Implement a basic meet for overloaded types

mypy/meet.py

@@ -5,7 +5,7 @@
 from mypy.types import (
     Type, AnyType, TypeVisitor, UnboundType, NoneTyp, TypeVarType, Instance, CallableType,
     TupleType, TypedDictType, ErasedType, UnionType, PartialType, DeletedType,
-    UninhabitedType, TypeType, TypeOfAny
+    UninhabitedType, TypeType, TypeOfAny, Overloaded, FunctionLike
 )
 from mypy.subtypes import is_equivalent, is_subtype, is_protocol_implementation
 
@@ -314,6 +314,21 @@ def visit_callable_type(self, t: CallableType) -> Type:
         else:
             return self.default(self.s)
 
+    def visit_overloaded(self, t: Overloaded) -> Type:
+        # TODO: Implement a better algorithm that covers at least the same cases
+        # as TypeJoinVisitor.visit_overloaded().
+        s = self.s
+        if isinstance(s, FunctionLike):
+            if s.items() == t.items():
+                return Overloaded(t.items())
+            elif is_subtype(s, t):
+                return s
+            elif is_subtype(t, s):
+                return t
+            else:
+                return meet_types(t.fallback, s.fallback)
+        return meet_types(t.fallback, s)
+
     def visit_tuple_type(self, t: TupleType) -> Type:
         if isinstance(self.s, TupleType) and self.s.length() == t.length():
             items = []  # type: List[Type]

test-data/unit/check-overloading.test

@@ -4078,3 +4078,25 @@ g(3)  # E: No overload variant of "g" matches argument type "int" \
       # N:     def g(x: A) -> None \
       # N:     def g(x: B) -> None \
       # N:     def g(x: C) -> None
+
+[case testOverloadedInIter]
+from lib import f, g
+
+for fun in [f, g]:
+    reveal_type(fun)  # E: Revealed type is 'Overload(def (x: builtins.int) -> builtins.str, def (x: builtins.str) -> builtins.int)'
+[file lib.pyi]
+from typing import overload
+
+@overload
+def f(x: int) -> str: ...
+@overload
+def f(x: str) -> int: ...
+
+@overload
+def g(x: int) -> str: ...
+@overload
+def g(x: str) -> int: ...
+
+[builtins fixtures/list.pyi]
+[typing fixtures/typing-full.pyi]
+[out]