Add docs for error_handler as it's a bit tricky

lib/src/config.rs

@@ -47,7 +47,17 @@ pub struct InitConfig {
 	/// If the handler errors, [_that_ error][crate::error::RuntimeError::Handler] is immediately
 	/// given to the handler. If that second handler call errors as well, its error is ignored.
 	///
-	/// Only used at construction time, cannot be changed via reconfiguration.
+	/// # Examples
+	///
+	/// ```
+	/// # use std::convert::Infallible;
+	/// # use watchexec::config::InitConfigBuilder;
+	/// InitConfigBuilder::default()
+	///     .error_handler(Box::new(|err| async move {
+	///         tracing::error!("{}", err);
+	///         Ok::<(), Infallible>(())
+	///     }));
+	/// ```
 	#[builder(default = "Box::new(()) as _")]
 	pub error_handler: Box<dyn Handler<RuntimeError> + Send>,
 

lib/src/handler.rs

@@ -162,7 +162,7 @@ where
 
 impl<T> Handler<T> for () {
 	fn handle(&mut self, _data: T) -> Result<(), Box<dyn Error>> {
-		Ok(()).map_err(|e: std::convert::Infallible| Box::new(e) as _)
+		Ok::<(), std::convert::Infallible>(()).map_err(|e| Box::new(e) as _)
 	}
 }
 

lib/src/lib.rs

@@ -16,10 +16,10 @@
 //!
 //! #[tokio::main]
 //! async fn main() {
-//!     let init = InitConfigBuilder::new()
+//!     let init = InitConfigBuilder::default()
 //!         .error_handler(PrintDebug(std::io::stderr()));
 //!
-//!     let mut runtime = RuntimeConfigBuilder::new()
+//!     let mut runtime = RuntimeConfigBuilder::default()
 //!     config.pathset(["watchexec.conf"]);
 //!
 //!     let conf = YourConfigFormat::load_from_file("watchexec.conf").await?;
@@ -62,11 +62,11 @@ pub mod command;
 pub mod error;
 pub mod event;
 pub mod fs;
-pub mod handler;
 pub mod signal;
 
 // the core experience
 pub mod config;
+pub mod handler;
 mod watchexec;
 
 #[doc(inline)]

lib/src/watchexec.rs

@@ -70,7 +70,7 @@ impl Watchexec {
 
 			let error_hook = subtask!(error_hook(er_r, eh));
 
-			try_join!(action, fs, signal).map(drop)
+			try_join!(action, error_hook, fs, signal).map(drop)
 		});
 
 		Ok(Arc::new(Self {

lib/tests/error_handler.rs

@@ -0,0 +1,31 @@
+use std::time::Duration;
+
+use tokio::time::sleep;
+use watchexec::{
+	config::{InitConfigBuilder, RuntimeConfigBuilder},
+	Watchexec,
+};
+
+#[tokio::main]
+async fn main() -> color_eyre::eyre::Result<()> {
+	tracing_subscriber::fmt::init();
+	color_eyre::install()?;
+
+	let init = InitConfigBuilder::default()
+		.error_handler(Box::new(|err| async move {
+			eprintln!("Watchexec Runtime Error: {}", err);
+			Ok::<(), std::convert::Infallible>(())
+		}))
+		.build()?;
+
+	let runtime = RuntimeConfigBuilder::default().build()?;
+
+	let wx = Watchexec::new(init, runtime)?;
+	wx.main();
+
+	// TODO: induce an error here
+
+	sleep(Duration::from_secs(1)).await;
+
+	Ok(())
+}