SubtypeVisitor: treat ParamSpec as if it was a covariant TypeVar

Author: Akuli

mypy/subtypes.py

@@ -290,6 +290,9 @@ def visit_instance(self, left: Instance) -> bool:
                     if isinstance(tvar, TypeVarType):
                         if not self.check_type_parameter(lefta, righta, tvar.variance):
                             nominal = False
+                    elif isinstance(tvar, ParamSpecType):
+                        if not self.check_type_parameter(lefta, righta, COVARIANT):
+                            nominal = False
                     else:
                         if not self.check_type_parameter(lefta, righta, COVARIANT):
                             nominal = False