Let ZoneDateTime parse date time strings with reduced precision to be more ISO8601 compliant.

[Para7etamol]

Hi there,

I feel this is related to #470, but has another focus.

ISO8601 generally allows to drop the least-significant components of the time specification. Consequently DateTime can parse

julia> dt=DateTime("2026-01-20T09:00",dateformat"yyyy-mm-dd\THH:MM:SS")
2026-01-20T09:00:00

where the seconds are left out although they are specified. DateTime adds zeros here.

I would love ZonedDateTime to do the same, but

julia> zdt=ZonedDateTime("2026-01-20T09:00+01:00",dateformat"yyyy-mm-dd\THH:MM:SSzzz")
ERROR: ArgumentError: Unable to parse string "2026-01-20T09:00+01:00" using format dateformat"yyyy-mm-dd\THH:MM:SSzzz". Unable to parse date time. Expected directive Delim(:) at char 17
Stacktrace: ...

For millis it's nearly the same story, because DateTime omits them in the output if zero instead of adding zeros:

julia> dt=DateTime("2026-01-20T09:00",dateformat"yyyy-mm-dd\THH:MM:SS.sss")
2026-01-20T09:00:00

So aside from better ISO 8601 compliance, maybe it could fix #470, if ZonedDateTime would allow dropping the least-significant parts.

Sincerly yours

Para7etamol

[omus]

Thanks for the issue. TimeZones.jl uses the same date formatting provided by Dates.jl so it can be a bit challenging to update this behavior. I do agree this would be a nice feature to have though.