From 9a8b7640e010b901fb528cf62cf0bc79e0912ae2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Anselm=20Sch=C3=BCler?= <mail@anselmschueler.com>
Date: Sun, 3 Apr 2022 15:12:18 +0200
Subject: [PATCH 1/2] =?UTF-8?q?nixos/doc/types:=20note=20submodules?=
 =?UTF-8?q?=E2=80=99=20default=E2=80=99s=20behaviour?=
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---
 nixos/doc/manual/development/option-types.section.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/nixos/doc/manual/development/option-types.section.md b/nixos/doc/manual/development/option-types.section.md
index 00f1d85bdb61..d32d4fc50ad7 100644
--- a/nixos/doc/manual/development/option-types.section.md
+++ b/nixos/doc/manual/development/option-types.section.md
@@ -308,6 +308,10 @@ The option set can be defined directly
 ([Example: Directly defined submodule](#ex-submodule-direct)) or as reference
 ([Example: Submodule defined as a reference](#ex-submodule-reference)).
 
+Note that even if your submodule’s options all have a default value,
+you will still need to provide a default value (e.g. an empty attribute set)
+if you want to allow users to leave it undefined.
+
 ::: {#ex-submodule-direct .example}
 ::: {.title}
 **Example: Directly defined submodule**

From 8e68f3fcfc9eb2a00aae46bfb7f6f27a87f920f0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Anselm=20Sch=C3=BCler?= <mail@anselmschueler.com>
Date: Sun, 3 Apr 2022 16:44:09 +0200
Subject: [PATCH 2/2] nixos/doc: build manual

---
 .../doc/manual/from_md/development/option-types.section.xml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/nixos/doc/manual/from_md/development/option-types.section.xml b/nixos/doc/manual/from_md/development/option-types.section.xml
index 444729292702..c67e183581c2 100644
--- a/nixos/doc/manual/from_md/development/option-types.section.xml
+++ b/nixos/doc/manual/from_md/development/option-types.section.xml
@@ -617,6 +617,12 @@
       (<link linkend="ex-submodule-reference">Example: Submodule defined
       as a reference</link>).
     </para>
+    <para>
+      Note that even if your submodule’s options all have a default
+      value, you will still need to provide a default value (e.g. an
+      empty attribute set) if you want to allow users to leave it
+      undefined.
+    </para>
     <anchor xml:id="ex-submodule-direct" />
     <para>
       <emphasis role="strong">Example: Directly defined