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: completion.go
    path of file: ./repos/sealer/vendor/github.com/containers/common/pkg/completion
    
    the code of the file until where you have to start completion: package completion

import (
	"bufio"
	"os"
	"strings"
	"unicode"

	"github.com/containers/common/pkg/capabilities"
	"github.com/spf13/cobra"
)

// FlagCompletions - hold flag completion functions to be applied later with CompleteCommandFlags()
type FlagCompletions map[string]func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellC
    
func autocompleteSubIDName(filename string) ([]string, cobra.ShellCompDirective) {
	file, err := os.Open(filename)
	if err != nil {
		return nil, cobra.ShellCompDirectiveError
	}
	defer file.Close()

	var names []string
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		name := strings.SplitN(scanner.Text(), ":", 2)[0]
		names = append(names, name)
	}
	if err = scanner.Err(); err != nil {
		return nil, cobra.ShellCompDirectiveError
	}

	return names, cobra.ShellCompDirectiveNoFileComp
}