Leveled fields: Fields present only at certain log levels

An issue that users sometimes have is this:

They have a log statement like the following,

logger.Info("processing request", zap.String("fromUser", fromUser))

They would like to include additional information in that log statement, but only if the debug level is enabled.

Currently, the options are:

1. Copy paste the log statement

if debugLevel {
  logger.Info("processing request", zap.String("fromUser", fromUser), zap.Object("request", request))
} else {
  logger.Info("processing request", zap.String("fromUser", fromUser))
}

2. Add another log statement

logger.Info("processing request", zap.String("fromUser", fromUser))
logger.Debug("processing request", zap.Object("request", request))

3. custom helpers like the following:

func levelField(log *zap.Logger, lvl zap.Level, field zap.Field) zap.Field {
  if !log.Core().Enabled(lvl) { return zap.Skip() }
  return field
}

logger.Info("processing request",
  zap.String("fromUser", fromUser),
  levelField(logger, zap.DebugLevel, zap.Object("request", request)))

I think it might be valuable for Zap to natively provide some concept of "leveled fields"—fields present only at certain log levels—based on something like the levelField helper above.

I don't have an exact design in mind, but Zap-native support for something like this would likely be able to drop that extra log argument.