Inline some niche RustName methods
diff --git a/syntax/check.rs b/syntax/check.rs
index d0b0ba0..2ac800b 100644
--- a/syntax/check.rs
+++ b/syntax/check.rs
@@ -356,7 +356,7 @@
     if let Some(receiver) = &efn.receiver {
         let ref span = span_for_receiver_error(receiver);
 
-        if receiver.ty.is_self() {
+        if receiver.ty.rust == "Self" {
             let mutability = match receiver.mutable {
                 true => "mut ",
                 false => "",