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: decode.go
    path of file: ./repos/faas-netes/vendor/github.com/gogo/protobuf/proto
    
    the code of the file until where you have to start completion: // Go support for Protocol Buffers - Google's data interchange format
//
// Copyright 2010 The Go Authors.  All rights reserved.
// https://github.com/golang/pr
    
func UnmarshalMerge(buf []byte, pb Message) error {
	if u, ok := pb.(newUnmarshaler); ok {
		return u.XXX_Unmarshal(buf)
	}
	if u, ok := pb.(Unmarshaler); ok {
		// NOTE: The history of proto have unfortunately been inconsistent
		// whether Unmarshaler should or should not implicitly clear itself.
		// Some implementations do, most do not.
		// Thus, calling this here may or may not do what people want.
		//
		// See https://github.com/golang/protobuf/issues/424
		return u.Unmarshal(buf)
	}
	return NewBuffer(buf).Unmarshal(pb)
}