Make a more generic version of compare_property_quoted_string.

This allows for the rust value to be determined by a function rather than hard-coded.

src/compare/compare_field.rs

@@ -1,3 +1,5 @@
+use std::fmt::Debug;
+
 use super::diff::DiffStatus;
 use super::sexp::Token;
 use super::util::get_property_quoted_string;
@@ -5,9 +7,22 @@ use super::util::get_property_quoted_string;
 #[derive(Debug)]
 pub(crate) enum EmacsField<'s> {
     Required(&'s str),
+    #[allow(dead_code)]
     Optional(&'s str),
 }
 
+/// Do no comparison.
+///
+/// This is for when you want to acknowledge that a field exists in the emacs token, but you do not have any validation for it when using the compare_properties!() macro. Ideally, this should be kept to a minimum since this represents untested values.
+#[allow(dead_code)]
+pub(crate) fn compare_noop<'b, 's, 'x>(
+    _emacs: &'b Token<'s>,
+    _emacs_field: &'x str,
+    _rust_value: (),
+) -> Result<Option<(DiffStatus, Option<String>)>, Box<dyn std::error::Error>> {
+    Ok(None)
+}
+
 pub(crate) fn compare_property_quoted_string_required_value<'b, 's, 'x>(
     emacs: &'b Token<'s>,
     emacs_field: &'x str,
@@ -25,3 +40,30 @@ pub(crate) fn compare_property_quoted_string_required_value<'b, 's, 'x>(
         Ok(None)
     }
 }
+
+pub(crate) fn compare_property_quoted_string<
+    'b,
+    's,
+    'x,
+    R,
+    RV: Debug + for<'a> PartialEq<Option<&'a str>>,
+    RG: Fn(R) -> RV,
+>(
+    emacs: &'b Token<'s>,
+    emacs_field: &'x str,
+    rust_node: R,
+    rust_value_getter: RG,
+) -> Result<Option<(DiffStatus, Option<String>)>, Box<dyn std::error::Error>> {
+    let value = get_property_quoted_string(emacs, emacs_field)?;
+    let rust_value = rust_value_getter(rust_node);
+    if !rust_value.eq(&value.as_ref().map(String::as_str)) {
+        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)
+    }
+}