Elevate FsWatcherCreate errors to critical

See #251

cli/src/config/init.rs

@@ -3,28 +3,33 @@ use std::convert::Infallible;
 use clap::ArgMatches;
 use miette::{Report, Result};
 use tracing::error;
-use watchexec::{config::InitConfig, error::RuntimeError, handler::SyncFnHandler};
+use watchexec::{config::InitConfig, error::RuntimeError, handler::SyncFnHandler, ErrorHook};
 
 pub fn init(_args: &ArgMatches<'static>) -> Result<InitConfig> {
 	let mut config = InitConfig::default();
 	config.on_error(SyncFnHandler::from(
-		|data| -> std::result::Result<(), Infallible> {
+		|err: ErrorHook| -> std::result::Result<(), Infallible> {
 			if let RuntimeError::IoError {
 				about: "waiting on process group",
 				..
-			} = data
+			} = err.error
 			{
 				// "No child processes" and such
 				// these are often spurious, so condemn them to -v only
-				error!("{}", data);
+				error!("{}", err.error);
+				return Ok(());
+			}
+
+			if let RuntimeError::FsWatcherCreate { .. } = err.error {
+				err.elevate();
 				return Ok(());
 			}
 
 			if cfg!(debug_assertions) {
-				eprintln!("[[{:?}]]", data);
+				eprintln!("[[{:?}]]", err.error);
 			}
 
-			eprintln!("[[Error (not fatal)]]\n{}", Report::new(data));
+			eprintln!("[[Error (not fatal)]]\n{}", Report::new(err.error));
 
 			Ok(())
 		},

lib/src/error/critical.rs

@@ -24,6 +24,15 @@ pub enum CriticalError {
 	#[diagnostic(code(watchexec::critical::external))]
 	External(#[from] Box<dyn std::error::Error + Send + Sync>),
 
+	/// For elevated runtime errors.
+	///
+	/// This should be used for runtime errors elevated to critical. This currently does not happen
+	/// in watchexec, but it is possible in the future. This variant is useful with the `on_error`
+	/// runtime error handler; see [`ErrorHook`](crate::ErrorHook).
+	#[error("elevated: {0}")]
+	#[diagnostic(code(watchexec::critical::elevated_runtime))]
+	Elevated(#[source] RuntimeError),
+
 	/// A critical I/O error occurred.
 	#[error("io({about}): {err}")]
 	#[diagnostic(code(watchexec::critical::io_error))]

lib/src/watchexec.rs

@@ -250,4 +250,12 @@ impl ErrorHook {
 	pub fn critical(self, critical: CriticalError) {
 		self.critical.set(critical).ok();
 	}
+
+	/// Elevate the current runtime error to critical.
+	///
+	/// This is a shorthand method for `ErrorHook::critical(CriticalError::Elevated(error))`.
+	pub fn elevate(self) {
+		let Self { error, critical } = self;
+		critical.set(CriticalError::Elevated(error)).ok();
+	}
 }