From 5b274d5f017ba4d610e495a6fae8a193966e9d25 Mon Sep 17 00:00:00 2001
From: Guillaume Girol <symphorien+git@xlumurb.eu>
Date: Mon, 1 Jan 2024 12:00:00 +0000
Subject: [PATCH] nixos/nix: add workaround for
 https://github.com/NixOS/nix/issues/9487

Nix has a suprising behavior where if the option `extra-foo` is set before `foo`, then setting `foo` overwrites the setting for `extra-foo`. This is reported as https://github.com/NixOS/nix/issues/9487, and will likely not be fixed any time soon.

This works around this issue by always putting `extra-*` settings after non-extra ones in the nixos-generated `/etc/nix.conf`.
---
 nixos/modules/config/nix.nix |  9 ++++++++-
 nixos/tests/all-tests.nix    |  1 +
 nixos/tests/nix-config.nix   | 18 ++++++++++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 nixos/tests/nix-config.nix

diff --git a/nixos/modules/config/nix.nix b/nixos/modules/config/nix.nix
index 2769d8b25ef6..dc39b06013d8 100644
--- a/nixos/modules/config/nix.nix
+++ b/nixos/modules/config/nix.nix
@@ -14,8 +14,10 @@ let
     concatStringsSep
     boolToString
     escape
+    filterAttrs
     floatToString
     getVersion
+    hasPrefix
     isBool
     isDerivation
     isFloat
@@ -95,14 +97,19 @@ let
 
       mkKeyValuePairs = attrs: concatStringsSep "\n" (mapAttrsToList mkKeyValue attrs);
 
+      isExtra = key: hasPrefix "extra-" key;
+
     in
     pkgs.writeTextFile {
       name = "nix.conf";
+      # workaround for https://github.com/NixOS/nix/issues/9487
+      # extra-* settings must come after their non-extra counterpart
       text = ''
         # WARNING: this file is generated from the nix.* options in
         # your NixOS configuration, typically
         # /etc/nixos/configuration.nix.  Do not edit it!
-        ${mkKeyValuePairs cfg.settings}
+        ${mkKeyValuePairs (filterAttrs (key: value: !(isExtra key)) cfg.settings)}
+        ${mkKeyValuePairs (filterAttrs (key: value: isExtra key) cfg.settings)}
         ${cfg.extraOptions}
       '';
       checkPhase = lib.optionalString cfg.checkConfig (
diff --git a/nixos/tests/all-tests.nix b/nixos/tests/all-tests.nix
index 6c0655288c87..10d1986988e6 100644
--- a/nixos/tests/all-tests.nix
+++ b/nixos/tests/all-tests.nix
@@ -596,6 +596,7 @@ in {
   nginx-variants = handleTest ./nginx-variants.nix {};
   nifi = handleTestOn ["x86_64-linux"] ./web-apps/nifi.nix {};
   nitter = handleTest ./nitter.nix {};
+  nix-config = handleTest ./nix-config.nix {};
   nix-ld = handleTest ./nix-ld.nix {};
   nix-serve = handleTest ./nix-serve.nix {};
   nix-serve-ssh = handleTest ./nix-serve-ssh.nix {};
diff --git a/nixos/tests/nix-config.nix b/nixos/tests/nix-config.nix
new file mode 100644
index 000000000000..907e886def35
--- /dev/null
+++ b/nixos/tests/nix-config.nix
@@ -0,0 +1,18 @@
+import ./make-test-python.nix ({ pkgs, ... }:
+{
+  name = "nix-config";
+  nodes.machine = { pkgs, ... }: {
+    nix.settings = {
+      nix-path = [ "nonextra=/etc/value.nix" ];
+      extra-nix-path = [ "extra=/etc/value.nix" ];
+    };
+    environment.etc."value.nix".text = "42";
+  };
+  testScript = ''
+    start_all()
+    machine.wait_for_unit("nix-daemon.socket")
+    # regression test for the workaround for https://github.com/NixOS/nix/issues/9487
+    print(machine.succeed("nix-instantiate --find-file extra"))
+    print(machine.succeed("nix-instantiate --find-file nonextra"))
+  '';
+})