Fix deserialisation of ParamSpecType (#10923)

Co-authored-by: hauntsaninja <>

Author: hauntsaninja

mypy/types.py

@@ -1252,21 +1252,21 @@ def serialize(self) -> JsonDict:
     def deserialize(cls, data: JsonDict) -> 'CallableType':
         assert data['.class'] == 'CallableType'
         # TODO: Set definition to the containing SymbolNode?
-        return CallableType([deserialize_type(t) for t in data['arg_types']],
-                            [ArgKind(x) for x in data['arg_kinds']],
-                            data['arg_names'],
-                            deserialize_type(data['ret_type']),
-                            Instance.deserialize(data['fallback']),
-                            name=data['name'],
-                            variables=[TypeVarType.deserialize(v) for v in data['variables']],
-                            is_ellipsis_args=data['is_ellipsis_args'],
-                            implicit=data['implicit'],
-                            bound_args=[(None if t is None else deserialize_type(t))
-                                        for t in data['bound_args']],
-                            def_extras=data['def_extras'],
-                            type_guard=(deserialize_type(data['type_guard'])
-                                        if data['type_guard'] is not None else None),
-                            )
+        return CallableType(
+            [deserialize_type(t) for t in data['arg_types']],
+            [ArgKind(x) for x in data['arg_kinds']],
+            data['arg_names'],
+            deserialize_type(data['ret_type']),
+            Instance.deserialize(data['fallback']),
+            name=data['name'],
+            variables=[cast(TypeVarLikeType, deserialize_type(v)) for v in data['variables']],
+            is_ellipsis_args=data['is_ellipsis_args'],
+            implicit=data['implicit'],
+            bound_args=[(None if t is None else deserialize_type(t)) for t in data['bound_args']],
+            def_extras=data['def_extras'],
+            type_guard=(deserialize_type(data['type_guard'])
+                        if data['type_guard'] is not None else None),
+        )
 
 
 class Overloaded(FunctionLike):