PY-27656 PY-27604 Exclude ancestors of metaclasses from class hierarchy

in case this relationship was created implicitly by inheriting an
instance of metaclass.

It also fixes warnings about the first parameter of SQLAlchemy model
methods being named "self" instead of "cls" since we no longer consider
these classes descendants of "type".

python/src/com/jetbrains/python/psi/impl/PyClassImpl.java

@@ -427,7 +427,22 @@ public class PyClassImpl extends PyBaseElementImpl<PyClassStub> implements PyCla
       final List<List<PyClassLikeType>> lines = new ArrayList<>();
       for (PyClassLikeType base : bases) {
         if (base != null) {
-          final List<PyClassLikeType> baseClassMRO = mroLinearize(base, true, context, cache);
+          // Don't include ancestors of a metaclass instance
+          final List<PyClassLikeType> baseClassMRO;
+          if (base.isDefinition()) {
+            baseClassMRO = mroLinearize(base, true, context, cache);
+          }
+          else {
+            List<PyClassLikeType> metaclassInstanceMro = new ArrayList<>();
+            metaclassInstanceMro.add(base);
+            if (base instanceof PyClassType) {
+              final PyClassImpl pyClass = as(((PyClassType)base).getPyClass(), PyClassImpl.class);
+              if (pyClass != null) {
+                ContainerUtil.addIfNotNull(metaclassInstanceMro, pyClass.getImplicitSuper(context));
+              }
+            }
+            baseClassMRO = metaclassInstanceMro;
+          }
           if (!baseClassMRO.isEmpty()) {
             // mroMerge() updates passed MRO lists internally
             lines.add(new LinkedList<>(baseClassMRO));

python/testData/codeInsight/classMRO/DirectlyInstantiatedMetaclassAncestor.py

@@ -0,0 +1,13 @@
+class MetaBase(type):
+    pass
+
+
+class Meta(MetaBase):
+    pass
+
+
+Base = Meta('Base', (), {})
+
+
+class MyClass(Base):
+    pass

python/testSrc/com/jetbrains/python/codeInsight/PyClassMROTest.java

@@ -125,6 +125,11 @@ public class PyClassMROTest extends PyTestCase {
     assertMRO(getClass("MyClass"), "Base", "object");
   }
 
+  // PY-27656
+  public void testDirectlyInstantiatedMetaclassAncestor() {
+    runWithLanguageLevel(LanguageLevel.PYTHON30, () -> assertMRO(getClass("MyClass"), "Meta", "object"));
+  }
+
   // PY-20026
   public void testUnresolvedMetaClassAncestors() {
     runWithLanguageLevel(LanguageLevel.PYTHON30, () -> assertMRO(getClass("CompositeFieldMeta"), "type", "object"));