From 6ec9d187b71ba19b72717e38bc2c3e56b3872eaa Mon Sep 17 00:00:00 2001
From: maralorn <mail@maralorn.de>
Date: Mon, 6 Mar 2023 23:18:36 +0100
Subject: [PATCH] Improve test-config script

---
 nixos/roles/laminar/test-config.nix | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/nixos/roles/laminar/test-config.nix b/nixos/roles/laminar/test-config.nix
index 3ca7739c..5c31fd32 100644
--- a/nixos/roles/laminar/test-config.nix
+++ b/nixos/roles/laminar/test-config.nix
@@ -64,7 +64,6 @@ in {
   ];
   systemd.services = {
     update-config = {
-      path = [pkgs.git pkgs.nix pkgs.openssh pkgs.nixos-rebuild pkgs.builders-configurator];
       restartIfChanged = false;
       unitConfig.X-StopOnRemoval = false;
       serviceConfig = {
@@ -81,6 +80,7 @@ in {
               "Control.Exception qualified as Exception"
               "Data.ByteString.Char8 qualified as BSC"
             ];
+            bins = [pkgs.nix-diff pkgs.jq];
           } ''
             exitOnError = \msg action -> try action >>= \case
                 Left (_ :: Exception.IOException) -> say msg >> exitSuccess
@@ -90,15 +90,20 @@ in {
 
             main = do
               cd "/etc/nixos"
-              exitOnError "Cannot pull forward git config." do void do git ["pull", "--ff-only"]
-              current_commit <- BSC.strip <$> (exitOnError "Current system is from a dirty commit." do readFileBS "/run/current-system/config-commit")
+              void $ git ["pull", "--ff-only"]
               new_system <- readlink "-f" "/var/cache/gc-links/test-config/nixos-configurations/hera" |> captureTrim
+              old_system <- readlink "-f" "/run/current-system" |> captureTrim
+              when (new_system == old_system) do say "No changes."; exitSuccess
+              let switch = do
+                   nix_env "-p" "/nix/var/nix/profiles/system" "--set" (decodeUtf8 new_system :: String)
+                   exe ([i|#{new_system}/bin/switch-to-configuration|] :: String) "switch"
+                   exitSuccess
+              diff_is_small <- (== "[]") <$> (nix_diff "--json" [new_system, "/run/current-system"] |> jq ".inputsDiff.inputDerivationDiffs" |> captureTrim)
+              when diff_is_small switch
+              current_commit <- BSC.strip <$> (exitOnError "Current system is from a dirty commit." do readFileBS "/run/current-system/config-commit")
               new_commit <- BSC.strip <$> readFileBS [i|#{new_system}/config-commit|]
-              when (current_commit == new_commit) do say "No changes." >> exitSuccess
               is_direct_forward <- ("" ==) <$> (git ["log", "-n1", "--oneline", [i|^#{new_commit}|], decodeUtf8 current_commit])
-              when is_direct_forward do
-                nix_env "-p" "/nix/var/nix/profiles/system" "--set" (decodeUtf8 new_system :: String)
-                exe ([i|#{new_system}/bin/switch-to-configuration|] :: String) "switch"
+              when is_direct_forward switch
           '';
       in
         lib.getExe haskell_script;