From 1bd4da1848cb7b68858ebb2ca1f8b0e5fed46c58 Mon Sep 17 00:00:00 2001
From: Matt Sturgeon <matt@sturgeon.me.uk>
Date: Fri, 20 Sep 2024 09:11:32 +0100
Subject: [PATCH 1/2] nixos/nixpkgs: fix `config` assertion text

The assertion message should include the `nixpkgs.config` value, however
it currently includes the entire `nixpkgs.config` _option_.

This means the type, declarations, definitions, etc were all printed.
---
 nixos/modules/misc/nixpkgs.nix      |  2 +-
 nixos/modules/misc/nixpkgs/test.nix | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/misc/nixpkgs.nix b/nixos/modules/misc/nixpkgs.nix
index 44903a15c5ca0..f83ab9e59cf87 100644
--- a/nixos/modules/misc/nixpkgs.nix
+++ b/nixos/modules/misc/nixpkgs.nix
@@ -386,7 +386,7 @@ in
           `nixpkgs.config` options should be passed when creating the instance instead.
 
           Current value:
-          ${lib.generators.toPretty { multiline = true; } opt.config}
+          ${lib.generators.toPretty { multiline = true; } cfg.config}
         '';
       }
     ];
diff --git a/nixos/modules/misc/nixpkgs/test.nix b/nixos/modules/misc/nixpkgs/test.nix
index be9a88a077887..a2cb2f834776c 100644
--- a/nixos/modules/misc/nixpkgs/test.nix
+++ b/nixos/modules/misc/nixpkgs/test.nix
@@ -16,6 +16,10 @@ let
     nixpkgs.hostPlatform = "aarch64-linux";
     nixpkgs.buildPlatform = "aarch64-linux";
   };
+  externalPkgsWithConfig = {
+    nixpkgs.pkgs = pkgs;
+    nixpkgs.config.allowUnfree = true;
+  };
   ambiguous = {
     _file = "ambiguous.nix";
     nixpkgs.hostPlatform = "aarch64-linux";
@@ -108,6 +112,17 @@ lib.recurseIntoAttrs {
           For a future proof system configuration, we recommend to remove
           the legacy definitions.
         ''];
+    assert builtins.trace (lib.head (getErrors externalPkgsWithConfig))
+      getErrors externalPkgsWithConfig ==
+        [''
+          Your system configures nixpkgs with an externally created instance.
+          `nixpkgs.config` options should be passed when creating the instance instead.
+
+          Current value:
+          {
+            allowUnfree = true;
+          }
+        ''];
     assert getErrors {
         nixpkgs.localSystem = pkgs.stdenv.hostPlatform;
         nixpkgs.hostPlatform = pkgs.stdenv.hostPlatform;

From 6d9dfef94ffd59a327573eea7bc709a84c44b3d2 Mon Sep 17 00:00:00 2001
From: Matt Sturgeon <matt@sturgeon.me.uk>
Date: Fri, 20 Sep 2024 09:25:37 +0100
Subject: [PATCH 2/2] nixos/nixpkgs: show definition files in `config`
 assertion

---
 nixos/modules/misc/nixpkgs.nix      | 3 +++
 nixos/modules/misc/nixpkgs/test.nix | 4 ++++
 2 files changed, 7 insertions(+)

diff --git a/nixos/modules/misc/nixpkgs.nix b/nixos/modules/misc/nixpkgs.nix
index f83ab9e59cf87..4048fd6857378 100644
--- a/nixos/modules/misc/nixpkgs.nix
+++ b/nixos/modules/misc/nixpkgs.nix
@@ -387,6 +387,9 @@ in
 
           Current value:
           ${lib.generators.toPretty { multiline = true; } cfg.config}
+
+          Defined in:
+          ${lib.concatMapStringsSep "\n" (file: "  - ${file}") opt.config.files}
         '';
       }
     ];
diff --git a/nixos/modules/misc/nixpkgs/test.nix b/nixos/modules/misc/nixpkgs/test.nix
index a2cb2f834776c..e70b7a12e8dd7 100644
--- a/nixos/modules/misc/nixpkgs/test.nix
+++ b/nixos/modules/misc/nixpkgs/test.nix
@@ -17,6 +17,7 @@ let
     nixpkgs.buildPlatform = "aarch64-linux";
   };
   externalPkgsWithConfig = {
+    _file = "ext-pkgs-config.nix";
     nixpkgs.pkgs = pkgs;
     nixpkgs.config.allowUnfree = true;
   };
@@ -122,6 +123,9 @@ lib.recurseIntoAttrs {
           {
             allowUnfree = true;
           }
+
+          Defined in:
+            - ext-pkgs-config.nix
         ''];
     assert getErrors {
         nixpkgs.localSystem = pkgs.stdenv.hostPlatform;