Implement a new compare_properties implementation of the heading comparison.

src/compare/compare_field.rs

@@ -230,6 +230,45 @@ pub(crate) fn compare_property_boolean<'b, 's, 'x, R, RG: Fn(R) -> bool>(
     }
 }
 
+pub(crate) fn compare_property_single_ast_node<
+    'b,
+    's,
+    'x: 'b + 's,
+    R,
+    RV: std::fmt::Debug,
+    RG: Fn(R) -> Option<RV>,
+>(
+    source: &'s str,
+    emacs: &'b Token<'s>,
+    rust_node: R,
+    emacs_field: &'x str,
+    rust_value_getter: RG,
+) -> Result<ComparePropertiesResult<'b, 's>, Box<dyn std::error::Error>>
+where
+    AstNode<'b, 's>: From<RV>,
+{
+    let value = get_property(emacs, emacs_field)?;
+    let rust_value = rust_value_getter(rust_node);
+    match (value, rust_value) {
+        (None, None) => {}
+        (None, rv @ Some(_)) | (Some(_), rv @ None) => {
+            let this_status = DiffStatus::Bad;
+            let message = Some(format!(
+                "{} mismatch (emacs != rust) {:?} != {:?}",
+                emacs_field, value, rv
+            ));
+            return Ok(ComparePropertiesResult::SelfChange(this_status, message));
+        }
+        (Some(ev), Some(rv)) => {
+            let child_status: Vec<DiffEntry<'b, 's>> =
+                vec![compare_ast_node(source, ev, rv.into())?];
+            let diff_scope = artificial_diff_scope(emacs_field, child_status)?;
+            return Ok(ComparePropertiesResult::DiffEntry(diff_scope));
+        }
+    }
+    Ok(ComparePropertiesResult::NoChange)
+}
+
 pub(crate) fn compare_property_list_of_ast_nodes<
     'b,
     's,