From 27b26d8dcca11af05a7eddf001602569c0472735 Mon Sep 17 00:00:00 2001
From: Daniel Langbein <daniel@systemli.org>
Date: Fri, 3 Jan 2025 15:43:55 +0100
Subject: [PATCH] feat: test config in a vm

---
 README.md        | 15 +++++++++++++++
 modules/base.nix | 11 +++++++++++
 2 files changed, 26 insertions(+)

diff --git a/README.md b/README.md
index ab0b82f..c1102a0 100644
--- a/README.md
+++ b/README.md
@@ -19,6 +19,7 @@ See also:
       * [Default configuration](#default-configuration)
       * [Apply modified configuration](#apply-modified-configuration)
     * [ARM: Vanilla UEFI bootloader for the Raspberry Pi 3B+](#arm-vanilla-uefi-bootloader-for-the-raspberry-pi-3b)
+  * [Test config changes in a VM](#test-config-changes-in-a-vm)
   * [Update, build and switch](#update-build-and-switch)
     * [tldr](#tldr)
     * [Update](#update)
@@ -158,6 +159,20 @@ Then install NixOS the way you prefer, but don't touch/modify the partition tabl
 
 See https://nixos.wiki/wiki/NixOS_on_ARM/UEFI#Installing
 
+## Test config changes in a VM
+
+https://nix.dev/tutorials/nixos/nixos-configuration-on-vm.html
+
+- See `base.nix` -> `virtualisation.vmVariant` for build-vm specific options
+- Import of `./hardware-configuration.nix`
+  - As build-vm uses `mkVMOverride` we can just leave the import
+  - If in doubt, remove/uncomment it
+
+```shell
+nix-build '<nixpkgs/nixos>' -A vm -I nixos-config=./hosts/yodaTux/configuration.nix
+./result/bin/run-yodaTux-vm && rm yodaTux.qcow2
+```
+
 ## Update, build and switch
 
 ### tldr
diff --git a/modules/base.nix b/modules/base.nix
index f3d856f..e57cf62 100644
--- a/modules/base.nix
+++ b/modules/base.nix
@@ -88,4 +88,15 @@
   # https://nixos.wiki/wiki/Firewall
   # Note: Firewall rules may be bypassed/overwritten by Docker, as per https://github.com/NixOS/nixpkgs/issues/111852
   networking.firewall.enable = true;
+
+  # Options only for build.system.vm - they won’t get applied when building build.system.toplevel aka the normal system config.
+  # https://discourse.nixos.org/t/wayland-compositors-an-build-vm-not-working/46486/2
+  virtualisation.vmVariant = {
+    users.users.yoda.initialPassword = "asdf";
+    virtualisation.qemu.options = [
+      "-device virtio-vga-gl"
+      "-display sdl,gl=on,show-cursor=off"
+      "-m 8G"
+    ];
+  };
 }