Convert sort_by to sort_by_cached_key

src/librustc_driver/lib.rs

@@ -23,6 +23,7 @@
 #![cfg_attr(unix, feature(libc))]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
+#![feature(slice_sort_by_cached_key)]
 #![feature(set_stdio)]
 #![feature(rustc_stack_internals)]
 
@@ -83,7 +84,6 @@
 use serialize::json::ToJson;
 
 use std::any::Any;
-use std::cmp::Ordering::Equal;
 use std::cmp::max;
 use std::default::Default;
 use std::env::consts::{DLL_PREFIX, DLL_SUFFIX};
@@ -1177,13 +1177,8 @@ fn describe_lints(sess: &Session, lint_store: &lint::LintStore, loaded_plugins:
 
     fn sort_lints(sess: &Session, lints: Vec<(&'static Lint, bool)>) -> Vec<&'static Lint> {
         let mut lints: Vec<_> = lints.into_iter().map(|(x, _)| x).collect();
-        lints.sort_by(|x: &&Lint, y: &&Lint| {
-            match x.default_level(sess).cmp(&y.default_level(sess)) {
-                // The sort doesn't case-fold but it's doubtful we care.
-                Equal => x.name.cmp(y.name),
-                r => r,
-            }
-        });
+        // The sort doesn't case-fold but it's doubtful we care.
+        lints.sort_by_cached_key(|x: &&Lint| (x.default_level(sess), x.name));
         lints
     }
 

src/libsyntax/lib.rs

@@ -22,6 +22,7 @@
 
 #![feature(unicode)]
 #![feature(rustc_diagnostic_macros)]
+#![feature(slice_sort_by_cached_key)]
 #![feature(non_exhaustive)]
 #![feature(const_atomic_usize_new)]
 #![feature(rustc_attrs)]

src/libsyntax/parse/parser.rs

@@ -689,7 +689,7 @@ fn tokens_to_string(tokens: &[TokenType]) -> String {
                 .chain(inedible.iter().map(|x| TokenType::Token(x.clone())))
                 .chain(self.expected_tokens.iter().cloned())
                 .collect::<Vec<_>>();
-            expected.sort_by(|a, b| a.to_string().cmp(&b.to_string()));
+            expected.sort_by_cached_key(|x| x.to_string());
             expected.dedup();
             let expect = tokens_to_string(&expected[..]);
             let actual = self.this_token_to_string();