From e17862654fc0585e63f5ab6785eab23787e91e9b Mon Sep 17 00:00:00 2001
From: doranid <ddandd@gmail.com>
Date: Sun, 1 Aug 2021 22:04:46 +0300
Subject: [PATCH] Don't calculate slots when MRO parsing fails. (#1089)

* Don't calculate slots when MRO parsing fails.

* Added changelog entry.

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>
---
 ChangeLog                      |  4 ++++
 astroid/scoped_nodes.py        | 16 +++++++++++++---
 tests/unittest_scoped_nodes.py | 11 +++++++++++
 3 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index e65a4c4104..ca355f1b39 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -44,6 +44,10 @@ Release date: 2021-07-19
 
 * Added ``If.is_sys_guard`` and ``If.is_typing_guard`` helper methods
 
+* Fix handling of classes with duplicated bases with the same name
+
+  Closes PyCQA/astroid#1088
+
 * Fix a bad inferenece type for yield values inside of a derived class.
 
   Closes PyCQA/astroid#1090
diff --git a/astroid/scoped_nodes.py b/astroid/scoped_nodes.py
index c7c287798c..910d303564 100644
--- a/astroid/scoped_nodes.py
+++ b/astroid/scoped_nodes.py
@@ -42,6 +42,7 @@
 import builtins
 import io
 import itertools
+import typing
 from typing import List, Optional
 
 from astroid import bases
@@ -2906,9 +2907,11 @@ def slots(self):
         :rtype: list(str) or None
         """
 
-        def grouped_slots():
+        def grouped_slots(
+            mro: List["ClassDef"],
+        ) -> typing.Iterator[Optional[node_classes.NodeNG]]:
             # Not interested in object, since it can't have slots.
-            for cls in self.mro()[:-1]:
+            for cls in mro[:-1]:
                 try:
                     cls_slots = cls._slots()
                 except NotImplementedError:
@@ -2923,7 +2926,14 @@ def grouped_slots():
                 "The concept of slots is undefined for old-style classes."
             )
 
-        slots = list(grouped_slots())
+        try:
+            mro = self.mro()
+        except MroError as e:
+            raise NotImplementedError(
+                "Cannot get slots while parsing mro fails."
+            ) from e
+
+        slots = list(grouped_slots(mro))
         if not all(slot is not None for slot in slots):
             return None
 
diff --git a/tests/unittest_scoped_nodes.py b/tests/unittest_scoped_nodes.py
index 8fd890d163..56e1ed2996 100644
--- a/tests/unittest_scoped_nodes.py
+++ b/tests/unittest_scoped_nodes.py
@@ -2230,5 +2230,16 @@ class C(B[str]): pass
     ]
 
 
+def test_slots_duplicate_bases_issue_1089():
+    astroid = builder.parse(
+        """
+            class First(object, object): #@
+                pass
+        """
+    )
+    with pytest.raises(NotImplementedError):
+        astroid["First"].slots()
+
+
 if __name__ == "__main__":
     unittest.main()