Protect against `NonDeducibleTypeHierarchy` when calling semi-private `is_subtype`

`astroid.helpers.is_subtype` raises `NonDeducibleTypeHierarchy` when it cannot infer
the base classes of the given types, but that makes sense in its context given that
the method is mostly used to inform the inference process about the hierarchy of classes.
Doesn't make that much sense for ``pylint`` itself, which is why we're handling the
exception here, rather than in ``astroid``

Close PyCQA/astroid#644

1 files changed, 6 insertions, 2 deletions

diff --git a/pylint/checkers/utils.py b/pylint/checkers/utils.py
index 3cc292115..b4129389f 100644
--- a/pylint/checkers/utils.py
+++ b/pylint/checkers/utils.py
@@ -40,6 +40,7 @@ from typing import Optional, Iterable, Tuple, Callable, Set, Union, Match, Dict,
 import _string  # pylint: disable=wrong-import-position, wrong-import-order
 
 import astroid
+from astroid.exceptions import _NonDeducibleTypeHierarchy
 from astroid import bases as _bases
 from astroid import scoped_nodes
 
@@ -1202,6 +1203,9 @@ def is_subclass_of(child: astroid.ClassDef, parent: astroid.ClassDef) -> bool:
         return False
 
     for ancestor in child.ancestors():
-        if astroid.helpers.is_subtype(ancestor, parent):
-            return True
+        try:
+            if astroid.helpers.is_subtype(ancestor, parent):
+                return True
+        except _NonDeducibleTypeHierarchy:
+            continue
     return False