feat(xatu): report diagnostic line ranges

src/xatu/rules.rs

@@ -27,8 +27,8 @@ 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,
+            "{}: {}",
+            self.finding.rule_id, self.finding.message
         )
     }
 }

src/xatu/xatu.rs

@@ -25,13 +25,33 @@ impl std::fmt::Display for Report {
     fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         for diagnostic in &self.diagnostics {
             let file = self.files.get(diagnostic.file_id);
-            writeln!(formatter, "{}:{diagnostic}", file.path.display())?;
+            let (start, end) = line_range(&file.source, diagnostic.finding.range);
+            writeln!(
+                formatter,
+                "{}:{start}..{end}:{diagnostic}",
+                file.path.display()
+            )?;
         }
 
         Ok(())
     }
 }
 
+fn line_range(source: &str, range: ast::SourceRange) -> (usize, usize) {
+    let line_at = |offset| {
+        source
+            .bytes()
+            .take(offset)
+            .filter(|byte| *byte == b'\n')
+            .count()
+            + 1
+    };
+    let start = line_at(range.start);
+    let end = line_at(range.end);
+
+    (start, end)
+}
+
 /// Analyzes source files and returns the diagnostics Xatu finds.
 pub fn future_sight(files: Vec<SourceFile>) -> status::Result<Report> {
     let mut store = FileStore::default();