Add --auto-next flag to skip the post-success prompt in watch mode

After passing an exercise, the watch loop currently waits for `n`
before advancing. Add an opt-in `--auto-next` flag that renders the
"Exercise done" screen for ~1.5s, then auto-advances to the next
pending exercise and runs it. Auto-advance only fires on success; a
failing exercise still stops at the prompt.

The `n:next` key is hidden from the prompt when --auto-next is on,
but the user can still press `n` to skip ahead manually. --auto-next
is compatible with --manual-run: pressing `r` triggers a check, and
on success the loop auto-advances the same way.

CHANGELOG.md

@@ -8,6 +8,7 @@
 - Automatically open the current file with `$EDITOR` in a new pane if Rustlings is running in [Zellij](https://zellij.dev)
 - New argument `--no-editor` to disable automatic opening of the current file in VS Code or Zellij
 - New argument `--edit-cmd` to communicate with an editor running in a different process to open the current exercise
+- New argument `--auto-next` to automatically move on to the next pending exercise after it passes, without waiting for `n`
 - Show the file link of the current exercise when running `rustlings hint` and `rustlings reset`
 
 ### Fixed

src/cli.rs

@@ -26,6 +26,10 @@ pub struct Args {
     /// Only use this if Rustlings fails to detect exercise file changes
     #[arg(long)]
     pub manual_run: bool,
+    /// Automatically move on to the next pending exercise after it passes,
+    /// without waiting for `n`. Useful for learners who want a continuous flow.
+    #[arg(long)]
+    pub auto_next: bool,
 }
 
 #[derive(Subcommand)]

src/main.rs

@@ -118,7 +118,7 @@ fn main() -> Result<ExitCode> {
                 )
             };
 
-            watch::watch(&mut app_state, notify_exercise_names)?;
+            watch::watch(&mut app_state, notify_exercise_names, args.auto_next)?;
             app_state.close_editor()?;
         }
         Some(Command::Run { name }) => {

src/watch.rs

@@ -59,6 +59,7 @@ enum WatchExit {
 fn run_watch(
     app_state: &mut AppState,
     notify_exercise_names: Option<&'static [&'static [u8]]>,
+    auto_next: bool,
 ) -> Result<WatchExit> {
     let (watch_event_sender, watch_event_receiver) = channel();
 
@@ -87,7 +88,7 @@ fn run_watch(
         None
     };
 
-    let mut watch_state = WatchState::build(app_state, watch_event_sender, manual_run)?;
+    let mut watch_state = WatchState::build(app_state, watch_event_sender, manual_run, auto_next)?;
     let mut stdout = io::stdout().lock();
 
     watch_state.run_current_exercise(&mut stdout)?;
@@ -133,9 +134,10 @@ fn run_watch(
 fn watch_list_loop(
     app_state: &mut AppState,
     notify_exercise_names: Option<&'static [&'static [u8]]>,
+    auto_next: bool,
 ) -> Result<()> {
     loop {
-        match run_watch(app_state, notify_exercise_names)? {
+        match run_watch(app_state, notify_exercise_names, auto_next)? {
             WatchExit::Shutdown => break Ok(()),
             // It is much easier to exit the watch mode, launch the list mode and then restart
             // the watch mode instead of trying to pause the watch threads and correct the
@@ -149,6 +151,7 @@ fn watch_list_loop(
 pub fn watch(
     app_state: &mut AppState,
     notify_exercise_names: Option<&'static [&'static [u8]]>,
+    auto_next: bool,
 ) -> Result<()> {
     // TODO: Use cfg_select! after bumping MSRV to at least 1.95
     #[cfg(not(windows))]
@@ -161,7 +164,7 @@ pub fn watch(
             rustix::termios::LocalModes::ICANON | rustix::termios::LocalModes::ECHO;
         rustix::termios::tcsetattr(stdin_fd, rustix::termios::OptionalActions::Now, &termios)?;
 
-        let res = watch_list_loop(app_state, notify_exercise_names);
+        let res = watch_list_loop(app_state, notify_exercise_names, auto_next);
 
         termios.local_modes = original_local_modes;
         rustix::termios::tcsetattr(stdin_fd, rustix::termios::OptionalActions::Now, &termios)?;
@@ -170,7 +173,7 @@ pub fn watch(
     }
 
     #[cfg(windows)]
-    watch_list_loop(app_state, notify_exercise_names)
+    watch_list_loop(app_state, notify_exercise_names, auto_next)
 }
 
 const QUIT_MSG: &[u8] = b"q\n

src/watch/state.rs

@@ -10,6 +10,7 @@ use std::{
     io::{self, Read, StdoutLock, Write},
     sync::mpsc::{Sender, SyncSender, sync_channel},
     thread,
+    time::Duration,
 };
 
 use crate::{
@@ -24,6 +25,9 @@ const HEADING_ATTRIBUTES: Attributes = Attributes::none()
     .with(Attribute::Bold)
     .with(Attribute::Underlined);
 
+// How long to show the "Exercise done" screen before auto-advancing.
+const AUTO_NEXT_DELAY: Duration = Duration::from_millis(1500);
+
 #[derive(PartialEq, Eq)]
 enum DoneStatus {
     DoneWithSolution(String),
@@ -37,6 +41,7 @@ pub struct WatchState<'a> {
     show_hint: bool,
     done_status: DoneStatus,
     manual_run: bool,
+    auto_next: bool,
     term_width: u16,
     terminal_event_unpause_sender: SyncSender<()>,
 }
@@ -46,6 +51,7 @@ impl<'a> WatchState<'a> {
         app_state: &'a mut AppState,
         watch_event_sender: Sender<WatchEvent>,
         manual_run: bool,
+        auto_next: bool,
     ) -> Result<Self> {
         let term_width = terminal::size()
             .context("Failed to get the terminal size")?
@@ -69,6 +75,7 @@ impl<'a> WatchState<'a> {
             show_hint: false,
             done_status: DoneStatus::Pending,
             manual_run,
+            auto_next,
             term_width,
             terminal_event_unpause_sender,
         })
@@ -110,8 +117,21 @@ impl<'a> WatchState<'a> {
         self.app_state.join_editor_handle(editor_handle)?;
         self.render(stdout)?;
 
+        // If `--auto-next` is on and the exercise passed, briefly show the
+        // "done" screen, then advance to the next pending exercise and run it.
+        // The recursion bottoms out when we hit a failing exercise
+        // (rendering leaves the user at the prompt) or when everything is done.
+        if self.auto_next && self.done_status != DoneStatus::Pending {
+            thread::sleep(AUTO_NEXT_DELAY);
+            match self.next_exercise(stdout)? {
+                ExercisesProgress::AllDone => Ok(()),
+                ExercisesProgress::NewPending => self.run_current_exercise(stdout),
+                ExercisesProgress::CurrentPending => Ok(()),
+            }
+        } else {
             Ok(())
         }
+    }
 
     pub fn reset_exercise(&mut self, stdout: &mut StdoutLock) -> Result<()> {
         clear_terminal(stdout)?;
@@ -175,7 +195,7 @@ impl<'a> WatchState<'a> {
     }
 
     fn show_prompt(&self, stdout: &mut StdoutLock) -> io::Result<()> {
-        if self.done_status != DoneStatus::Pending {
+        if !self.auto_next && self.done_status != DoneStatus::Pending {
             stdout.queue(SetAttribute(Attribute::Bold))?;
             stdout.write_all(b"n")?;
             stdout.queue(ResetColor)?;