From eec83d41e3e7d9ad5bc1086198d972d55bab1203 Mon Sep 17 00:00:00 2001
From: Silvan Mosberger <contact@infinisil.com>
Date: Tue, 31 Dec 2019 04:25:35 +0100
Subject: [PATCH] lib/types: Allow paths as submodule values

---
 lib/types.nix                                 | 8 +++++---
 nixos/doc/manual/development/option-types.xml | 6 +++---
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/lib/types.nix b/lib/types.nix
index de3c4f0d603032..847a4e902cab60 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -376,14 +376,16 @@ rec {
           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
+          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;
 
       in
       mkOptionType rec {
         name = "submodule";
-        check = x: isAttrs x || isFunction x;
+        check = x: isAttrs x || isFunction x || path.check x;
         merge = loc: defs:
           (evalModules {
             modules = allModules defs;
diff --git a/nixos/doc/manual/development/option-types.xml b/nixos/doc/manual/development/option-types.xml
index 1ec7e3efad714b..173fdfcbbc8334 100644
--- a/nixos/doc/manual/development/option-types.xml
+++ b/nixos/doc/manual/development/option-types.xml
@@ -257,9 +257,9 @@
     <listitem>
      <para>
       A set of sub options <replaceable>o</replaceable>.
-      <replaceable>o</replaceable> can be an attribute set or a function
-      returning an attribute set. Submodules are used in composed types to
-      create modular options. This is equivalent to
+      <replaceable>o</replaceable> can be an attribute set, a function
+      returning an attribute set, or a path to a file containing such a value. Submodules are used in
+      composed types to create modular options. This is equivalent to
       <literal>types.submoduleWith { modules = toList o; shorthandOnlyDefinesConfig = true; }</literal>.
       Submodules are detailed in
       <xref