refactor(xatu): return structured reports

src/xatu/rules.rs

@@ -4,17 +4,29 @@ use crate::rules::empty_inherit::EmptyInherit;
 
 pub mod empty_inherit;
 
+#[derive(Debug)]
 pub struct Finding {
     pub rule_id: &'static str,
     pub range: ast::SourceRange,
     pub message: &'static str,
 }
 
+#[derive(Debug)]
 pub struct Diagnostic {
     pub file_id: FileId,
     pub finding: Finding,
 }
 
+impl std::fmt::Display for Diagnostic {
+    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            formatter,
+            "{}: {}: {}",
+            self.finding.range, self.finding.rule_id, self.finding.message,
+        )
+    }
+}
+
 pub trait NodeRule {
     type Node;