Fix join of Tuple and NamedTuple

Author: pkch

mypy/subtypes.py

@@ -143,10 +143,15 @@ def visit_instance(self, left: Instance) -> bool:
             rname = right.type.fullname()
             if not left.type.has_base(rname) and rname != 'builtins.object':
                 return False
-
             # Map left type to corresponding right instances.
             t = map_instance_to_supertype(left, right.type)
-
+            # Check that one of the types does not have type args or
+            # the number of type args is the same and
+            # each left type arg is acceptable in place of the matching right one
+            if not t.args or not right.args:
+                return True
+            if len(t.args) != len(right.args):
+                return False
             return all(self.check_type_parameter(lefta, righta, tvar.variance)
                        for lefta, righta, tvar in
                        zip(t.args, right.args, right.type.defn.type_vars))

mypy/types.py

@@ -1428,7 +1428,7 @@ def visit_tuple_type(self, t: TupleType) -> str:
         s = self.list_str(t.items)
         if t.fallback and t.fallback.type:
             fallback_name = t.fallback.type.fullname()
-            if fallback_name != 'builtins.tuple':
+            if fallback_name not in ('builtins.tuple', 'builtins.object'):
                 return 'Tuple[{}, fallback={}]'.format(s, t.fallback.accept(self))
         return 'Tuple[{}]'.format(s)