From 935e9ffc8bba0624678447af97cd455788a98f27 Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <ilevkivskyi@dropbox.com>
Date: Thu, 5 Sep 2019 18:49:23 +0100
Subject: [PATCH 1/2] Bind self correctly when mapping class methods from
 supertype

---
 mypy/checker.py                    |  8 ++++-
 test-data/unit/check-generics.test | 49 ++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/mypy/checker.py b/mypy/checker.py
index 4dabdc6fdfcd..5eb36c81b38f 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -1530,7 +1530,13 @@ def bind_and_map_method(self, sym: SymbolTableNode, typ: FunctionLike,
         """
         if (isinstance(sym.node, (FuncDef, OverloadedFuncDef, Decorator))
                 and not is_static(sym.node)):
-            bound = bind_self(typ, self.scope.active_self_type())
+            if isinstance(sym.node, Decorator):
+                is_class_method = sym.node.func.is_class
+            elif isinstance(sym.node, OverloadedFuncDef):
+                is_class_method = sym.node.is_class
+            else:
+                is_class_method = False
+            bound = bind_self(typ, self.scope.active_self_type(), is_class_method)
         else:
             bound = typ
         return cast(FunctionLike, map_type_from_supertype(bound, sub_info, super_info))
diff --git a/test-data/unit/check-generics.test b/test-data/unit/check-generics.test
index c7866dbbedee..4a3829200f65 100644
--- a/test-data/unit/check-generics.test
+++ b/test-data/unit/check-generics.test
@@ -2062,3 +2062,52 @@ class A:
 x, y = A()
 reveal_type(x)  # N: Revealed type is 'Any'
 reveal_type(y)  # N: Revealed type is 'Any'
+
+[case testSubclassingGenericSelfClassMethod]
+from typing import TypeVar, Type
+
+AT = TypeVar('AT', bound='A')
+
+class A:
+    @classmethod
+    def from_config(cls: Type[AT]) -> AT:
+        ...
+
+class B(A):
+    @classmethod
+    def from_config(cls: Type[B]) -> B:
+        return B()
+[builtins fixtures/classmethod.pyi]
+
+[case testSubclassingGenericSelfClassMethodOptional]
+# flags: --strict-optional
+from typing import TypeVar, Type, Optional
+
+AT = TypeVar('AT', bound='A')
+
+class A:
+    @classmethod
+    def from_config(cls: Type[AT]) -> Optional[AT]:
+        return None
+
+class B(A):
+    @classmethod
+    def from_config(cls: Type[B]) -> Optional[B]:
+        return B()
+[builtins fixtures/classmethod.pyi]
+
+[case testSubclassingGenericSelfClassMethodNonAnnotated]
+from typing import TypeVar, Type
+
+AT = TypeVar('AT', bound='A')
+
+class A:
+    @classmethod
+    def from_config(cls: Type[AT]) -> AT:
+        ...
+
+class B(A):
+    @classmethod
+    def from_config(cls) -> B:
+        return B()
+[builtins fixtures/classmethod.pyi]

From 7de627c514f65272076321a8b99561a031fdbe76 Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <ilevkivskyi@dropbox.com>
Date: Thu, 5 Sep 2019 21:46:51 +0100
Subject: [PATCH 2/2] Address CR

---
 mypy/checker.py | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mypy/checker.py b/mypy/checker.py
index 5eb36c81b38f..b758af4ad5e6 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -1532,10 +1532,8 @@ def bind_and_map_method(self, sym: SymbolTableNode, typ: FunctionLike,
                 and not is_static(sym.node)):
             if isinstance(sym.node, Decorator):
                 is_class_method = sym.node.func.is_class
-            elif isinstance(sym.node, OverloadedFuncDef):
-                is_class_method = sym.node.is_class
             else:
-                is_class_method = False
+                is_class_method = sym.node.is_class
             bound = bind_self(typ, self.scope.active_self_type(), is_class_method)
         else:
             bound = typ