From da7cb17f9eec592d2c958f96e27e5b0d017e6897 Mon Sep 17 00:00:00 2001
From: Peder Bergebakken Sundt <pbsds@hotmail.com>
Date: Sat, 31 May 2025 19:13:33 +0200
Subject: [PATCH] base: stabilize system.build.toplevel.outPath for vmVariant

This is done by not depending on the flake itself, allowing the bits of a dirty tree to not affect the hash.
This enables equivalence testing with `just eval-vm bob` and checking if the system closure hash changes or not.
---
 base/nix.nix                   | 17 +++++++++++------
 base/services/auto-upgrade.nix | 20 +++++++++++---------
 2 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/base/nix.nix b/base/nix.nix
index a485cdb..5e21fc6 100644
--- a/base/nix.nix
+++ b/base/nix.nix
@@ -1,4 +1,4 @@
-{ inputs, ... }:
+{ lib, config, inputs, ... }:
 {
   nix = {
     gc = {
@@ -21,11 +21,16 @@
     ** use the same channel the system
     ** was built with
     */
-    registry = {
-      "nixpkgs".flake = inputs.nixpkgs;
-      "nixpkgs-unstable".flake = inputs.nixpkgs-unstable;
-      "pvv-nix".flake = inputs.self;
-    };
+    registry = lib.mkMerge [
+      {
+        "nixpkgs".flake = inputs.nixpkgs;
+        "nixpkgs-unstable".flake = inputs.nixpkgs-unstable;
+      }
+      # We avoid the reference to self in vmVariant to get a stable system .outPath for equivalence testing
+      (lib.mkIf (!config.virtualisation.isVmVariant) {
+        "pvv-nix".flake = inputs.self;
+      })
+    ];
     nixPath = [
       "nixpkgs=${inputs.nixpkgs}"
       "unstable=${inputs.nixpkgs-unstable}"
diff --git a/base/services/auto-upgrade.nix b/base/services/auto-upgrade.nix
index 098d744..8d90b66 100644
--- a/base/services/auto-upgrade.nix
+++ b/base/services/auto-upgrade.nix
@@ -1,4 +1,4 @@
-{ inputs, pkgs, lib, ... }:
+{ config, inputs, pkgs, lib, ... }:
 
 let
   inputUrls = lib.mapAttrs (input: value: value.url) (import "${inputs.self}/flake.nix").inputs;
@@ -26,12 +26,14 @@ in
 
   # workaround for https://github.com/NixOS/nix/issues/6895
   # via https://git.lix.systems/lix-project/lix/issues/400
-  environment.etc."current-system-flake-inputs.json".source
-    = pkgs.writers.writeJSON "flake-inputs.json" (
-      lib.flip lib.mapAttrs inputs (name: input:
-        # inputs.*.sourceInfo sans outPath, since writeJSON will otherwise serialize sourceInfo like a derivation
-        lib.removeAttrs (input.sourceInfo or {}) [ "outPath" ]
-          // { store-path = input.outPath; } # comment this line if you don't want to retain a store reference to the flake inputs
-      )
-    );
+  environment.etc = lib.mkIf (!config.virtualisation.isVmVariant) {
+    "current-system-flake-inputs.json".source
+      = pkgs.writers.writeJSON "flake-inputs.json" (
+        lib.flip lib.mapAttrs inputs (name: input:
+          # inputs.*.sourceInfo sans outPath, since writeJSON will otherwise serialize sourceInfo like a derivation
+          lib.removeAttrs (input.sourceInfo or {}) [ "outPath" ]
+            // { store-path = input.outPath; } # comment this line if you don't want to retain a store reference to the flake inputs
+        )
+      );
+  };
 }