: A function similar to ‘evalModules’ but building on top
             of the module set. Its arguments, ‘modules’ and ‘specialArgs’ are
             added to the existing values.
@@ -148,6 +150,7 @@ rec {
         config = {
           _module.args = {
             inherit extendModules;
+            moduleType = type;
           } // args;
         };
       };
diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index aba3f08122f5..2f36d6107ca4 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -281,6 +281,11 @@ checkConfigError 'A definition for option .fun.\[function body\]. is not of type
 checkConfigOutput "b a" config.result ./functionTo/list-order.nix
 checkConfigOutput "a c" config.result ./functionTo/merging-attrs.nix
 
+# moduleType
+checkConfigOutput "a b" config.resultFoo ./declare-variants.nix ./define-variant.nix
+checkConfigOutput "a y z" config.resultFooBar ./declare-variants.nix ./define-variant.nix
+checkConfigOutput "a b c" config.resultFooFoo ./declare-variants.nix ./define-variant.nix
+
 cat <<EOF
 ====== module tests ======
 $pass Pass
diff --git a/lib/tests/modules/declare-variants.nix b/lib/tests/modules/declare-variants.nix
new file mode 100644
index 000000000000..3ed6fa689e21
--- /dev/null
+++ b/lib/tests/modules/declare-variants.nix
@@ -0,0 +1,9 @@
+{ lib, moduleType, ... }:
+let inherit (lib) mkOption types;
+in
+{
+  options.variants = mkOption {
+    type = types.lazyAttrsOf moduleType;
+    default = {};
+  };
+}
diff --git a/lib/tests/modules/define-variant.nix b/lib/tests/modules/define-variant.nix
new file mode 100644
index 000000000000..423cb0e37cb5
--- /dev/null
+++ b/lib/tests/modules/define-variant.nix
@@ -0,0 +1,22 @@
+{ config, lib, ... }:
+let inherit (lib) types mkOption attrNames;
+in
+{
+  options = {
+    attrs = mkOption { type = types.attrsOf lib.types.int; };
+    result = mkOption { };
+    resultFoo = mkOption { };
+    resultFooBar = mkOption { };
+    resultFooFoo = mkOption { };
+  };
+  config = {
+    attrs.a = 1;
+    variants.foo.attrs.b = 1;
+    variants.bar.attrs.y = 1;
+    variants.foo.variants.bar.attrs.z = 1;
+    variants.foo.variants.foo.attrs.c = 3;
+    resultFoo = lib.concatMapStringsSep " " toString (attrNames config.variants.foo.attrs);
+    resultFooBar = lib.concatMapStringsSep " " toString (attrNames config.variants.foo.variants.bar.attrs);
+    resultFooFoo = lib.concatMapStringsSep " " toString (attrNames config.variants.foo.variants.foo.attrs);
+  };
+}