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: unionFile.go
    path of file: ./repos/goplantuml/vendor/github.com/spf13/afero
    
    the code of the file until where you have to start completion: package afero

import (
	"io"
	"os"
	"path/filepath"
	"syscall"
)

// The UnionFile implements the afero.File interface and will be returned
// when reading a directory present at least in the overlay or opening a file
// for writing.
//
// The calls to
// Readdir() and Readdirnames() merge the file os
    
func (f *UnionFile) Readdir(c int) (ofi []os.FileInfo, err error) {
	var merge DirsMerger = f.Merger
	if merge == nil {
		merge = defaultUnionMergeDirsFn
	}

	if f.off == 0 {
		var lfi []os.FileInfo
		if f.Layer != nil {
			lfi, err = f.Layer.Readdir(-1)
			if err != nil {
				return nil, err
			}
		}

		var bfi []os.FileInfo
		if f.Base != nil {
			bfi, err = f.Base.Readdir(-1)
			if err != nil {
				return nil, err
			}

		}
		merged, err := merge(lfi, bfi)
		if err != nil {
			return nil, err
		}
		f.files = append(f.files, merged...)
	}
	files := f.files[f.off:]

	if c <= 0 {
		return files, nil
	}

	if len(files) == 0 {
		return nil, io.EOF
	}

	if c > len(files) {
		c = len(files)
	}

	defer func() { f.off += c }()
	return files[:c], nil
}