Move __getattr__ None check from normalize_mark_list to get_unpacked_marks

Per reviewer feedback, move the check for module-level __getattr__
returning None to get_unpacked_marks() (the helper that fetches the
mark list) instead of normalize_mark_list(). Also change from raising
a TypeError to emitting a PytestCollectionWarning, so the module can
still be collected normally.

Author: veeceey

changelog/8265.improvement.rst

@@ -1,5 +1,4 @@
-Improved error message when a module-level ``__getattr__`` fails to raise ``AttributeError`` for missing attributes.
+Emit a ``PytestCollectionWarning`` when a module-level ``__getattr__`` returns ``None`` for ``pytestmark`` instead of raising ``AttributeError``.
 
-When a module defines a custom ``__getattr__`` that returns ``None`` instead of raising ``AttributeError``,
-pytest now provides a more helpful error message explaining the likely cause and suggesting the fix,
-rather than the cryptic "got None instead of Mark" message.
+Previously this caused a cryptic ``TypeError: got None instead of Mark`` error.
+Now pytest issues a helpful warning and continues collecting the module normally.

src/_pytest/mark/structures.py

@@ -30,6 +30,7 @@
 from _pytest.outcomes import fail
 from _pytest.raises import AbstractRaises
 from _pytest.scope import _ScopeName
+from _pytest.warning_types import PytestCollectionWarning
 from _pytest.warning_types import PytestUnknownMarkWarning
 
 
@@ -443,7 +444,18 @@ def get_unpacked_marks(
                 mark_list.append(item)
     else:
         mark_attribute = getattr(obj, "pytestmark", [])
-        if isinstance(mark_attribute, list):
+        if mark_attribute is None:
+            warnings.warn(
+                "Module defines a `__getattr__` which returns None for "
+                "'pytestmark' instead of raising AttributeError. "
+                "Make sure `__getattr__` raises AttributeError for "
+                "attributes it does not provide. "
+                "See https://github.com/pytest-dev/pytest/issues/8265",
+                PytestCollectionWarning,
+                stacklevel=2,
+            )
+            mark_list = []
+        elif isinstance(mark_attribute, list):
             mark_list = mark_attribute
         else:
             mark_list = [mark_attribute]
@@ -463,15 +475,6 @@ def normalize_mark_list(
     for mark in mark_list:
         mark_obj = getattr(mark, "mark", mark)
         if not isinstance(mark_obj, Mark):
-            # Provide a helpful error message for a common mistake:
-            # a module-level __getattr__ that doesn't raise AttributeError
-            if mark_obj is None:
-                raise TypeError(
-                    "got None instead of Mark - "
-                    "this is likely caused by a module-level __getattr__ "
-                    "that does not raise AttributeError for missing attributes. "
-                    "Make sure __getattr__ raises AttributeError when the attribute is not found."
-                )
             raise TypeError(f"got {mark_obj!r} instead of Mark")
         yield mark_obj
 

testing/test_mark.py

@@ -1348,8 +1348,8 @@ def foo():
 
 def test_module_getattr_without_attributeerror(pytester: Pytester) -> None:
     """
-    Test that a helpful error message is provided when a module-level
-    __getattr__ fails to raise AttributeError.
+    Test that a helpful warning is emitted when a module-level
+    __getattr__ returns None instead of raising AttributeError.
 
     Regression test for https://github.com/pytest-dev/pytest/issues/8265
     """
@@ -1363,12 +1363,12 @@ def test_something():
             assert True
         """
     )
-    result = pytester.runpytest()
+    result = pytester.runpytest("-W", "always::pytest.PytestCollectionWarning")
     result.stdout.fnmatch_lines(
         [
-            "*TypeError*got None instead of Mark*",
-            "*module-level __getattr__*",
-            "*AttributeError*",
+            "*PytestCollectionWarning*__getattr__*returns None*AttributeError*",
         ]
     )
-    assert result.ret != 0
+    # The module is buggy (__getattr__ returns None for all attributes),
+    # so no tests are collected, but pytest should NOT crash with a TypeError.
+    assert result.ret != ExitCode.INTERNAL_ERROR