Add mixed-script detection

Author: Manishearth

Cargo.toml

@@ -16,6 +16,7 @@ according to Unicode Technical Standard #39 rules.
 exclude = [ "target/*", "Cargo.lock" ]
 
 [dependencies]
+unicode-script = { git = "https://github.com/unicode-rs/unicode-script", default-features = false }
 std = { version = "1.0", package = "rustc-std-workspace-std", optional = true }
 core = { version = "1.0", package = "rustc-std-workspace-core", optional = true }
 compiler_builtins = { version = "0.1", optional = true }

src/lib.rs

@@ -58,6 +58,8 @@ extern crate test;
 use tables::identifier_status as is;
 pub use tables::UNICODE_VERSION;
 
+pub mod mixed_script;
+
 mod tables;
 
 #[cfg(test)]

src/mixed_script.rs

@@ -0,0 +1,121 @@
+//! [Mixed-script detection](https://www.unicode.org/reports/tr39/#Mixed_Script_Detection)
+
+use unicode_script::{Script, ScriptExtension};
+
+/// An Augmented script set, as defined by UTS 39
+///
+/// https://www.unicode.org/reports/tr39/#def-augmented-script-set
+pub struct AugmentedScriptSet {
+    /// The base ScriptExtension value
+    pub base: ScriptExtension,
+    /// Han With Bopomofo
+    pub hanb: bool,
+    /// Japanese
+    pub jpan: bool,
+    /// Korean
+    pub kore: bool,
+}
+
+impl From<ScriptExtension> for AugmentedScriptSet {
+    fn from(ext: ScriptExtension) -> Self {
+        let mut hanb = false;
+        let mut jpan = false;
+        let mut kore = false;
+
+        if ext.contains_script(Script::Han) {
+            hanb = true;
+            jpan = true;
+            kore = true;
+        } else {
+            if ext.contains_script(Script::Hiragana) || ext.contains_script(Script::Katakana) {
+                jpan = true;
+            }
+
+            if ext.contains_script(Script::Hangul) {
+                kore = true;
+            }
+
+            if ext.contains_script(Script::Bopomofo) {
+                hanb = true;
+            }
+        }
+        Self {
+            base: ext,
+            hanb, jpan, kore
+        }
+    }
+}
+
+impl From<char> for AugmentedScriptSet {
+    fn from(c: char) -> Self {
+        AugmentedScriptSet::for_char(c)
+    }
+}
+
+impl From<&'_ str> for AugmentedScriptSet {
+    fn from(s: &'_ str) -> Self {
+        AugmentedScriptSet::for_str(s)
+    }
+}
+
+impl Default for AugmentedScriptSet {
+    fn default() -> Self {
+        AugmentedScriptSet {
+            base: ScriptExtension::Single(Script::Common),
+            hanb: true,
+            jpan: true,
+            kore: true,
+        }
+    }
+}
+
+impl AugmentedScriptSet {
+    /// Intersect this set with another
+    pub fn intersect(mut self, other: Self) -> Self {
+        self.base = self.base.intersect(other.base);
+        self.hanb = self.hanb && other.hanb;
+        self.jpan = self.jpan && other.jpan;
+        self.kore = self.kore && other.kore;
+        self
+    }
+
+    /// Check if the set is empty
+    pub fn is_empty(&self) -> bool {
+        self.base.is_empty() && ! self.hanb && !self.jpan && !self.kore
+    }
+
+    /// Construct an AugmentedScriptSet for a given character
+    pub fn for_char(c: char) -> Self {
+        ScriptExtension::from(c).into()
+    }
+
+    /// Find the [resolved script set](https://www.unicode.org/reports/tr39/#def-resolved-script-set) of a given string
+    pub fn for_str(s: &str) -> Self {
+        let mut set = AugmentedScriptSet::default();
+        for ch in s.chars() {
+            set = set.intersect(ch.into())
+        }
+        set
+    }
+}
+
+/// Extension trait for [mixed-script detection](https://www.unicode.org/reports/tr39/#Mixed_Script_Detection)
+pub trait MixedScript {
+    /// Check if a string is [single-script](https://www.unicode.org/reports/tr39/#def-single-script)
+    ///
+    /// Note that a single-script string may still contain multiple Script properties!
+    fn is_single_script(self) -> bool;
+
+    /// Find the [resolved script set](https://www.unicode.org/reports/tr39/#def-resolved-script-set) of a given string
+    fn resolve_script_set(self) -> AugmentedScriptSet;
+}
+
+impl MixedScript for &'_ str {
+    fn is_single_script(self) -> bool {
+        !AugmentedScriptSet::for_str(self).is_empty()
+    }
+
+    fn resolve_script_set(self) -> AugmentedScriptSet {
+        self.into()
+    }
+}