/rust/registry/src/index.crates.io-6f17d22bba15001f/icu_provider-1.5.0/src/fallback.rs

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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.
    /// 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!("zh").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()
    }
}

Coverage Report

Created: 2025-07-11 06:39

Line	Count	Source (jump to first uncovered line)
1		// This file is part of ICU4X. For terms of use, please see the file
2		// called LICENSE at the top level of the ICU4X source tree
3		// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
4
5		//! Options to define fallback behaviour.
6		//!
7		//! These options are consumed by the `LocaleFallbacker` in the `icu_locid_transforms` crate
8		//! (or the `icu::locid_transforms` module), but are defined here because they are used by `DataKey`.
9
10		use icu_locid::extensions::unicode::Key;
11
12		/// Hint for which subtag to prioritize during fallback.
13		///
14		/// For example, `"en-US"` might fall back to either `"en"` or `"und-US"` depending
15		/// on this enum.
16		#[derive(Debug, PartialEq, Eq, Copy, Clone, PartialOrd, Ord)]
17		#[non_exhaustive]
18		pub enum LocaleFallbackPriority {
19		/// Prioritize the language. This is the default behavior.
20		///
21		/// For example, `"en-US"` should go to `"en"` and then `"und"`.
22		Language,
23		/// Prioritize the region.
24		///
25		/// For example, `"en-US"` should go to `"und-US"` and then `"und"`.
26		Region,
27		/// Collation-specific fallback rules. Similar to language priority.
28		///
29		/// For example, `"zh-Hant"` goes to `"zh"` before `"und"`.
30		Collation,
31		}
32
33		impl LocaleFallbackPriority {
34		/// Const-friendly version of [`Default::default`].
35	0	pub const fn const_default() -> Self {
36	0	Self::Language
37	0	}
38		}
39
40		impl Default for LocaleFallbackPriority {
41	0	fn default() -> Self {
42	0	Self::const_default()
43	0	}
44		}
45
46		/// What additional data is required to load when performing fallback.
47		#[derive(Debug, PartialEq, Eq, Copy, Clone, PartialOrd, Ord)]
48		#[non_exhaustive]
49		pub enum LocaleFallbackSupplement {
50		/// Collation supplement
51		Collation,
52		}
53
54		/// Configuration settings for a particular fallback operation.
55		#[derive(Debug, Clone, PartialEq, Eq, Copy)]
56		#[non_exhaustive]
57		pub struct LocaleFallbackConfig {
58		/// Strategy for choosing which subtags to drop during locale fallback.
59		///
60		/// # Examples
61		///
62		/// Retain the language and script subtags until the final step:
63		///
64		/// ```
65		/// use icu::locid::locale;
66		/// use icu::locid_transform::fallback::LocaleFallbackConfig;
67		/// use icu::locid_transform::fallback::LocaleFallbackPriority;
68		/// use icu::locid_transform::LocaleFallbacker;
69		///
70		/// // Set up the fallback iterator.
71		/// let fallbacker = LocaleFallbacker::new();
72		/// let mut config = LocaleFallbackConfig::default();
73		/// config.priority = LocaleFallbackPriority::Language;
74		/// let mut fallback_iterator = fallbacker
75		/// .for_config(config)
76		/// .fallback_for(locale!("ca-ES-valencia").into());
77		///
78		/// // Run the algorithm and check the results.
79		/// assert_eq!(fallback_iterator.get(), &locale!("ca-ES-valencia").into());
80		/// fallback_iterator.step();
81		/// assert_eq!(fallback_iterator.get(), &locale!("ca-ES").into());
82		/// fallback_iterator.step();
83		/// assert_eq!(fallback_iterator.get(), &locale!("ca-valencia").into());
84		/// fallback_iterator.step();
85		/// assert_eq!(fallback_iterator.get(), &locale!("ca").into());
86		/// fallback_iterator.step();
87		/// assert_eq!(fallback_iterator.get(), &locale!("und").into());
88		/// ```
89		///
90		/// Retain the region subtag until the final step:
91		///
92		/// ```
93		/// use icu::locid::locale;
94		/// use icu::locid_transform::fallback::LocaleFallbackConfig;
95		/// use icu::locid_transform::fallback::LocaleFallbackPriority;
96		/// use icu::locid_transform::LocaleFallbacker;
97		///
98		/// // Set up the fallback iterator.
99		/// let fallbacker = LocaleFallbacker::new();
100		/// let mut config = LocaleFallbackConfig::default();
101		/// config.priority = LocaleFallbackPriority::Region;
