ISO8601 Ordinal Date support?

[soulstompp]

I am working on a set of parsers based on winnow https://crates.io/crates/winnow_datetime which support parsing common date time formats (currently ISO8601 and RFC3999). So far, adding conversions from the existing AST to jiff has been wonderfully straight forward. However, I don't see a way to create a civil::Date object from the ordinal dates (i.e. 2024-122) which is supported by ISO8601?

Is support for creating a date for ordinal dates along the lines of civil::ISOWeekDate possible? I am not sure if the internal parser supports this format, but I would like to avoid reparsing the date value if at all possible.

[BurntSushi]

If you're looking to parse 2024-122, then that can be done with Jiff's strptime APIs:

use jiff::civil;

fn main() -> anyhow::Result<()> {
    let date = civil::Date::strptime("%Y-%j", "2024-122")?;
    assert_eq!(date, civil::date(2024, 5, 1));

    Ok(())
}

But it sounds like you are owning the parsing. In that case, you'll want to use Date::with to do those sorts of manipulations. It returns a builder which lets you set a number of fields. The with APIs are available on all datetime types, including on Zoned. Here's how to do it:

use jiff::civil;

fn main() -> anyhow::Result<()> {
    let date =
        civil::Date::new(2024, 1, 1)?.with().day_of_year(122).build()?;
    assert_eq!(date, civil::date(2024, 5, 1));

    Ok(())
}

ISOWeekDate gets its own type because it is actually a different calendar system.

Jiff provides with() builders for this sort of thing instead of methods on Date proper because it avoids the problem of accidentally creating an intermediate invalid value. There are examples demonstrating their utility.

[soulstompp]

I hadn't considered the ISOWeekdate actually being a different calendar system, makes sense why it would be its own thing.

I forgot to check the with() builders, I was using those at the beginning and things went smoothly enough without it I sort of forgot it existed. I will get the ordinal dates stuff patched up here shortly. Thanks!

[BurntSushi]

I am working on a set of parsers based on winnow https://crates.io/crates/winnow_datetime which support parsing common date time formats (currently ISO8601 and RFC3999)

Taking a quick look here, one thing I'd suggest adding is time zone support. Specifically, RFC 9557.

Note also that Jiff supports the Temporal ISO 8601 grammar. It is a marriage of ISO 8601, RFC 3339 and RFC 9557.

[soulstompp]

These are both really great suggestions, I hadn't even heard of these until starting to read through the jiff documentation. Getting the time zone portion going would definitely be helpful, and hopefully the Temporal ISO 8601 can mostly share code with the parsers from the other three specs.

Just as a note, writing these parsers has been a fairly daunting task, and I know that parsing is a tiny/simple step compared to the complexities of the validation and arithmetic needed to make a full date time library. I am a big fan of what you have done here, and definitely have a new-found respect for the brain power needed behind it. Thanks for this library, it's incredibly well done.

[BurntSushi]

Thank you! :-)

Temporal really helped a ton here. They really paved the way.

[soulstompp]

Taking a quick look here, one thing I'd suggest adding is time zone support. Specifically, RFC 9557.

I just wanted to follow up and mention that there is now a crate that supports RFC 9557 available as [winnow-rfc9557][https://crates.io/crates/winnow_rfc9557]. The [winnow-datetime][https://crates.io/crates/winnow_datetime] objects export the named time zone when converting to a jiff::Zoned object.

Thanks for pointing this RFC to me, it was a great addition to the winnow-datetime family.

[BurntSushi]

Nice!