Dump configuration struct with defaults

dump.go

func DumpConfig(s interface{}) {
	var dump func(interface{}, int)
	dump = func(s interface{}, level int) {
		e := reflect.ValueOf(s)
		t := e.Type()
		for i := 0; i < e.NumField(); i++ {
			f := e.Field(i)
			ft := t.Field(i)
			if !ft.Anonymous {
				fmt.Printf("%s%s:", strings.Repeat("  ", level), tagName(ft))
			}
			if f.Kind() == reflect.Struct {
				fmt.Println()
				if ft.Anonymous {
					dump(f.Interface(), level)
				} else  {
					dump(f.Interface(), level+1)
				}
			} else {
				fmt.Printf(" %s", ft.Type)
				if !f.IsZero() {
					fmt.Printf(" (default: %#v)", f.Interface())
				}
				fmt.Println()
			}
		}
	}
	dump(s, 0)
}

func tagName(f reflect.StructField) string {
	return strings.SplitN(tagValue(f), ",", 2)[0]
}

func tagValue(f reflect.StructField) string {
	for _, key := range []string{"json", "mapstructure"} {
		if v, ok := f.Tag.Lookup(key); ok {
			return v
		}
	}
	return f.Name
}