Follow PEP 673 instead of PEP 484 when dealing with implicit self

Author: davfsa

mypy/semanal.py

@@ -972,11 +972,7 @@ def prepare_method_signature(self, func: FuncDef, info: TypeInfo, has_self_type:
             elif isinstance(functype, CallableType):
                 self_type = get_proper_type(functype.arg_types[0])
                 if isinstance(self_type, AnyType):
-                    if has_self_type:
-                        assert self.type is not None and self.type.self_type is not None
-                        leading_type: Type = self.type.self_type
-                    else:
-                        leading_type = fill_typevars(info)
+                    leading_type = info.self_type if info.self_type else fill_typevars(info)
                     if func.is_class or func.name == "__new__":
                         leading_type = self.class_type(leading_type)
                     func.type = replace_implicit_first_type(functype, leading_type)

test-data/unit/check-selftype.test

@@ -1692,9 +1692,8 @@ class C:
         return self
     def baz(self: Self) -> None:
         self.x = self
-    def bad(self) -> None:
-        # This is unfortunate, but required by PEP 484
-        self.x = self  # E: Incompatible types in assignment (expression has type "C", variable has type "Self")
+    def eggs(self) -> None:
+        self.x = self
 
 [case testTypingSelfClashInBodies]
 from typing import Self, TypeVar