level.go

package level // github.com/go-kit/kit/log/level


type LogLevels int

const (
  Debug LogLevels = iota
  Info
  Warn
  Err
)

// main.go....

func main() {
  var logger log.Logger
  logger = log.NewLogfmtLogger(log.NewSyncWriter(os.Stderr))
  
  // A (no leveled logging)
  logger.Log(Level.Debug, "foo", "bar")
  // level=debug foo=bar

  // B
  l = logger.WithFilter(level.Filter(level.Debug)) // WithFilter returns a log.Logger
  l.Log(level.Debug, "foo", "bar")
  // foo=bar
  
  // C
  l = logger.WithFilter(level.Filter(level.Info))
  l.Log(Level.Debug, "foo","bar")
  // <nothing>
  
  // D
  l = logger.With(Level.Info)
  l = l.WithFilter(level.Filter(level.Info))
  // pass l to a library/struct that doesn't use levels to fix all logs from that library to Info
  // Assuming that that library/struct eventually starts to use levels (you submitted a PR right?)
  // This still works as the locally applied levels could take precedence over the global as the global
  // still applies the filter.
}