From 382289027f92ff3973f14d983a55b183c9b1c0bd Mon Sep 17 00:00:00 2001
From: Silvan Mosberger <contact@infinisil.com>
Date: Mon, 2 Aug 2021 21:18:40 +0200
Subject: [PATCH 1/2] lib/types: Fix emptyValue of listOf and nonEmptyListOf

An empty list is [], not {}!

Also, non-empty lists shouldn't have a default of an empty list!
---
 lib/types.nix | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/types.nix b/lib/types.nix
index f2f9b2bca985..3fa9d881a650 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -390,7 +390,7 @@ rec {
             ).optionalValue
           ) def.value
         ) defs)));
-      emptyValue = { value = {}; };
+      emptyValue = { value = []; };
       getSubOptions = prefix: elemType.getSubOptions (prefix ++ ["*"]);
       getSubModules = elemType.getSubModules;
       substSubModules = m: listOf (elemType.substSubModules m);
@@ -402,7 +402,7 @@ rec {
       let list = addCheck (types.listOf elemType) (l: l != []);
       in list // {
         description = "non-empty " + list.description;
-        # Note: emptyValue is left as is, because another module may define an element.
+        emptyValue = { }; # no .value attr, meaning unset
       };
 
     attrsOf = elemType: mkOptionType rec {

From b333395be54397a62e6befe2bc91664f53306b41 Mon Sep 17 00:00:00 2001
From: Silvan Mosberger <contact@infinisil.com>
Date: Fri, 15 Oct 2021 16:48:38 +0200
Subject: [PATCH 2/2] lib/tests: Add tests for emptyValue

---
 lib/tests/modules.sh              |  9 ++++++++
 lib/tests/modules/emptyValues.nix | 36 +++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)
 create mode 100644 lib/tests/modules/emptyValues.nix

diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index 590937da5b8f..88d152d39352 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -284,6 +284,15 @@ checkConfigOutput '^"a b"$' config.resultFoo ./declare-variants.nix ./define-var
 checkConfigOutput '^"a y z"$' config.resultFooBar ./declare-variants.nix ./define-variant.nix
 checkConfigOutput '^"a b c"$' config.resultFooFoo ./declare-variants.nix ./define-variant.nix
 
+## emptyValue's
+checkConfigOutput "[ ]" config.list.a ./emptyValues.nix
+checkConfigOutput "{ }" config.attrs.a ./emptyValues.nix
+checkConfigOutput "null" config.null.a ./emptyValues.nix
+checkConfigOutput "{ }" config.submodule.a ./emptyValues.nix
+# These types don't have empty values
+checkConfigError 'The option .int.a. is used but not defined' config.int.a ./emptyValues.nix
+checkConfigError 'The option .nonEmptyList.a. is used but not defined' config.nonEmptyList.a ./emptyValues.nix
+
 cat <<EOF
 ====== module tests ======
 $pass Pass
diff --git a/lib/tests/modules/emptyValues.nix b/lib/tests/modules/emptyValues.nix
new file mode 100644
index 000000000000..77825de3281a
--- /dev/null
+++ b/lib/tests/modules/emptyValues.nix
@@ -0,0 +1,36 @@
+{ lib, ... }:
+let
+  inherit (lib) types;
+in {
+
+  options = {
+    int = lib.mkOption {
+      type = types.lazyAttrsOf types.int;
+    };
+    list = lib.mkOption {
+      type = types.lazyAttrsOf (types.listOf types.int);
+    };
+    nonEmptyList = lib.mkOption {
+      type = types.lazyAttrsOf (types.nonEmptyListOf types.int);
+    };
+    attrs = lib.mkOption {
+      type = types.lazyAttrsOf (types.attrsOf types.int);
+    };
+    null = lib.mkOption {
+      type = types.lazyAttrsOf (types.nullOr types.int);
+    };
+    submodule = lib.mkOption {
+      type = types.lazyAttrsOf (types.submodule {});
+    };
+  };
+
+  config = {
+    int.a = lib.mkIf false null;
+    list.a = lib.mkIf false null;
+    nonEmptyList.a = lib.mkIf false null;
+    attrs.a = lib.mkIf false null;
+    null.a = lib.mkIf false null;
+    submodule.a = lib.mkIf false null;
+  };
+
+}