use Reverse instead of manually doing reverse comparison

Author: yotamofek

compiler/rustc_resolve/src/diagnostics.rs

@@ -1,3 +1,5 @@
+use std::cmp::Reverse;
+
 use rustc_ast::expand::StrippedCfgItem;
 use rustc_ast::ptr::P;
 use rustc_ast::visit::{self, Visitor};
@@ -2357,7 +2359,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         // 2) `std` suggestions before `core` suggestions.
         let mut extern_crate_names =
             self.extern_prelude.keys().map(|ident| ident.name).collect::<Vec<_>>();
-        extern_crate_names.sort_by(|a, b| b.as_str().partial_cmp(a.as_str()).unwrap());
+        extern_crate_names.sort_by_key(|&name| Reverse(name));
 
         for name in extern_crate_names.into_iter() {
             // Replace first ident with a crate name and check if that is valid.