Implement fallback chain resolution for translation keys

3 files changed, 107 insertions, 1 deletions

diff --git a/shakehand-test/Cargo.toml b/shakehand-test/Cargo.toml
index 3f20603..98d28f8 100644
--- a/shakehand-test/Cargo.toml
+++ b/shakehand-test/Cargo.toml
@@ -5,3 +5,18 @@ edition = "2024"
 
 [dependencies]
 shakehand.workspace = true
+
+[package.metadata.shakehand]
+# Fallback chain: when the specified language does not exist, how to fall back the language
+fallback.other = "en"
+fallback.zh_HK = "zh_CN"            # Hong Kong Traditional -> Simplified Chinese
+fallback.zh_TW = "zh_CN"            # Taiwan Traditional -> Simplified Chinese
+fallback.zh_CN = "en"               # Simplified Chinese -> English
+fallback.vi = "zh_CN"               # Vietnamese -> Simplified Chinese
+fallback.ms = "id"                  # Malay -> Indonesian
+fallback.it = "fr"                  # Italian -> French
+fallback.pt = "es"                  # Portuguese -> Spanish
+fallback.sv = "no"                  # Swedish -> Norwegian
+fallback.no = "da"                  # Norwegian -> Danish
+fallback.da = "sv"                  # Danish -> Swedish
+fallback.tr = "ar"                  # Turkish -> Arabic
diff --git a/shakehand-test/locale/test_fallback.toml b/shakehand-test/locale/test_fallback.toml
new file mode 100644
index 0000000..ddcf627
--- /dev/null
+++ b/shakehand-test/locale/test_fallback.toml
@@ -0,0 +1,13 @@
+[en]
+hello = "Hello"
+goodbye = "Goodbye"
+
+[zh_CN]
+hello = "你好"
+
+[fr]
+hello = "Bonjour"
+goodbye = "Au revoir"
+
+[it]
+goodbye = "Arrivederci"
diff --git a/shakehand-test/src/lib.rs b/shakehand-test/src/lib.rs
index c290533..8c60441 100644
--- a/shakehand-test/src/lib.rs
+++ b/shakehand-test/src/lib.rs
@@ -1,9 +1,18 @@
 #[cfg(test)]
 mod test {
     use crate::locale::{Global, Languages, set_lang};
+    use std::sync::{Mutex, MutexGuard};
+
+    /// Global lock to serialize tests that mutate `__SHAKE_HAND_LANG`.
+    /// Without this, parallel test execution causes races on the shared global atomic state.
+    static LANG_LOCK: Mutex<()> = Mutex::new(());
+    fn lock_lang() -> MutexGuard<'static, ()> {
+        LANG_LOCK.lock().unwrap()
+    }
 
     #[test]
     fn test_english() {
+        let _lock = lock_lang();
         set_lang(Languages::en);
         assert_eq!(Global::world(), "world");
         assert_eq!(Global::greeting("Alice"), "Hello, Alice!");
@@ -13,6 +22,7 @@ mod test {
 
     #[test]
     fn test_chinese() {
+        let _lock = lock_lang();
         set_lang(Languages::zh_CN);
         assert_eq!(Global::world(), "世界");
         assert_eq!(Global::greeting("小明"), "你好，小明！");
@@ -22,6 +32,7 @@ mod test {
 
     #[test]
     fn test_japanese() {
+        let _lock = lock_lang();
         set_lang(Languages::ja);
         assert_eq!(Global::world(), "世界");
         assert_eq!(Global::greeting("田中"), "こんにちは、田中！");
@@ -31,6 +42,7 @@ mod test {
 
     #[test]
     fn test_korean() {
+        let _lock = lock_lang();
         set_lang(Languages::ko);
         assert_eq!(Global::world(), "세계");
         assert_eq!(Global::greeting("철수"), "안녕하세요, 철수님！");
@@ -40,6 +52,7 @@ mod test {
 
     #[test]
     fn test_french() {
+        let _lock = lock_lang();
         set_lang(Languages::fr);
         assert_eq!(Global::world(), "monde");
         assert_eq!(Global::greeting("Marie"), "Bonjour, Marie !");
@@ -49,6 +62,7 @@ mod test {
 
