fixes PyCQA#277, most of PyCQA#278, and PyCQA#280

bugbear.py

@@ -616,13 +616,15 @@ def check_for_b024_and_b027(self, node: ast.ClassDef):
         """Check for inheritance from abstract classes in abc and lack of
         any methods decorated with abstract*"""
 
-        def is_abc_class(value):
+        def is_abc_class(value, name="ABC"):
+            # class foo(metaclass = [abc.]ABCMeta)
             if isinstance(value, ast.keyword):
-                return value.arg == "metaclass" and is_abc_class(value.value)
-            abc_names = ("ABC", "ABCMeta")
-            return (isinstance(value, ast.Name) and value.id in abc_names) or (
+                return value.arg == "metaclass" and is_abc_class(value.value, "ABCMeta")
+            # class foo(ABC)
+            # class foo(abc.ABC)
+            return (isinstance(value, ast.Name) and value.id == name) or (
                 isinstance(value, ast.Attribute)
-                and value.attr in abc_names
+                and value.attr == name
                 and isinstance(value.value, ast.Name)
                 and value.value.id == "abc"
             )
@@ -647,6 +649,11 @@ def empty_body(body) -> bool:
                 for stmt in body
             )
 
+        # don't check multiple inheritance
+        # https://github.com/PyCQA/flake8-bugbear/issues/277
+        if len(node.bases) + len(node.keywords) > 1:
+            return
+
         # only check abstract classes
         if not any(map(is_abc_class, (*node.bases, *node.keywords))):
             return
@@ -666,7 +673,7 @@ def empty_body(body) -> bool:
 
             if not has_abstract_decorator and empty_body(stmt.body):
                 self.errors.append(
-                    B025(stmt.lineno, stmt.col_offset, vars=(stmt.name,))
+                    B027(stmt.lineno, stmt.col_offset, vars=(stmt.name,))
                 )
 
         if not has_abstract_method:

tests/b024.py

@@ -81,11 +81,32 @@ def method(self):
         foo()
 
 
-class multi_super_1(notabc.ABC, abc.ABCMeta):  # error
+class multi_super_1(notabc.ABC, abc.ABCMeta):  # safe
     def method(self):
         foo()
 
 
-class multi_super_2(notabc.ABC, metaclass=abc.ABCMeta):  # error
+class multi_super_2(notabc.ABC, metaclass=abc.ABCMeta):  # safe
+    def method(self):
+        foo()
+
+
+class non_keyword_abcmeta_1(ABCMeta):  # safe
+    def method(self):
+        foo()
+
+
+class non_keyword_abcmeta_2(abc.ABCMeta):  # safe
+    def method(self):
+        foo()
+
+
+# very invalid code, but that's up to mypy et al to check
+class keyword_abc_1(metaclass=ABC):  # safe
+    def method(self):
+        foo()
+
+
+class keyword_abc_2(metaclass=abc.ABC):  # safe
     def method(self):
         foo()

tests/test_bugbear.py

@@ -364,8 +364,6 @@ def test_b024(self):
             B024(58, 0, vars=("MetaBase_1",)),
             B024(69, 0, vars=("abc_Base_1",)),
             B024(74, 0, vars=("abc_Base_2",)),
-            B024(84, 0, vars=("multi_super_1",)),
-            B024(89, 0, vars=("multi_super_2",)),
         )
         self.assertEqual(errors, expected)
 
@@ -401,15 +399,15 @@ def test_b026(self):
         )
 
     def test_b027(self):
-        filename = Path(__file__).absolute().parent / "b025.py"
+        filename = Path(__file__).absolute().parent / "b027.py"
         bbc = BugBearChecker(filename=str(filename))
         errors = list(bbc.run())
         expected = self.errors(
-            B025(13, 4, vars=("empty_1",)),
-            B025(16, 4, vars=("empty_2",)),
-            B025(19, 4, vars=("empty_3",)),
-            B025(23, 4, vars=("empty_4",)),
-            B025(31, 4, vars=("empty_5",)),
+            B027(13, 4, vars=("empty_1",)),
+            B027(16, 4, vars=("empty_2",)),
+            B027(19, 4, vars=("empty_3",)),
+            B027(23, 4, vars=("empty_4",)),
+            B027(31, 4, vars=("empty_5",)),
         )
         self.assertEqual(errors, expected)