lib/modules: Improve error when a configuration is imported

This is appears to be a fairly common mistake for beginners who want
to build larger things from the system configurations, such as NixOps
networks, etc. Further explanation seems appropriate.

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/tests/modules/import-configuration.nix b/lib/tests/modules/import-configuration.nix
new file mode 100644
index 00000000000..a2a32bbee4c
--- /dev/null
+++ b/lib/tests/modules/import-configuration.nix
@@ -0,0 +1,12 @@
+{ lib, ... }:
+let
+  myconf = lib.evalModules { modules = [ { } ]; };
+in
+{
+  imports = [
+    # We can't do this. A configuration is not equal to its set of a modules.
+    # Equating those would lead to a mess, as specialArgs, anonymous modules
+    # that can't be deduplicated, and possibly more come into play.
+    myconf
+  ];
+}