Nevermind, it did work.

src/compare/compare_field.rs

@@ -1,12 +1,11 @@
-use std::borrow::Cow;
 use std::collections::BTreeSet;
 use std::fmt::Debug;
 use std::str::FromStr;
 
 use super::diff::artificial_diff_scope;
+use super::diff::artificial_owned_diff_scope;
 use super::diff::compare_ast_node;
 use super::diff::DiffEntry;
-use super::diff::DiffLayer;
 use super::diff::DiffStatus;
 use super::sexp::unquote;
 use super::sexp::Token;
@@ -422,7 +421,7 @@ where
 pub(crate) fn compare_property_list_of_list_of_list_of_ast_nodes<
     'b,
     's,
-    'x: 'b + 's,
+    'x,
     R,
     RG: Fn(R) -> Option<&'b Vec<Vec<Object<'s>>>>,
 >(
@@ -481,12 +480,8 @@ pub(crate) fn compare_property_list_of_list_of_list_of_ast_nodes<
         for (e, r) in value.iter().zip(rust_value) {
             child_status.push(compare_ast_node(source, e, r.into())?);
         }
-        let diff_scope = DiffLayer {
+        let diff_scope = artificial_owned_diff_scope(emacs_field, child_status)?;
-            name: Cow::Owned(emacs_field.to_string()),
+        return Ok(ComparePropertiesResult::DiffEntry(diff_scope));
-            children: child_status,
-        };
-        // let diff_scope = artificial_diff_scope(emacs_field, child_status)?;
-        return Ok(ComparePropertiesResult::DiffEntry(diff_scope.into()));
     }
     Ok(ComparePropertiesResult::NoChange)
 }

src/compare/diff.rs

@@ -331,6 +331,17 @@ pub(crate) fn artificial_diff_scope<'b, 's>(
     .into())
 }
 
+pub(crate) fn artificial_owned_diff_scope<'b, 's, 'x>(
+    name: &'x str,
+    children: Vec<DiffEntry<'b, 's>>,
+) -> Result<DiffEntry<'b, 's>, Box<dyn std::error::Error>> {
+    Ok(DiffLayer {
+        name: name.to_string().into(),
+        children,
+    }
+    .into())
+}
+
 pub(crate) fn compare_ast_node<'b, 's>(
     source: &'s str,
     emacs: &'b Token<'s>,