Fix a false negative for abstract-method when an abstract class is the direct ancestor of a derived class.

Closes pylint-dev#9979

Author: mbyrnepr2

doc/data/messages/a/abstract-method/bad/abstract_method.py

@@ -1,7 +1,7 @@
 import abc
 
 
-class WildAnimal:
+class WildAnimal(abc.ABC):
     @abc.abstractmethod
     def make_sound(self):
         pass

doc/data/messages/a/abstract-method/good/abstract_method.py

@@ -1,7 +1,7 @@
 import abc
 
 
-class WildAnimal:
+class WildAnimal(abc.ABC):
     @abc.abstractmethod
     def make_sound(self):
         pass

doc/whatsnew/fragments/9979.false_negative

@@ -0,0 +1,3 @@
+Fix a false negative for ``abstract-method`` when an abstract class is the direct ancestor of a derived class.
+
+Closes #9979

pylint/checkers/utils.py

@@ -1166,8 +1166,11 @@ def class_is_abstract(node: nodes.ClassDef) -> bool:
         if meta.name == "ABCMeta" and meta.root().name in ABC_MODULES:
             return True
 
-    for ancestor in node.ancestors():
-        if ancestor.name == "ABC" and ancestor.root().name in ABC_MODULES:
+    for ancestor in node.ancestors(recurs=False):
+        if (
+            ancestor.name == "ABC"
+            and ancestor.root().name in ABC_MODULES
+        ):
             # abc.ABC inheritance
             return True
 

tests/functional/a/abstract/abstract_method.py

@@ -105,3 +105,18 @@ class GoodComplexMRO(Container, Iterator, Sizable, Hashable):
 # +1: [abstract-method, abstract-method, abstract-method]
 class BadComplexMro(Container, Iterator, AbstractSizable):
     pass
+
+
+class Base(abc.ABC):
+    @abc.abstractmethod
+    def do_something(self):
+        pass
+
+
+# +1: [abstract-method]
+class Derived(Base):
+    """ Test that a class derived from an abstract class correctly triggers
+        `abstract-method`.
+    """
+    def do_something_else(self):
+        pass

tests/functional/a/abstract/abstract_method.txt

@@ -14,3 +14,4 @@ abstract-method:87:0:87:14:Iterator:Method '__len__' is abstract in class 'Struc
 abstract-method:106:0:106:19:BadComplexMro:Method '__hash__' is abstract in class 'Structure' but is not overridden in child class 'BadComplexMro':INFERENCE
 abstract-method:106:0:106:19:BadComplexMro:Method '__len__' is abstract in class 'AbstractSizable' but is not overridden in child class 'BadComplexMro':INFERENCE
 abstract-method:106:0:106:19:BadComplexMro:Method 'length' is abstract in class 'AbstractSizable' but is not overridden in child class 'BadComplexMro':INFERENCE
+abstract-method:117:0:117:13:Derived:Method 'do_something' is abstract in class 'Base' but is not overridden in child class 'Derived':INFERENCE