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: legacy_file.go
    path of file: ./repos/scan4all/vendor/google.golang.org/protobuf/internal/impl
    
    the code of the file until where you have to start completion: // Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package impl

import (
	"bytes"
	"compress/gzip"
	"io/ioutil"
	"sync"

	"google.golang.org/protobuf/internal/filedesc"
	"google.golang.org/protobuf/reflect/protoreflect"
	"google.golang.org/protobuf/reflect/protoregistry"
)

// Every enum and message type generated by protoc-gen-go since commit 2fc053c5
// on February 25th, 2016 has had a method to get the raw descriptor.
// Types that were not generated by protoc-gen-go or were generated prior
    
func legacyLoadFileDesc(b []byte) protoreflect.FileDescriptor {
	// Fast-path: check whether we already have a cached file descriptor.
	if fd, ok := legacyFileDescCache.Load(&b[0]); ok {
		return fd.(protoreflect.FileDescriptor)
	}

	// Slow-path: decompress and unmarshal the file descriptor proto.
	zr, err := gzip.NewReader(bytes.NewReader(b))
	if err != nil {
		panic(err)
	}
	b2, err := ioutil.ReadAll(zr)
	if err != nil {
		panic(err)
	}

	fd := filedesc.Builder{
		RawDescriptor: b2,
		FileRegistry:  resolverOnly{protoregistry.GlobalFiles}, // do not register back to global registry
	}.Build().File
	if fd, ok := legacyFileDescCache.LoadOrStore(&b[0], fd); ok {
		return fd.(protoreflect.FileDescriptor)
	}
	return fd
}