You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: func_resolver.go
    path of file: ./repos/cockroach/pkg/ccl/changefeedccl/cdceval
    
    the code of the file until where you have to start completion: // Copyright 2022 The Cockroach Authors.
//
// Licensed as a CockroachDB Enterprise file under the Cockroach Community
// License (the "License"); you may not use this file except in compliance with
// the License. You may obtain a copy of the License at
//
//     https://github.com/cockroachdb/cockroach/blob/master/licenses/CCL.txt

packa
    
func checkOverloadSupported(fnName string, overload *tree.Overload) error {
	switch overload.Class {
	case tree.AggregateClass, tree.GeneratorClass, tree.WindowClass:
		return pgerror.Newf(pgcode.UndefinedFunction, "aggregate, generator, or window function %q unsupported by CDC", fnName)
	}
	if overload.Volatility == volatility.Volatile {
		return pgerror.Newf(pgcode.UndefinedFunction, "volatile functions %q unsupported by CDC", fnName)
	}
	return nil
}