Assume :standard-properties is an expected field.

src/compare/compare_field.rs

@@ -0,0 +1,27 @@
+use super::diff::DiffStatus;
+use super::sexp::Token;
+use super::util::get_property_quoted_string;
+
+#[derive(Debug)]
+pub(crate) enum EmacsField<'s> {
+    Required(&'s str),
+    Optional(&'s str),
+}
+
+pub(crate) fn compare_property_quoted_string_required_value<'b, 's, 'x>(
+    emacs: &'b Token<'s>,
+    emacs_field: &'x str,
+    rust_value: &'s str,
+) -> Result<Option<(DiffStatus, Option<String>)>, Box<dyn std::error::Error>> {
+    let value = get_property_quoted_string(emacs, emacs_field)?;
+    if value.as_ref().map(String::as_str) != Some(rust_value) {
+        let this_status = DiffStatus::Bad;
+        let message = Some(format!(
+            "{} mismatch (emacs != rust) {:?} != {:?}",
+            emacs_field, value, rust_value
+        ));
+        Ok(Some((this_status, message)))
+    } else {
+        Ok(None)
+    }
+}