lib/modules: Throw earlier when module function does not return attrs

`m` must always be an attrset at this point. It is basically always
evaluated. This will make it throw when any of the attrs is accessed,
rather than just `config`. We assume that this will improve the error
message in more scenarios.

1 files changed, 20 insertions, 0 deletions

diff --git a/lib/tests/modules/deferred-module-error.nix b/lib/tests/modules/deferred-module-error.nix
new file mode 100644
index 000000000000..d48ae092e8fe
--- /dev/null
+++ b/lib/tests/modules/deferred-module-error.nix
@@ -0,0 +1,20 @@
+{ config, lib, ... }:
+let
+  inherit (lib) types mkOption setDefaultModuleLocation evalModules;
+  inherit (types) deferredModule lazyAttrsOf submodule str raw enum;
+in
+{
+  options = {
+    deferred = mkOption {
+      type = deferredModule;
+    };
+    result = mkOption {
+      default = (evalModules { modules = [ config.deferred ]; }).config.result;
+    };
+  };
+  config = {
+    deferred = { ... }:
+      # this should be an attrset, so this fails
+      true;
+  };
+}