Consider class inheriting abc.ABC as abstract (PY-30789)

python/src/com/jetbrains/python/inspections/PyAbstractClassInspection.java

@@ -60,6 +60,11 @@ public class PyAbstractClassInspection extends PyInspection {
       if (metaClass != null && PyNames.ABC_META_CLASS.equals(metaClass.getName())) {
         return true;
       }
+      for (PyClassLikeType superClassType : pyClass.getSuperClassTypes(myTypeEvalContext)) {
+        if (superClassType != null && "abc.ABC".equals(superClassType.getClassQName())) {
+          return true;
+        }
+      }
       for (PyFunction method : pyClass.getMethods()) {
         if (PyKnownDecoratorUtil.hasAbstractDecorator(method, myTypeEvalContext)) {
           return true;

python/testData/inspections/PyAbstractClassInspection/HiddenForAbstractSubclassWithABCSuperclass/a.py

@@ -0,0 +1,9 @@
+import abc
+
+class A1(abc.ABC):
+    @abc.abstractmethod
+    def m1(self):
+        pass
+
+class A2(A1, abc.ABC):
+    pass

python/testData/inspections/PyAbstractClassInspection/HiddenForAbstractSubclassWithABCSuperclass/abc.py

@@ -0,0 +1,13 @@
+class ABCMeta:
+    pass
+
+
+class ABC(metaclass=ABCMeta):
+    """Helper class that provides a standard way to create an ABC using
+    inheritance.
+    """
+    pass
+
+
+def abstractmethod(foo):
+    pass

python/testSrc/com/jetbrains/python/inspections/PyAbstractClassInspectionTest.java

@@ -34,6 +34,11 @@ public class PyAbstractClassInspectionTest extends PyInspectionTestCase {
     doTest();
   }
 
+  // PY-30789
+  public void testHiddenForAbstractSubclassWithABCSuperclass() {
+    runWithLanguageLevel(LanguageLevel.PYTHON34, this::doMultiFileTest);
+  }
+
   // PY-16776
   public void testNotImplementedOverriddenInParent() {
     doTest();