From 244057cf9fe516aad51a689de8519daedf49dc97 Mon Sep 17 00:00:00 2001
From: Winter <winter@winter.cafe>
Date: Mon, 20 Jul 2026 20:23:26 -0400
Subject: [PATCH 1/2] nixos/lib/testing: `builtins.length (lib.attrNames ...) >
 0 -> != to the empty set

---
 nixos/lib/testing/run.nix | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/nixos/lib/testing/run.nix b/nixos/lib/testing/run.nix
index 0b35007f0c0b..b8a850489ffe 100644
--- a/nixos/lib/testing/run.nix
+++ b/nixos/lib/testing/run.nix
@@ -35,8 +35,7 @@ let
     options = {
       devnet = mkOption {
         type = types.bool;
-        default =
-          builtins.length (lib.attrNames containers) > 0 && builtins.length (lib.attrNames nodes) > 0;
+        default = containers != { } && nodes != { };
         defaultText = lib.literalMD "`true` if both VMs and containers are present.";
         description = ''
           This heuristic setting that assumes that the majority of tests requires VMs and containers
@@ -52,7 +51,7 @@ let
       };
       uid-range = mkOption {
         type = types.bool;
-        default = builtins.length (lib.attrNames containers) > 0;
+        default = containers != { };
         defaultText = lib.literalMD "`true` if containers are present.";
         description = "Containers use systemd-nspawn, which requires pid 0 inside of the sandbox. `uid-range` enables that.";
       };

From bb3215658765d60e8086585dfbcd10038599bfdb Mon Sep 17 00:00:00 2001
From: Winter <winter@winter.cafe>
Date: Fri, 3 Jul 2026 19:15:22 -0400
Subject: [PATCH 2/2] nixos/lib/testing: don't require kvm if only containers
 are specified

Allows containers to be run on systems that don't have the `kvm` feature enabled,
like VMs that don't support nested virt.
---
 nixos/lib/testing/run.nix | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/nixos/lib/testing/run.nix b/nixos/lib/testing/run.nix
index b8a850489ffe..f97489f67be5 100644
--- a/nixos/lib/testing/run.nix
+++ b/nixos/lib/testing/run.nix
@@ -57,8 +57,8 @@ let
       };
       kvm = mkOption {
         type = types.bool;
-        default = isLinux;
-        defaultText = lib.literalMD "`true` if built to run on Linux.";
+        default = isLinux && nodes != { };
+        defaultText = lib.literalMD "`true` if built to run on Linux and any virtual machines are specified.";
         description = "Whether Linux KVM virtualization is required when running this test. Can be disabled to allow emulated execution.";
       };
       apple-virt = mkOption {