keep using mode.string_storage as default for NA variant + more xfails

Author: jorisvandenbossche

pandas/core/arrays/string_.py

@@ -129,7 +129,7 @@ def __init__(
     ) -> None:
         # infer defaults
         if storage is None:
-            if using_string_dtype():
+            if using_string_dtype() and na_value is not libmissing.NA:
                 storage = "pyarrow"
             else:
                 storage = get_option("mode.string_storage")

pandas/tests/io/parser/test_index_col.py

@@ -9,6 +9,8 @@
 import numpy as np
 import pytest
 
+from pandas._config import using_string_dtype
+
 from pandas import (
     DataFrame,
     Index,
@@ -343,6 +345,7 @@ def test_infer_types_boolean_sum(all_parsers):
     tm.assert_frame_equal(result, expected, check_index_type=False)
 
 
+@pytest.mark.xfail(using_string_dtype(), reason="TODO(infer_string)", strict=False)
 @pytest.mark.parametrize("dtype, val", [(object, "01"), ("int64", 1)])
 def test_specify_dtype_for_index_col(all_parsers, dtype, val, request):
     # GH#9435