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// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
//! Options to define fallback behaviour.
//!
//! These options are consumed by the `LocaleFallbacker` in the `icu_locid_transforms` crate
//! (or the `icu::locid_transforms` module), but are defined here because they are used by `DataKey`.
use icu_locid::extensions::unicode::Key;
/// Hint for which subtag to prioritize during fallback.
///
/// For example, `"en-US"` might fall back to either `"en"` or `"und-US"` depending
/// on this enum.
#[derive(Debug, PartialEq, Eq, Copy, Clone, PartialOrd, Ord)]
#[non_exhaustive]
pub enum LocaleFallbackPriority {
/// Prioritize the language. This is the default behavior.
///
/// For example, `"en-US"` should go to `"en"` and then `"und"`.
Language,
/// Prioritize the region.
///
/// For example, `"en-US"` should go to `"und-US"` and then `"und"`.
Region,
/// Collation-specific fallback rules. Similar to language priority.
///
/// For example, `"zh-Hant"` goes to `"zh"` before `"und"`.
Collation,
}
impl LocaleFallbackPriority {
/// Const-friendly version of [`Default::default`].
pub const fn const_default() -> Self {
Self::Language
}
}
impl Default for LocaleFallbackPriority {
fn default() -> Self {
Self::const_default()
}
}
/// What additional data is required to load when performing fallback.
#[derive(Debug, PartialEq, Eq, Copy, Clone, PartialOrd, Ord)]
#[non_exhaustive]
pub enum LocaleFallbackSupplement {
/// Collation supplement
Collation,
}
/// Configuration settings for a particular fallback operation.
#[derive(Debug, Clone, PartialEq, Eq, Copy)]
#[non_exhaustive]
pub struct LocaleFallbackConfig {
/// Strategy for choosing which subtags to drop during locale fallback.
///
/// # Examples
///
/// Retain the language and script subtags until the final step:
///
/// ```
/// use icu_locid::locale;
/// use icu_locid_transform::fallback::LocaleFallbackConfig;
/// use icu_locid_transform::fallback::LocaleFallbackPriority;
/// use icu_locid_transform::LocaleFallbacker;
///
/// // Set up the fallback iterator.
/// let fallbacker = LocaleFallbacker::new();
/// let mut config = LocaleFallbackConfig::default();
/// config.priority = LocaleFallbackPriority::Language;
/// let mut fallback_iterator = fallbacker
/// .for_config(config)
/// .fallback_for(locale!("ca-ES-valencia").into());
///
/// // Run the algorithm and check the results.
/// assert_eq!(fallback_iterator.get(), &locale!("ca-ES-valencia").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("ca-ES").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("ca-valencia").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("ca").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("und").into());
/// ```
///
/// Retain the region subtag until the final step:
///
/// ```
/// use icu_locid::locale;
/// use icu_locid_transform::fallback::LocaleFallbackConfig;
/// use icu_locid_transform::fallback::LocaleFallbackPriority;
/// use icu_locid_transform::LocaleFallbacker;
///
/// // Set up the fallback iterator.
/// let fallbacker = LocaleFallbacker::new();
/// let mut config = LocaleFallbackConfig::default();
/// config.priority = LocaleFallbackPriority::Region;
/// let mut fallback_iterator = fallbacker
/// .for_config(config)
/// .fallback_for(locale!("ca-ES-valencia").into());
///
/// // Run the algorithm and check the results.
/// assert_eq!(fallback_iterator.get(), &locale!("ca-ES-valencia").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("ca-ES").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("und-ES-valencia").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("und-ES").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("und").into());
/// ```
pub priority: LocaleFallbackPriority,
/// An extension keyword to retain during locale fallback.
///
/// # Examples
///
/// ```
/// use icu_locid::locale;
/// use icu_locid_transform::fallback::LocaleFallbackConfig;
/// use icu_locid_transform::LocaleFallbacker;
///
/// // Set up the fallback iterator.
/// let fallbacker = LocaleFallbacker::new();
/// let mut config = LocaleFallbackConfig::default();
/// config.extension_key = Some(icu_locid::extensions::unicode::key!("nu"));
/// let mut fallback_iterator = fallbacker
/// .for_config(config)
/// .fallback_for(locale!("ar-EG-u-nu-latn").into());
///
/// // Run the algorithm and check the results.
/// assert_eq!(fallback_iterator.get(), &locale!("ar-EG-u-nu-latn").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("ar-EG").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("ar-u-nu-latn").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("ar").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("und").into());
/// ```
pub extension_key: Option<Key>,
/// Fallback supplement data key to customize fallback rules.
///
/// For example, most data keys for collation add additional parent locales, such as
/// "yue" to "zh-Hant", and data used for the `"-u-co"` extension keyword fallback.
///
/// Currently the only supported fallback supplement is `LocaleFallbackSupplement::Collation`, but more may be
/// added in the future.
///
/// # Examples
///
/// ```
/// use icu_locid::locale;
/// use icu_locid_transform::fallback::LocaleFallbackConfig;
/// use icu_locid_transform::fallback::LocaleFallbackPriority;
/// use icu_locid_transform::fallback::LocaleFallbackSupplement;
/// use icu_locid_transform::LocaleFallbacker;
///
/// // Set up the fallback iterator.
/// let fallbacker = LocaleFallbacker::new();
/// let mut config = LocaleFallbackConfig::default();
/// config.priority = LocaleFallbackPriority::Collation;
/// config.fallback_supplement = Some(LocaleFallbackSupplement::Collation);
/// let mut fallback_iterator = fallbacker
/// .for_config(config)
/// .fallback_for(locale!("yue-HK").into());
///
/// // Run the algorithm and check the results.
/// // TODO(#1964): add "zh" as a target.
/// assert_eq!(fallback_iterator.get(), &locale!("yue-HK").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("yue").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("zh-Hant").into());
/// fallback_iterator.step();
/// assert_eq!(fallback_iterator.get(), &locale!("und").into());
/// ```
pub fallback_supplement: Option<LocaleFallbackSupplement>,
}
impl LocaleFallbackConfig {
/// Const version of [`Default::default`].
pub const fn const_default() -> Self {
Self {
priority: LocaleFallbackPriority::const_default(),
extension_key: None,
fallback_supplement: None,
}
}
}
impl Default for LocaleFallbackConfig {
fn default() -> Self {
Self::const_default()
}
}
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