feat(protocol): Make usafe of ? and return types with Diagnostics mor…

…e ergonomic

src/protocol.rs

@@ -12,7 +12,7 @@ use crate::MietteError;
 Adds rich metadata to your Error that can be used by [DiagnosticReporter] to print
 really nice and human-friendly error messages.
 */
-pub trait Diagnostic: std::error::Error + Send + Sync {
+pub trait Diagnostic: std::error::Error {
     /// Unique diagnostic code that can be used to look up more information
     /// about this Diagnostic. Ideally also globally unique, and documented in
     /// the toplevel crate's documentation for easy searching. Rust path
@@ -37,6 +37,14 @@ pub trait Diagnostic: std::error::Error + Send + Sync {
     }
 }
 
+impl std::error::Error for Box<dyn Diagnostic> {}
+
+impl<T: Diagnostic + 'static> From<T> for Box<dyn Diagnostic> {
+    fn from(diag: T) -> Self {
+        Box::new(diag)
+    }
+}
+
 /**
 Protocol for [Diagnostic] handlers, which are responsible for actually printing out Diagnostics.