Add runtime language configuration (#1794)

* Add set-language typable command to change the language of current buffer.
* Add completer for available language options.

helix-core/src/syntax.rs

@@ -537,6 +537,10 @@ impl Loader {
         None
     }
 
+    pub fn language_configs(&self) -> impl Iterator<Item = &Arc<LanguageConfiguration>> {
+        self.language_configs.iter()
+    }
+
     pub fn set_scopes(&self, scopes: Vec<String>) {
         self.scopes.store(Arc::new(scopes));
 

helix-term/src/commands/typed.rs

@@ -913,6 +913,29 @@ fn setting(
     Ok(())
 }
 
+/// Change the language of the current buffer at runtime.
+fn language(
+    cx: &mut compositor::Context,
+    args: &[Cow<str>],
+    _event: PromptEvent,
+) -> anyhow::Result<()> {
+    if args.len() != 1 {
+        anyhow::bail!("Bad arguments. Usage: `:set-language language`");
+    }
+
+    let doc = doc_mut!(cx.editor);
+    let loader = Some(cx.editor.syn_loader.clone());
+    let config = cx.editor.syn_loader.language_configs().find_map(|config| {
+        if &config.language_id == &args[0] {
+            Some(config.clone())
+        } else {
+            None
+        }
+    });
+    doc.set_language(config, loader);
+    Ok(())
+}
+
 fn sort(
     cx: &mut compositor::Context,
     args: &[Cow<str>],
@@ -1376,6 +1399,13 @@ pub const TYPABLE_COMMAND_LIST: &[TypableCommand] = &[
             fun: goto_line_number,
             completer: None,
         },
+        TypableCommand {
+            name: "set-language",
+            aliases: &["lang"],
+            doc: "Set the language of current buffer.",
+            fun: language,
+            completer: Some(completers::language),
+        },
         TypableCommand {
             name: "set-option",
             aliases: &["set"],

helix-term/src/ui/mod.rs

@@ -284,6 +284,27 @@ pub mod completers {
         })
     }
 
+    pub fn language(editor: &Editor, input: &str) -> Vec<Completion> {
+        let matcher = Matcher::default();
+
+        let mut matches: Vec<_> = editor
+            .syn_loader
+            .language_configs()
+            .filter_map(|config| {
+                matcher
+                    .fuzzy_match(&config.language_id, input)
+                    .map(|score| (config.language_id.clone(), score))
+            })
+            .collect();
+
+        matches.sort_unstable_by_key(|(_language, score)| Reverse(*score));
+
+        matches
+            .into_iter()
+            .map(|(language, _score)| ((0..), language.into()))
+            .collect()
+    }
+
     pub fn directory(_editor: &Editor, input: &str) -> Vec<Completion> {
         filename_impl(input, |entry| {
             let is_dir = entry.file_type().map_or(false, |entry| entry.is_dir());