Add context to last critical io error

and remove generic critical io error enum variant

lib/src/error/critical.rs

@@ -24,12 +24,7 @@ pub enum CriticalError {
 	#[diagnostic(code(watchexec::critical::external))]
 	External(#[from] Box<dyn std::error::Error + Send + Sync>),
 
-	/// A critical I/O error occurred (generic).
-	#[error("io(unspecified): {0}")]
-	#[diagnostic(code(watchexec::critical::io_error_generic))]
-	IoErrorGeneric(#[from] std::io::Error),
-
-	/// A critical I/O error occurred (specific).
+	/// A critical I/O error occurred.
 	#[error("io({about}): {err}")]
 	#[diagnostic(code(watchexec::critical::io_error))]
 	IoError {

lib/src/signal/source.rs

@@ -106,7 +106,9 @@ async fn imp_worker(
 	macro_rules! listen {
 		($sig:ident) => {{
 			trace!(kind=%stringify!($sig), "listening for unix signal");
-			signal(SignalKind::$sig())?
+			signal(SignalKind::$sig()).map_err(|err| CriticalError::IoError {
+			about: concat!("setting ", stringify!($sig), " signal listener"), err
+		})?
 		}}
 	}