Fix crash of trans() function called on absent translation key (#793)

Add method get_translation(lang, key) into Config struct that retrieves
translated term from parsed configuration or error when either
desired language or key is missing.

Use the new method in Trans struct implementing global Tera function
trans().

Add unit test to cover both happy and error path for translation
retrieval in both config and templates crate.

components/config/src/config.rs

@@ -8,6 +8,7 @@ use toml;
 use toml::Value as Toml;
 
 use errors::Result;
+use errors::Error;
 use highlighting::THEME_SET;
 use theme::Theme;
 use utils::fs::read_file_with_error;
@@ -83,6 +84,8 @@ impl Default for Taxonomy {
     }
 }
 
+type TranslateTerm  = HashMap<String, String>;
+
 #[derive(Clone, Debug, Serialize, Deserialize)]
 #[serde(default)]
 pub struct Config {
@@ -100,8 +103,12 @@ pub struct Config {
     pub default_language: String,
     /// The list of supported languages outside of the default one
     pub languages: Vec<Language>,
+
     /// Languages list and translated strings
-    pub translations: HashMap<String, Toml>,
+    ///
+    /// The `String` key of `HashMap` is a language name, the value should be toml crate `Table`
+    /// with String key representing term and value another `String` representing its translation.
+    pub translations: HashMap<String, TranslateTerm>,
 
     /// Whether to highlight all code blocks found in markdown files. Defaults to false
     pub highlight_code: bool,
@@ -299,6 +306,16 @@ impl Config {
         // and this operation can be expensive.
         self.highlight_code = false;
     }
+
+    pub fn get_translation<S: AsRef<str>>(&self, lang: S, key: S) -> Result<String> {
+        let terms = self.translations.get(lang.as_ref()).ok_or_else(|| {
+            Error::msg(format!("Translation for language '{}' is missing", lang.as_ref()))
+        })?;
+
+        terms.get(key.as_ref()).ok_or_else(|| {
+            Error::msg(format!("Translation key '{}' for language '{}' is missing", key.as_ref(), lang.as_ref()))
+        }).map(|term| term.to_string())
+    }
 }
 
 impl Default for Config {
@@ -447,9 +464,7 @@ a_value = 10
         assert_eq!(extra["a_value"].as_integer().unwrap(), 10);
     }
 
-    #[test]
-    fn can_use_language_configuration() {
-        let config = r#"
+    const CONFIG_TRANSLATION: &str = r#"
 base_url = "https://remplace-par-ton-url.fr"
 default_language = "fr"
 
@@ -459,14 +474,38 @@ title = "Un titre"
 
 [translations.en]
 title = "A title"
-
         "#;
 
-        let config = Config::parse(config);
+    #[test]
+    fn can_use_language_configuration() {
+        let config = Config::parse(CONFIG_TRANSLATION);
         assert!(config.is_ok());
         let translations = config.unwrap().translations;
-        assert_eq!(translations["fr"]["title"].as_str().unwrap(), "Un titre");
-        assert_eq!(translations["en"]["title"].as_str().unwrap(), "A title");
+        assert_eq!(translations["fr"]["title"].as_str(), "Un titre");
+        assert_eq!(translations["en"]["title"].as_str(), "A title");
+    }
+
+    #[test]
+    fn can_use_present_translation() {
+        let config = Config::parse(CONFIG_TRANSLATION).unwrap();
+        assert_eq!(config.get_translation("fr", "title").unwrap(), "Un titre");
+        assert_eq!(config.get_translation("en", "title").unwrap(), "A title");
+    }
+
+    #[test]
+    fn error_on_absent_translation_lang() {
+        let config = Config::parse(CONFIG_TRANSLATION).unwrap();
+        let error = config.get_translation("absent", "key").unwrap_err();
+
+        assert_eq!("Translation for language 'absent' is missing", format!("{}", error));
+    }
+
+    #[test]
+    fn error_on_absent_translation_key() {
+        let config = Config::parse(CONFIG_TRANSLATION).unwrap();
+        let error = config.get_translation("en", "absent").unwrap_err();
+
+        assert_eq!("Translation key 'absent' for language 'en' is missing", format!("{}", error));
     }
 
     #[test]

components/templates/src/global_fns/mod.rs

@@ -33,8 +33,12 @@ impl TeraFn for Trans {
         let key = required_arg!(String, args.get("key"), "`trans` requires a `key` argument.");
         let lang = optional_arg!(String, args.get("lang"), "`trans`: `lang` must be a string.")
             .unwrap_or_else(|| self.config.default_language.clone());
-        let translations = &self.config.translations[lang.as_str()];
-        Ok(to_value(&translations[key.as_str()]).unwrap())
+
+        let term = self.config.get_translation(lang, key).map_err(|e| {
+            Error::chain("Failed to retreive term translation", e)
+        })?;
+
+        Ok(to_value(term).unwrap())
     }
 }
 
@@ -505,9 +509,8 @@ mod tests {
         assert!(static_fn.call(&args).is_err());
     }
 
-    #[test]
-    fn can_translate_a_string() {
-        let trans_config = r#"
+
+    const TRANS_CONFIG: &str = r#"
 base_url = "https://remplace-par-ton-url.fr"
 default_language = "fr"
 
@@ -517,10 +520,11 @@ title = "Un titre"
 
 [translations.en]
 title = "A title"
-
         "#;
 
-        let config = Config::parse(trans_config).unwrap();
+    #[test]
+    fn can_translate_a_string() {
+        let config = Config::parse(TRANS_CONFIG).unwrap();
         let static_fn = Trans::new(config);
         let mut args = HashMap::new();
 
@@ -533,4 +537,26 @@ title = "A title"
         args.insert("lang".to_string(), to_value("fr").unwrap());
         assert_eq!(static_fn.call(&args).unwrap(), "Un titre");
     }
+
+    #[test]
+    fn error_on_absent_translation_lang() {
+        let mut args = HashMap::new();
+        args.insert("lang".to_string(), to_value("absent").unwrap());
+        args.insert("key".to_string(), to_value("title").unwrap());
+
+        let config = Config::parse(TRANS_CONFIG).unwrap();
+        let error = Trans::new(config).call(&args).unwrap_err();
+        assert_eq!("Failed to retreive term translation", format!("{}", error));
+    }
+
+    #[test]
+    fn error_on_absent_translation_key() {
+        let mut args = HashMap::new();
+        args.insert("lang".to_string(), to_value("en").unwrap());
+        args.insert("key".to_string(), to_value("absent").unwrap());
+
+        let config = Config::parse(TRANS_CONFIG).unwrap();
+        let error = Trans::new(config).call(&args).unwrap_err();
+        assert_eq!("Failed to retreive term translation", format!("{}", error));
+    }
 }