feat(error): diagnostic-ify MietteError

src/error.rs

@@ -2,15 +2,30 @@ use std::io;
 
 use thiserror::Error;
 
+use crate::{self as miette, Diagnostic};
+
 /**
 Error enum for miette. Used by certain operations in the protocol.
 */
-#[derive(Debug, Error)]
+#[derive(Debug, Diagnostic, Error)]
 pub enum MietteError {
+    /// Wrapper around [std::io::Error]. This is returned when something went
+    /// wrong while reading a [crate::Source].
     #[error(transparent)]
+    #[diagnostic(code(miette::io_error))]
     IoError(#[from] io::Error),
+
+    /// Returned when a [crate::SourceSpan] extends beyond the bounds of a given [crate::Source].
     #[error("The given offset is outside the bounds of its Source")]
+    #[diagnostic(
+        code(miette::span_out_of_bounds),
+        help("Double-check your spans. Do you have an off-by-one error?")
+    )]
     OutOfBounds,
-    #[error("Failed to install reporter hook")]
-    ReporterInstallFailed,
+
+    /// Returned when installing a [crate::DiagnosticReportPrinter] failed.
+    /// Typically, this will be because [crate::set_printer] was called twice.
+    #[error("Failed to install DiagnosticReportPrinter")]
+    #[diagnostic(code(miette::set_printer_failed))]
+    SetPrinterFailure,
 }

src/printer/mod.rs

@@ -28,7 +28,7 @@ pub fn set_reporter(
 ) -> Result<(), MietteError> {
     REPORTER
         .set(Box::new(reporter))
-        .map_err(|_| MietteError::ReporterInstallFailed)
+        .map_err(|_| MietteError::SetPrinterFailure)
 }
 
 /// Used by [DiagnosticReport] to fetch the reporter that will be used to