Use Symbol equality in check_ident_token.

Author: nnethercote

src/librustc_lint/builtin.rs

@@ -1439,8 +1439,8 @@ impl KeywordIdents {
     {
         let next_edition = match cx.sess.edition() {
             Edition::Edition2015 => {
-                match &ident.as_str()[..] {
-                    "async" | "await" | "try" => Edition::Edition2018,
+                match ident.name {
+                    kw::Async | kw::Await | kw::Try => Edition::Edition2018,
 
                     // rust-lang/rust#56327: Conservatively do not
                     // attempt to report occurrences of `dyn` within
@@ -1454,7 +1454,7 @@ impl KeywordIdents {
                     // its precise role in the parsed AST and thus are
                     // assured this is truly an attempt to use it as
                     // an identifier.
-                    "dyn" if !under_macro => Edition::Edition2018,
+                    kw::Dyn if !under_macro => Edition::Edition2018,
 
                     _ => return,
                 }