ParamSpecs upper bounds should be a Parameters object and not an actual object

mypy/join.py

@@ -97,7 +97,7 @@ def join_instances(self, t: Instance, s: Instance) -> ProperType:
                 else:
                     # ParamSpec type variables behave the same, independent of variance
                     if not is_equivalent(ta, sa):
-                        return get_proper_type(type_var.upper_bound)
+                        return object_from_instance(t)
                     new_type = join_types(ta, sa, self)
                 assert new_type is not None
                 args.append(new_type)

mypy/semanal.py

@@ -4183,9 +4183,13 @@ def process_paramspec_declaration(self, s: AssignmentStmt) -> bool:
         # on the lines of process_typevar_parameters
 
         if not call.analyzed:
-            paramspec_var = ParamSpecExpr(
-                name, self.qualified_name(name), self.object_type(), INVARIANT
+            parameters = Parameters(
+                arg_types=[self.object_type(), self.object_type()],
+                arg_kinds=[ARG_STAR, ARG_STAR2],
+                arg_names=[None, None],
+                is_ellipsis_args=True,
             )
+            paramspec_var = ParamSpecExpr(name, self.qualified_name(name), parameters, INVARIANT)
             paramspec_var.line = call.line
             call.analyzed = paramspec_var
         else:

mypy/types.py

@@ -704,13 +704,14 @@ def copy_modified(
         id: Bogus[TypeVarId | int] = _dummy,
         flavor: int = _dummy_int,
         prefix: Bogus[Parameters] = _dummy,
+        upper_bound: Bogus[Type] = _dummy,
     ) -> ParamSpecType:
         return ParamSpecType(
             self.name,
             self.fullname,
             id if id is not _dummy else self.id,
             flavor if flavor != _dummy_int else self.flavor,
-            self.upper_bound,
+            upper_bound if upper_bound is not _dummy else self.upper_bound,
             line=self.line,
             column=self.column,
             prefix=prefix if prefix is not _dummy else self.prefix,
@@ -1991,7 +1992,18 @@ def param_spec(self) -> ParamSpecType | None:
             # TODO: confirm that all arg kinds are positional
             prefix = Parameters(self.arg_types[:-2], self.arg_kinds[:-2], self.arg_names[:-2])
 
-        return arg_type.copy_modified(flavor=ParamSpecFlavor.BARE, prefix=prefix)
+        # TODO: should this take in `object`s? Or use prefix + *Any **Any as upper bound?
+        any_type = AnyType(TypeOfAny.special_form)
+        return arg_type.copy_modified(
+            flavor=ParamSpecFlavor.BARE,
+            prefix=prefix,
+            upper_bound=Parameters(
+                arg_types=[any_type, any_type],
+                arg_kinds=[ARG_STAR, ARG_STAR2],
+                arg_names=[None, None],
+                is_ellipsis_args=True,
+            ),
+        )
 
     def expand_param_spec(
         self, c: CallableType | Parameters, no_prefix: bool = False

test-data/unit/semanal-types.test

@@ -1549,7 +1549,8 @@ MypyFile:1(
   ImportFrom:1(typing, [ParamSpec])
   AssignmentStmt:2(
     NameExpr(P* [__main__.P])
-    ParamSpecExpr:2()))
+    ParamSpecExpr:2(
+      UpperBound(...))))
 
 [case testTypeVarTuple]
 from typing_extensions import TypeVarTuple