Improve composition diagnostics

crates/decodal-cli/src/main.rs

@@ -148,6 +148,15 @@ fn print_diagnostic(error: &Diagnostic) {
         end = error.span.end,
         message = error.message,
     );
+    for label in &error.labels {
+        eprintln!(
+            "  note {source}:{start}..{end}: {message}",
+            source = label.span.source.0,
+            start = label.span.start,
+            end = label.span.end,
+            message = label.message,
+        );
+    }
 }
 
 fn print_data(data: &Data, indent: usize) {