Set envvar based on visited files

Author: hasier

mypy/config_parser.py

@@ -365,9 +365,9 @@ def _parse_and_extend_config_file(
         return None
     visited.add(abs_file_read)
 
-    if not os.environ.get("MYPY_CONFIG_FILE_DIR"):
-        # set it only if unset to allow for path variable expansions when parsing below,
-        # so recursive calls for config extend references won't overwrite it
+    if len(visited) == 1:
+        # set it only after the first config file is visited to allow for path variable expansions
+        # when parsing below, so recursive calls for config extend references won't overwrite it
         os.environ["MYPY_CONFIG_FILE_DIR"] = os.path.dirname(abs_file_read)
 
     mypy_updates: dict[str, object] = {}

mypy/test/test_config_parser.py

@@ -174,6 +174,7 @@ def set_strict_flags() -> None:
                 assert strict_option_set is True
                 assert options.ignore_missing_imports_per_module is True
                 assert options.config_file == str(pyproject.name)
+                assert os.environ["MYPY_CONFIG_FILE_DIR"] == str(pyproject.parent)
 
                 assert options.per_module_options["c"] == {
                     "disable_error_code": [],