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: completions.go
    path of file: ./repos/apns2/vendor/gopkg.in/alecthomas/kingpin.v2
    
    the code of the file until where you have to start completion: package kingpin

// HintAction is a function type who is expected to return a slice of possible
// command line arguments.
type HintAction fun
    
func (a *completionsMixin) resolveCompletions() []string {
	var hints []string

	options := a.builtinHintActions
	if len(a.hintActions) > 0 {
		// User specified their own hintActions. Use those instead.
		options = a.hintActions
	}

	for _, hintAction := range options {
		hints = append(hints, hintAction()...)
	}
	return hints
}