Latest nightly doesn't seem to have this optimization

Author: tiaanl

src/size_of_tests.rs

@@ -51,17 +51,20 @@ size_of_test!(parser, crate::parser::Parser, 16);
 size_of_test!(source_position, crate::SourcePosition, 8);
 size_of_test!(parser_state, crate::ParserState, 24);
 
-size_of_test!(basic_parse_error, crate::BasicParseError, if cfg!(rustc_has_better_cow_layout) { 40 } else { 48 });
+size_of_test!(basic_parse_error, crate::BasicParseError, 40);
 size_of_test!(
     parse_error_lower_bound,
     crate::ParseError<()>,
-    if cfg!(rustc_has_better_cow_layout) {
+    if cfg!(rustc_has_pr45225) {
         40
-    } else if cfg!(rustc_has_pr45225) {
-        48
     } else {
         56
     }
 );
 
 size_of_test!(color, crate::Color, 20);
+
+#[test]
+fn asdfk() {
+    println!("{}", std::mem::size_of::<std::borrow::Cow<'static, str>>());
+}