Add helper trait to add context to io errors

lib/src/error.rs

@@ -10,3 +10,9 @@ pub use specialised::*;
 mod critical;
 mod runtime;
 mod specialised;
+
+/// Helper trait to construct specific IO errors from generic ones.
+pub trait SpecificIoError<Output> {
+	/// Add some context to the error or result.
+	fn about(self, context: &'static str) -> Output;
+}

lib/src/error/critical.rs

@@ -4,7 +4,7 @@ use tokio::{sync::mpsc, task::JoinError};
 
 use crate::event::Event;
 
-use super::RuntimeError;
+use super::{RuntimeError, SpecificIoError};
 
 /// Errors which are not recoverable and stop watchexec execution.
 #[derive(Debug, Diagnostic, Error)]
@@ -63,3 +63,18 @@ pub enum CriticalError {
 	#[diagnostic(code(watchexec::critical::internal::missing_handler))]
 	MissingHandler,
 }
+
+impl<T> SpecificIoError<Result<T, CriticalError>> for Result<T, std::io::Error> {
+	fn about(self, context: &'static str) -> Result<T, CriticalError> {
+		self.map_err(|err| err.about(context))
+	}
+}
+
+impl SpecificIoError<CriticalError> for std::io::Error {
+	fn about(self, context: &'static str) -> CriticalError {
+		CriticalError::IoError {
+			about: context,
+			err: self,
+		}
+	}
+}

lib/src/error/runtime.rs

@@ -6,6 +6,8 @@ use tokio::sync::mpsc;
 
 use crate::{event::Event, fs::Watcher, signal::process::SubSignal};
 
+use super::SpecificIoError;
+
 /// Errors which _may_ be recoverable, transient, or only affect a part of the operation, and should
 /// be reported to the user and/or acted upon programatically, but will not outright stop watchexec.
 #[derive(Debug, Diagnostic, Error)]
@@ -225,3 +227,18 @@ pub enum RuntimeError {
 	#[diagnostic(code(watchexec::runtime::set))]
 	Set(#[related] Vec<RuntimeError>),
 }
+
+impl<T> SpecificIoError<Result<T, RuntimeError>> for Result<T, std::io::Error> {
+	fn about(self, context: &'static str) -> Result<T, RuntimeError> {
+		self.map_err(|err| err.about(context))
+	}
+}
+
+impl SpecificIoError<RuntimeError> for std::io::Error {
+	fn about(self, context: &'static str) -> RuntimeError {
+		RuntimeError::IoError {
+			about: context,
+			err: self,
+		}
+	}
+}