How to show 9 digits of precision when formatting subseconds for a custom timer implementation?

[twitu]

I've tried different variations of UtcTime and it does show 9 digits of precision for subseconds but the last 3 digits (the nanoseconds) are 0. I suspect the formatter supports 9 digits but the underlying timer being used doesn't have that level of precision.

let timer = UtcTime::new(format_description!(
    "[year]-[month]-[day]T[hour repr:24]:[minute]:[second].[subsecond digits:9]Z"));
let timer = UtcTime::rfc_3339();
let timer = UtcTime::new(Iso8601::DEFAULT);

        fmt::Layer::default()
            .with_timer(timer)
            .with_writer(std::io::stdout());

2023-08-12T13:57:39.733650000  WARN core: Pew pew component="alien"
2023-08-12T13:58:54.905663000Z  WARN core: Pew pew component="alien"

The default formatter only shows 6 digits.

2023-08-12T13:16:05.188268Z  WARN core: Pew pew component="alien"

[twitu]

According to the SystemTime page ¹ the clock resolution is platform dependent and on Mac M2 it does not have nanosecond resolution. Since most clocks in tracing subscriber internally use SystemTime calls this is not possible.

Footnotes

1. https://doc.rust-lang.org/std/time/struct.SystemTime.html#platform-specific-behavior ↩