list available languages + better error reporting

src/install.rs

@@ -18,15 +18,32 @@ pub struct Install {
     #[arg(short, long)]
     force: bool,
 
+    /// List installable parsers
+    #[arg(short, long)]
+    list: bool,
+
     languages: Vec<String>,
 }
 
 impl Install {
     pub fn run(self, mut settings: Settings) -> anyhow::Result<ExitCode> {
+        let language_defs = settings.language_defs()?;
+
+        if self.list {
+            let mut available = language_defs.into_keys().collect::<Vec<_>>();
+            available.sort();
+            available.dedup();
+
+            for language in available {
+                println!("{language}");
+            }
+
+            return Ok(ExitCode::SUCCESS);
+        }
+
         let src_dir = tempdir()?;
 
         let parser_dir = settings.parser_dir();
-        let language_defs = settings.language_defs()?;
         let InstallSettings { compiler } = settings.install;
 
         create_dir_all(&parser_dir)?;
@@ -37,6 +54,7 @@ impl Install {
         let Self {
             mut languages,
             force,
+            ..
         } = self;
 
         languages.sort();

src/install/languages.rs

@@ -16,6 +16,10 @@ pub type LanguageDefs = HashMap<String, InstallInfo>;
 pub struct LanguageDb(Vec<LanguageDefs>);
 
 impl LanguageDb {
+    pub fn new(sources: Vec<HashMap<String, InstallInfo>>) -> Self {
+        Self(sources)
+    }
+
     pub fn get(&self, language: &str) -> Option<&InstallInfo> {
         for source in &self.0 {
             if let Some(info) = source.get(language) {
@@ -25,8 +29,8 @@ impl LanguageDb {
         None
     }
 
-    pub fn new(sources: Vec<HashMap<String, InstallInfo>>) -> Self {
+    pub fn into_keys(self) -> impl Iterator<Item = String> {
-        Self(sources)
+        self.0.into_iter().flat_map(HashMap::into_keys)
     }
 }
 

src/settings.rs

@@ -56,12 +56,15 @@ pub enum Error {
     #[error("unable to read config file: {0}")]
     Io(#[from] io::Error),
 
-    #[error(transparent)]
+    #[error("{file:?}: {e}")]
-    Toml(#[from] toml::de::Error),
+    Toml { file: PathBuf, e: toml::de::Error },
 }
 
 pub fn get_settings(path: &Path) -> Result<Settings, Error> {
-    Ok(toml::from_str(&read_to_string(path)?)?)
+    toml::from_str(&read_to_string(path)?).map_err(|e| Error::Toml {
+        file: path.to_owned(),
+        e,
+    })
 }
 
 impl Settings {
@@ -76,7 +79,12 @@ impl Settings {
         let default_path = self.data_dir.join("languages.toml");
 
         match read_to_string(&default_path) {
-            Ok(default_defs) => sources.push(toml::from_str(&default_defs)?),
+            Ok(default_defs) => {
+                sources.push(toml::from_str(&default_defs).map_err(|e| Error::Toml {
+                    file: default_path,
+                    e,
+                })?)
+            }
             Err(e) => warning!("couldn't read language install info from {default_path:?}: {e}"),
         }