Attribute Macro data_struct

#[data_struct]

The #[data_struct] attribute should be applied to all types intended for use in a DataStruct.

It does the following things:

• Apply #[derive(Yokeable, ZeroFrom)]. The ZeroFrom derive can be customized with #[zerofrom(clone)] on non-ZeroFrom fields.

In addition, the attribute can be used to implement DataMarker and/or KeyedDataMarker by adding symbols with optional key strings:

use icu::locid::extensions::unicode::key;
use icu::locid_transform::fallback::*;
use icu_provider::yoke;
use icu_provider::zerofrom;
use icu_provider::KeyedDataMarker;
use std::borrow::Cow;

#[icu_provider::data_struct(
    FooV1Marker,
    BarV1Marker = "demo/bar@1",
    marker(
        BazV1Marker,
        "demo/baz@1",
        fallback_by = "region",
        extension_key = "ca"
    )
)]
pub struct FooV1<'data> {
    message: Cow<'data, str>,
};

// Note: FooV1Marker implements `DataMarker` but not `KeyedDataMarker`.
// The other two implement `KeyedDataMarker`.

assert_eq!(&*BarV1Marker::KEY.path(), "demo/bar@1");
assert_eq!(
    BarV1Marker::KEY.metadata().fallback_priority,
    LocaleFallbackPriority::Language
);
assert_eq!(BarV1Marker::KEY.metadata().extension_key, None);

assert_eq!(&*BazV1Marker::KEY.path(), "demo/baz@1");
assert_eq!(
    BazV1Marker::KEY.metadata().fallback_priority,
    LocaleFallbackPriority::Region
);
assert_eq!(BazV1Marker::KEY.metadata().extension_key, Some(key!("ca")));

If the #[databake(path = ...)] attribute is present on the data struct, this will also implement it on the markers.