Fix crash in ExplicitNamespacePackageFinder (pylint-dev#1714)

* Add skip if no `six`
* `urllib3` does appear to be required
* Check `submodule_search_locations`

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

ChangeLog

@@ -12,6 +12,10 @@ What's New in astroid 2.12.3?
 =============================
 Release date: TBA
 
+* Fixed crash in ``ExplicitNamespacePackageFinder`` involving ``_SixMetaPathImporter``.
+
+  Closes #1708
+
 * Fix unhandled `FutureWarning` from pandas import in cython modules
 
   Closes #1717

astroid/interpreter/_import/util.py

@@ -72,7 +72,8 @@ def is_namespace(modname: str) -> bool:
         if found_spec and found_spec.submodule_search_locations:
             last_submodule_search_locations = found_spec.submodule_search_locations
 
-    if found_spec is None:
-        return False
-
-    return found_spec.origin is None
+    return (
+        found_spec is not None
+        and found_spec.submodule_search_locations is not None
+        and found_spec.origin is None
+    )

requirements_test_brain.txt

@@ -7,3 +7,4 @@ PyQt6
 types-python-dateutil
 six
 types-six
+urllib3

tests/unittest_modutils.py

@@ -17,6 +17,7 @@
 from xml import etree
 from xml.etree import ElementTree
 
+import pytest
 from pytest import CaptureFixture, LogCaptureFixture
 
 import astroid
@@ -25,6 +26,13 @@
 
 from . import resources
 
+try:
+    import urllib3  # pylint: disable=unused-import
+
+    HAS_URLLIB3 = True
+except ImportError:
+    HAS_URLLIB3 = False
+
 
 def _get_file_from_object(obj) -> str:
     return modutils._path_from_filename(obj.__file__)
@@ -439,5 +447,14 @@ def test_is_module_name_part_of_extension_package_whitelist_success(self) -> Non
         )
 
 
+@pytest.mark.skipif(not HAS_URLLIB3, reason="This test requires urllib3.")
+def test_file_info_from_modpath__SixMetaPathImporter() -> None:
+    pytest.raises(
+        ImportError,
+        modutils.file_info_from_modpath,
+        ["urllib3.packages.six.moves.http_client"],
+    )
+
+
 if __name__ == "__main__":
     unittest.main()