Format long specific non-location format in 2.0

[Nerixyz]

Hi, I was trying the new 2.0.0-beta to format some time zones. I want to format the time like this: 12:08:19 Mitteleuropäische Normalzeit. I'm probably missing something, but it seems like that's not possible, neither with the Combo<T, Zs> (note that Combo<T, Z> can't be constructed) nor with the CompositeFieldSet::TimeZone:

use icu_datetime::{
    fieldsets::{
        enums::{CompositeFieldSet, TimeFieldSet, ZoneStyle},
        T, Z,
    },
    DateTimeFormatter,
};
use icu_locale_core::locale;
use icu_timezone::IxdtfParser;

fn main() {
    let zdt = IxdtfParser::new()
        .try_from_str("2024-08-08T12:08:19+01:00[Europe/Berlin]")
        .unwrap();

    let formatter = DateTimeFormatter::try_new(
        locale!("de").into(),
        CompositeFieldSet::TimeZone(TimeFieldSet::T(T::long()), ZoneStyle::Z),
    )
    .unwrap();
    dbg!(formatter.format_any_calendar(&zdt).to_string()); // 12:08:19 MEZ

    let formatter =
        DateTimeFormatter::try_new(locale!("de").into(), T::long().zone_z()).unwrap();
    dbg!(formatter.format_any_calendar(&zdt).to_string()); // 12:08:19 MEZ

    let formatter = DateTimeFormatter::try_new(locale!("de").into(), Z::long()).unwrap();
    dbg!(formatter.format_any_calendar(&zdt).to_string()); // Mitteleuropäische Normalzeit
}

As you can see, it's only possible to format the short specific non-location style, not the long one, when combined with a time.

Aside: the CompositeFieldSetSerde (experimental) specifies FieldSetField::Zone{Generic,Specific}{Short,Long} but they aren't used.
Aside2: the tests for the lengths are all skipped because none of them specify a semantic skeleton.

[sffc]

Good question!

There's code that always sets the time zone length to Short when it is combined with other fields:

icu4x/components/datetime/src/raw/neo.rs

Line 592 in 8717dfc

// Always use the short length for time zones when mixed with another field (Time)

This was done to reduce data size; however, I don't see it mentioned in UTS 35. And, even if we do this by default, there should at least be a way to get the other behavior (long time zone name).

The fix would involve adding support for Combo<T, Z>.