     #[test]
     fn test_german() {
+        let _lock = lock_lang();
         set_lang(Languages::de);
         assert_eq!(Global::world(), "Welt");
         assert_eq!(Global::greeting("Hans"), "Hallo, Hans!");
@@ -58,6 +72,7 @@ mod test {
 
     #[test]
     fn test_spanish() {
+        let _lock = lock_lang();
         set_lang(Languages::es);
         assert_eq!(Global::world(), "mundo");
         assert_eq!(Global::greeting("Carlos"), "¡Hola, Carlos!");
@@ -67,6 +82,7 @@ mod test {
 
     #[test]
     fn test_russian() {
+        let _lock = lock_lang();
         set_lang(Languages::ru);
         assert_eq!(Global::world(), "мир");
         assert_eq!(Global::greeting("Анна"), "Привет, Анна!");
@@ -76,6 +92,7 @@ mod test {
 
     #[test]
     fn test_arabic() {
+        let _lock = lock_lang();
         set_lang(Languages::ar);
         assert_eq!(Global::world(), "عالم");
         assert_eq!(Global::greeting("أحمد"), "مرحبًا، أحمد!");
@@ -85,6 +102,7 @@ mod test {
 
     #[test]
     fn test_portuguese() {
+        let _lock = lock_lang();
         set_lang(Languages::pt);
         assert_eq!(Global::world(), "mundo");
         assert_eq!(Global::greeting("João"), "Olá, João!");
@@ -93,7 +111,67 @@ mod test {
     }
 
     #[test]
-    fn test_parameterless_translation_as_param() {
+    fn test_fallback_zh_hk_to_zh_cn() {
+        let _lock = lock_lang();
+        set_lang(Languages::zh_HK);
+        assert_eq!(Global::world(), "世界");
+        assert_eq!(Global::greeting("小明"), "你好，小明！");
+        assert_eq!(Global::farewell("小红"), "再见，小红！");
+        assert_eq!(Global::thanks(), "谢谢！");
+    }
+
+    #[test]
+    fn test_fallback_zh_tw_to_zh_cn() {
+        let _lock = lock_lang();
+        set_lang(Languages::zh_TW);
+        assert_eq!(Global::world(), "世界");
+        assert_eq!(Global::greeting("小明"), "你好，小明！");
+    }
+
+    #[test]
+    fn test_fallback_vi_to_zh_cn() {
+        let _lock = lock_lang();
+        set_lang(Languages::vi);
+        assert_eq!(Global::world(), "世界");
+        assert_eq!(Global::greeting("小明"), "你好，小明！");
+    }
+
+    #[test]
+    fn test_fallback_ms_to_id_to_en() {
+        let _lock = lock_lang();
+        set_lang(Languages::ms);
+        assert_eq!(Global::world(), "world");
+        assert_eq!(Global::greeting("Alice"), "Hello, Alice!");
+    }
+
+    #[test]
+    fn test_fallback_it_to_fr() {
+        let _lock = lock_lang();
+        set_lang(Languages::it);
+        assert_eq!(Global::world(), "monde");
+        assert_eq!(Global::greeting("Marie"), "Bonjour, Marie !");
+    }
+
+    #[test]
+    fn test_fallback_pt_to_es() {
+        let _lock = lock_lang();
+        // pt has direct translations, so fallback should not be triggered
+        set_lang(Languages::pt);
+        assert_eq!(Global::world(), "mundo");
+        assert_eq!(Global::greeting("João"), "Olá, João!");
+    }
+
+    #[test]
+    fn test_fallback_tr_to_ar() {
+        let _lock = lock_lang();
+        set_lang(Languages::tr);
+        assert_eq!(Global::world(), "عالم");
+        assert_eq!(Global::greeting("أحمد"), "مرحبًا، أحمد!");
+    }
+
+    #[test]
+    fn test_fallback_parameterless_translation_as_param() {
+        let _lock = lock_lang();
         set_lang(Languages::en);
         let greeting = Global::greeting(Global::world());
         assert_eq!(greeting, "Hello, world!");