Fix bug that led to no derived functions for function arguments and a…

…dd test.

src/_gettsim/policy_environment_postprocessor.py

@@ -75,7 +75,6 @@ def add_derived_functions_to_functions_tree(
 
     """
     names_of_columns_in_data = tree_flatten_with_qualified_name(data)[0]
-
     # Create derived functions
     (
         time_conversion_functions,

src/_gettsim/shared.py

@@ -11,6 +11,7 @@
 from optree import tree_flatten_with_path
 
 from _gettsim.config import SUPPORTED_GROUPINGS
+from _gettsim.functions.policy_function import PolicyFunction
 
 
 class KeyErrorMessage(str):
@@ -274,7 +275,7 @@ def format_errors_and_warnings(text, width=79):
     return formatted_text
 
 
-def get_names_of_arguments_without_defaults(function):
+def get_names_of_arguments_without_defaults(function: PolicyFunction) -> list[str]:
     """Get argument names without defaults.
 
     The detection of argument names also works for partialed functions.
@@ -296,7 +297,13 @@ def get_names_of_arguments_without_defaults(function):
         p for p in parameters if parameters[p].default == parameters[p].empty
     ]
 
-    return argument_names_without_defaults
+    # Add namespace to argument names if not already present
+    qualified_argument_names_without_defaults = [
+        f"{function.module_name}__{p}" if "__" not in p else p
+        for p in argument_names_without_defaults
+    ]
+
+    return qualified_argument_names_without_defaults
 
 
 def remove_group_suffix(col):

src/_gettsim_tests/test_shared.py

@@ -1,13 +1,51 @@
 import pytest
 
+from _gettsim.functions.policy_function import PolicyFunction
 from _gettsim.shared import (
     create_dict_from_list,
+    get_names_of_arguments_without_defaults,
     merge_nested_dicts,
     tree_to_dict_with_qualified_name,
     tree_update,
 )
 
 
+def module1__module2__function_with_local_function_argument(a):
+    """Function with a local function argument."""
+    return a
+
+
+def module1__module2__function_with_global_function_argument(module1__module3__a):
+    """Function with a global function argument."""
+    return module1__module3__a
+
+
+@pytest.mark.parametrize(
+    "function, expected_argument_name",
+    [
+        (
+            PolicyFunction(
+                module1__module2__function_with_local_function_argument,
+                module_name="module1__module2",
+                function_name="function_with_local_function_argument",
+            ),
+            "module1__module2__a",
+        ),
+        (
+            PolicyFunction(
+                module1__module2__function_with_global_function_argument,
+                module_name="module1__module2",
+                function_name="function_with_global_function_argument",
+            ),
+            "module1__module3__a",
+        ),
+    ],
+)
+def test_get_names_of_arguments(function, expected_argument_name):
+    names = get_names_of_arguments_without_defaults(function)
+    assert names == [expected_argument_name]
+
+
 @pytest.mark.parametrize(
     "tree, path, value, expected",
     [