feat: cycle command completions with Tab

src/editor.rs

@@ -805,6 +805,11 @@ core_actions![
         Action::Submit,
         &[Mode::Command, Mode::Search],
     ),
+    (
+        "core.command_complete",
+        Action::CommandComplete,
+        &[Mode::Command],
+    ),
     (
         "core.palette",
         Action::Palette,
@@ -1584,6 +1589,10 @@ fn default_bindings() -> HashMap<Mode, HashMap<Input, Binding>> {
                 .insert(key, Binding::Action(action));
         }
     }
+    bindings
+        .entry(Mode::Command)
+        .or_default()
+        .insert(Input::Char('\t'), Binding::Action(CommandComplete));
     for mode in [Mode::Command, Mode::Search] {
         for (key, action) in [(Input::Up, Up), (Input::Ctrl('k'), Up), (Input::Down, Down)] {
             bindings
@@ -1751,6 +1760,7 @@ struct ViewState {
     search_highlight: bool,
     search_match: Option<SearchMatch>,
     command_line: String,
+    command_completion_prefix: Option<String>,
     prompt_history_index: Option<usize>,
     prompt_draft: String,
     command_from_visual: bool,
@@ -1775,6 +1785,7 @@ impl ViewState {
             search_highlight: false,
             search_match: None,
             command_line: String::new(),
+            command_completion_prefix: None,
             prompt_history_index: None,
             prompt_draft: String::new(),
             command_from_visual: false,
@@ -1799,6 +1810,7 @@ impl ViewState {
             search_highlight: self.search_highlight,
             search_match: self.search_match,
             command_line: self.command_line.clone(),
+            command_completion_prefix: self.command_completion_prefix.clone(),
             prompt_history_index: self.prompt_history_index,
             prompt_draft: self.prompt_draft.clone(),
             command_from_visual: self.command_from_visual,
@@ -8006,6 +8018,12 @@ impl Editor {
 
     fn handle_input(&mut self, input: Input) -> Option<Invocation> {
         let mode = self.binding_mode();
+        if !matches!(
+            self.bindings.get(&mode).and_then(|keys| keys.get(&input)),
+            Some(Binding::Action(Action::CommandComplete))
+        ) {
+            self.active.view.command_completion_prefix = None;
+        }
         if self.completion.is_some() && (self.diff().is_none() || self.diff_editing()) {
             let request = matches!(
                 self.bindings
@@ -8419,6 +8437,37 @@ impl Editor {
         self.active.view.mode = Mode::Command;
     }
 
+    fn complete_command(&mut self) {
+        let view = &mut self.active.view;
+        let command = view.command_line.trim_start();
+        let name = command.strip_prefix(':').unwrap_or(command);
+        if name.contains(char::is_whitespace) {
+            return;
+        }
+        let start = view.command_line.len() - name.len();
+        let cycling = view.command_completion_prefix.is_some();
+        let prefix = view
+            .command_completion_prefix
+            .get_or_insert_with(|| name.to_owned());
+        let mut first = None;
+        let mut next = None;
+        for candidate in self.features.values().flat_map(|feature| &feature.commands) {
+            let candidate = candidate.as_str();
+            if !candidate.starts_with(prefix.as_str()) {
+                continue;
+            }
+            if first.is_none_or(|first| candidate < first) {
+                first = Some(candidate);
+            }
+            if cycling && candidate > name && next.is_none_or(|next| candidate < next) {
+                next = Some(candidate);
+            }
+        }
+        if let Some(candidate) = next.or(first) {
+            view.command_line.replace_range(start.., candidate);
+        }
+    }
+
     fn navigate_prompt_history(&mut self, previous: bool) {
         let history = if self.active.view.mode == Mode::Search {
             &self.search_history
@@ -8514,6 +8563,7 @@ impl Editor {
         let count = self.count.take().unwrap_or(1);
         self.clear_sequence();
         match action {
+            Action::CommandComplete => self.complete_command(),
             Action::SnippetNext => {
                 if self.snippet.is_some() {
                     self.navigate_snippet(true);

src/main.rs

@@ -57,6 +57,7 @@ Insert: Ctrl+n requests LSP completion at primary caret, then cycles next; Ctrl+
         Outside snippets Enter inserts newline, Tab inserts a tab or configured spaces; Esc returns to Normal
 Insert/Command/Search: Ctrl+u deletes backward to the logical line start
 Command/Search: Up/Ctrl+k older history; Down/Ctrl+j newer history or unfinished input; Enter submits
+Command: Tab completes command names; repeated presses cycle alphabetical matches (not arguments)
 Search: Enter accepts current/next literal match, Esc cancels (case-sensitive, wraps)
 Commands: :save [PATH], :force_save [PATH], :quit, :force_quit,
           :save_and_quit [PATH], :force_save_and_quit [PATH], :plugins, :PLUGIN [ARGS]