Based on discussion in #7849, it seems like it would be interesting to use jiff instead of chrono, at the very least in date: this would make our life easier when handling timezones.

Dirty branch here: https://github.com/drinkcat/coreutils/tree/jiff-dirty .

I'll keep modifying this comment as I find issues.

• Format specifiers that are not supported:
  • %q (quarters)
  • %N (nanoseconds, for chrono we manually replaced this with %f)
  • %X (localization issue, can be replaced manually with %H:%M:%S for now, I think localization is also TBD in coreutils)
  • %:::z (see Some input in date are panicking the binary #3780)
• In ls, we need to print dates using the same format over and over again. chrono provides an optimized API for that use case: we parse the format string once, then use that to print many times (see fc6b896). I didn't do any benchmarking yet, but I suspect this might be an issue.

@BurntSushi FYI