lib/tests: Add submodule file propagation test

lib/tests/modules.sh

@@ -194,6 +194,10 @@ checkConfigOutput '^"submodule"$' options.submodule.type.description ./declare-s
 ## Paths should be allowed as values and work as expected
 checkConfigOutput '^true$' config.submodule.enable ./declare-submoduleWith-path.nix
 
+# Check the file location information is propagated into submodules
+checkConfigOutput the-file.nix config.submodule.internalFiles.0 ./submoduleFiles.nix
+
+
 # Check that disabledModules works recursively and correctly
 checkConfigOutput '^true$' config.enable ./disable-recursive/main.nix
 checkConfigOutput '^true$' config.enable ./disable-recursive/{main.nix,disable-foo.nix}

lib/tests/modules/submoduleFiles.nix

@@ -0,0 +1,21 @@
+{ lib, ... }: {
+  options.submodule = lib.mkOption {
+    default = {};
+    type = lib.types.submoduleWith {
+      modules = [ ({ options, ... }: {
+        options.value = lib.mkOption {};
+
+        options.internalFiles = lib.mkOption {
+          default = options.value.files;
+        };
+      })];
+    };
+  };
+
+  imports = [
+    {
+      _file = "the-file.nix";
+      submodule.value = 10;
+    }
+  ];
+}