102		/// let mut fallback_iterator = fallbacker
103		/// .for_config(config)
104		/// .fallback_for(locale!("ca-ES-valencia").into());
105		///
106		/// // Run the algorithm and check the results.
107		/// assert_eq!(fallback_iterator.get(), &locale!("ca-ES-valencia").into());
108		/// fallback_iterator.step();
109		/// assert_eq!(fallback_iterator.get(), &locale!("ca-ES").into());
110		/// fallback_iterator.step();
111		/// assert_eq!(fallback_iterator.get(), &locale!("und-ES-valencia").into());
112		/// fallback_iterator.step();
113		/// assert_eq!(fallback_iterator.get(), &locale!("und-ES").into());
114		/// fallback_iterator.step();
115		/// assert_eq!(fallback_iterator.get(), &locale!("und").into());
116		/// ```
117		pub priority: LocaleFallbackPriority,
118		/// An extension keyword to retain during locale fallback.
119		///
120		/// # Examples
121		///
122		/// ```
123		/// use icu::locid::locale;
124		/// use icu::locid_transform::fallback::LocaleFallbackConfig;
125		/// use icu::locid_transform::LocaleFallbacker;
126		///
127		/// // Set up the fallback iterator.
128		/// let fallbacker = LocaleFallbacker::new();
129		/// let mut config = LocaleFallbackConfig::default();
130		/// config.extension_key = Some(icu::locid::extensions::unicode::key!("nu"));
131		/// let mut fallback_iterator = fallbacker
132		/// .for_config(config)
133		/// .fallback_for(locale!("ar-EG-u-nu-latn").into());
134		///
135		/// // Run the algorithm and check the results.
136		/// assert_eq!(fallback_iterator.get(), &locale!("ar-EG-u-nu-latn").into());
137		/// fallback_iterator.step();
138		/// assert_eq!(fallback_iterator.get(), &locale!("ar-EG").into());
139		/// fallback_iterator.step();
140		/// assert_eq!(fallback_iterator.get(), &locale!("ar-u-nu-latn").into());
141		/// fallback_iterator.step();
142		/// assert_eq!(fallback_iterator.get(), &locale!("ar").into());
143		/// fallback_iterator.step();
144		/// assert_eq!(fallback_iterator.get(), &locale!("und").into());
145		/// ```
146		pub extension_key: Option<Key>,
147		/// Fallback supplement data key to customize fallback rules.
148		///
149		/// For example, most data keys for collation add additional parent locales, such as
150		/// "yue" to "zh-Hant", and data used for the `"-u-co"` extension keyword fallback.
151		///
152		/// Currently the only supported fallback supplement is `LocaleFallbackSupplement::Collation`, but more may be
153		/// added in the future.
154		///
155		/// # Examples
156		///
157		/// ```
158		/// use icu::locid::locale;
159		/// use icu::locid_transform::fallback::LocaleFallbackConfig;
160		/// use icu::locid_transform::fallback::LocaleFallbackPriority;
161		/// use icu::locid_transform::fallback::LocaleFallbackSupplement;
162		/// use icu::locid_transform::LocaleFallbacker;
163		///
164		/// // Set up the fallback iterator.
165		/// let fallbacker = LocaleFallbacker::new();
166		/// let mut config = LocaleFallbackConfig::default();
167		/// config.priority = LocaleFallbackPriority::Collation;
168		/// config.fallback_supplement = Some(LocaleFallbackSupplement::Collation);
169		/// let mut fallback_iterator = fallbacker
170		/// .for_config(config)
171		/// .fallback_for(locale!("yue-HK").into());
172		///
173		/// // Run the algorithm and check the results.
174		/// assert_eq!(fallback_iterator.get(), &locale!("yue-HK").into());
175		/// fallback_iterator.step();
176		/// assert_eq!(fallback_iterator.get(), &locale!("yue").into());
177		/// fallback_iterator.step();
178		/// assert_eq!(fallback_iterator.get(), &locale!("zh-Hant").into());
179		/// fallback_iterator.step();
180		/// assert_eq!(fallback_iterator.get(), &locale!("zh").into());
181		/// fallback_iterator.step();
182		/// assert_eq!(fallback_iterator.get(), &locale!("und").into());
183		/// ```
184		pub fallback_supplement: Option<LocaleFallbackSupplement>,
185		}
186
187		impl LocaleFallbackConfig {
188		/// Const version of [`Default::default`].
189	0	pub const fn const_default() -> Self {
190	0	Self {
191	0	priority: LocaleFallbackPriority::const_default(),
192	0	extension_key: None,
193	0	fallback_supplement: None,
194	0	}
195	0	}
196		}
197
198		impl Default for LocaleFallbackConfig {
199	0	fn default() -> Self {
200	0	Self::const_default()
201	0	}
202		}