go-logr and zerolog formatting for GCP stdout/stderr scraping

setup.go

func initialiseLogging() logr.Logger {
	// Setup structured logging to match Cloud Operations expectations, as much as possible
	zerolog.TimestampFieldName = "time"
	zerolog.TimeFieldFormat = time.RFC3339
	zerolog.LevelFieldName = "severity"
	zerolog.LevelTraceValue = "DEFAULT"
	zerolog.LevelDebugValue = "DEBUG"
	zerolog.LevelInfoValue = "INFO"
	zerolog.LevelWarnValue = "WARNING"
	zerolog.LevelErrorValue = "ERROR"
	zerolog.LevelFatalValue = "CRITICAL"
	zerolog.LevelPanicValue = "ALERT"
	zerolog.MessageFieldName = "message"
	zerolog.ErrorStackFieldName = "stack_trace" //nolint:reassign // This is not a sentinel error, just the name of a field
	// There isn't a good way to change caller info into an embedded struct
	// expected by Cloud Operations, so don't try.
	// See https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry#LogEntrySourceLocation
	// and https://github.com/rs/zerolog/issues/472
	// zerolog.CallerFieldName = "logging.googleapis.com/sourceLocation"
	// zerolog.CallerMarshalFunc = func(_ uintptr, file string, line int) string {
		// ...
	// }
	if os.Getenv("DEBUG") == "" {
		zerolog.SetGlobalLevel(zerolog.InfoLevel)
	} else {
		zerolog.SetGlobalLevel(zerolog.TraceLevel)
	}
	zl := zerolog.New(os.Stdout).With().Caller().Timestamp().Logger()
	return zerologr.New(&zl)
}