[Backport maintenance/2.17.x] Fix crash in invalid-metaclass check (#8700)

* Fix crash in `invalid-metaclass` check (#8699)

(cherry picked from commit 7a562dd)

* Remove test case for inconsistent-mro

This was added only to cover the second exception
type that needs to be handled here; but backporting it to
branches supporting 3.7 would require rewriting the test case.

---------

Co-authored-by: Jacob Walls <[email protected]>

Author: github-actions[bot]

doc/whatsnew/fragments/8698.bugfix

@@ -0,0 +1,3 @@
+Fix crash in ``invalid-metaclass`` check when a metaclass had duplicate bases.
+
+Closes #8698

pylint/checkers/typecheck.py

@@ -745,7 +745,10 @@ def _no_context_variadic(
 
 
 def _is_invalid_metaclass(metaclass: nodes.ClassDef) -> bool:
-    mro = metaclass.mro()
+    try:
+        mro = metaclass.mro()
+    except (astroid.DuplicateBasesError, astroid.InconsistentMroError):
+        return True
     return not any(is_builtin_object(cls) and cls.name == "type" for cls in mro)
 
 

tests/functional/i/invalid/invalid_metaclass.py

@@ -68,3 +68,11 @@ class Invalid(metaclass=invalid_metaclass_1):  # [invalid-metaclass]
 
 class InvalidSecond(metaclass=invalid_metaclass_2):  # [invalid-metaclass]
     pass
+
+
+class MetaclassWithInvalidMRO(type(object), type(object)):  # [duplicate-bases]
+    pass
+
+
+class FifthInvalid(metaclass=MetaclassWithInvalidMRO):  # [invalid-metaclass]
+    pass

tests/functional/i/invalid/invalid_metaclass.txt

@@ -4,3 +4,5 @@ invalid-metaclass:49:0:49:18:ThirdInvalid:Invalid metaclass '2' used:UNDEFINED
 invalid-metaclass:53:0:53:19:FourthInvalid:Invalid metaclass 'Instance of invalid_metaclass.InvalidAsMetaclass' used:UNDEFINED
 invalid-metaclass:65:0:65:13:Invalid:Invalid metaclass 'int' used:UNDEFINED
 invalid-metaclass:69:0:69:19:InvalidSecond:Invalid metaclass '1' used:UNDEFINED
+duplicate-bases:73:0:73:29:MetaclassWithInvalidMRO:Duplicate bases for class 'MetaclassWithInvalidMRO':UNDEFINED
+invalid-metaclass:77:0:77:18:FifthInvalid:Invalid metaclass 'MetaclassWithInvalidMRO' used:UNDEFINED