Fix PyCQA#293, B024 now skips classes with class attribute declarations

bugbear.py

@@ -640,6 +640,10 @@ def is_abstract_decorator(expr):
                 map(is_abstract_decorator, stmt.decorator_list)
             ):
                 return
+            # https://github.com/PyCQA/flake8-bugbear/issues/293
+            # Ignore abc's that declares a class attribute that must be set
+            if isinstance(stmt, (ast.AnnAssign, ast.Assign)):
+                return
 
         self.errors.append(B024(node.lineno, node.col_offset, vars=(node.name,)))
 

tests/b024.py

@@ -89,3 +89,20 @@ def method(self):
 class multi_super_2(notabc.ABC, metaclass=abc.ABCMeta):  # error
     def method(self):
         ...
+
+
+class abc_set_class_variable_1(ABC):  # safe
+    foo: int
+
+
+class abc_set_class_variable_2(ABC):  # safe
+    foo = 2
+
+
+class abc_set_class_variable_3(ABC):  # safe
+    foo: int = 2
+
+
+# this doesn't actually declare a class variable, it's just an expression
+class abc_set_class_variable_4(ABC):  # error
+    foo

tests/test_bugbear.py

@@ -365,6 +365,7 @@ def test_b024(self):
             B024(74, 0, vars=("abc_Base_2",)),
             B024(84, 0, vars=("multi_super_1",)),
             B024(89, 0, vars=("multi_super_2",)),
+            B024(107, 0, vars=("abc_set_class_variable_4",)),
         )
         self.assertEqual(errors, expected)