Add graceful exit support

lib/src/action.rs

@@ -105,6 +105,9 @@ pub enum Outcome {
 	/// Clear the screen.
 	Clear,
 
+	/// Exit watchexec.
+	Exit,
+
 	/// When command is running, do the first, otherwise the second.
 	IfRunning(Box<Outcome>, Box<Outcome>),
 
@@ -224,6 +227,9 @@ async fn apply_outcome(
 ) -> Result<(), RuntimeError> {
 	match (process.as_mut(), outcome) {
 		(_, Outcome::DoNothing) => {}
+		(_, Outcome::Exit) => {
+			return Err(RuntimeError::Exit);
+		}
 		(Some(p), Outcome::Stop) => {
 			p.kill().await?;
 			p.wait().await?;

lib/src/error.rs

@@ -19,6 +19,11 @@ use crate::{
 #[derive(Debug, Diagnostic, Error)]
 #[non_exhaustive]
 pub enum CriticalError {
+	/// Pseudo-error used to signal a graceful exit.
+	#[error("this should never be printed (exit)")]
+	#[diagnostic(code(watchexec::runtime::exit))]
+	Exit,
+
 	/// A critical I/O error occurred.
 	#[error(transparent)]
 	#[diagnostic(code(watchexec::critical::io_error))]
@@ -36,7 +41,7 @@ pub enum CriticalError {
 
 	/// Error received when a handler is missing on initialisation.
 	///
-	/// This is a critical bug and unlikely to be recoverable in any way.
+	/// This is a **bug** and should be reported.
 	#[error("internal: missing handler on init")]
 	#[diagnostic(code(watchexec::critical::internal::missing_handler))]
 	MissingHandler,
@@ -47,6 +52,11 @@ pub enum CriticalError {
 #[derive(Debug, Diagnostic, Error)]
 #[non_exhaustive]
 pub enum RuntimeError {
+	/// Pseudo-error used to signal a graceful exit.
+	#[error("this should never be printed (exit)")]
+	#[diagnostic(code(watchexec::runtime::exit))]
+	Exit,
+
 	/// Generic I/O error, with no additional context.
 	#[error(transparent)]
 	#[diagnostic(code(watchexec::runtime::io_error))]

lib/src/watchexec.rs

@@ -77,7 +77,10 @@ impl Watchexec {
 
 			let error_hook = subtask!(error_hook, error_hook(er_r, eh));
 
-			try_join!(action, error_hook, fs, signal).map(drop)
+			try_join!(action, error_hook, fs, signal).map(drop).or_else(|e| if matches!(e, CriticalError::Exit) {
+				trace!("got graceful exit request via critical error, erasing the error");
+				Ok(())
+			} else { Err(e) })
 		});
 
 		trace!("done with setup");
@@ -126,6 +129,11 @@ async fn error_hook(
 	mut handler: Box<dyn Handler<RuntimeError> + Send>,
 ) -> Result<(), CriticalError> {
 	while let Some(err) = errors.recv().await {
+		if matches!(err, RuntimeError::Exit) {
+			trace!("got graceful exit request via runtime error, upgrading to crit");
+			return Err(CriticalError::Exit);
+		}
+
 		error!(%err, "runtime error");
 		if let Err(err) = handler.handle(err) {
 			error!(%err, "error while handling error");