Use sort_by_key rather than sort_by

Author: AnthonyMikh

src/librustc_errors/emitter.rs

@@ -954,9 +954,9 @@ impl EmitterWriter {
         //   | |  |
         //   | |  something about `foo`
         //   | something about `fn foo()`
-        annotations_position.sort_by(|a, b| {
+        annotations_position.sort_by_key(|x| {
             // Decreasing order. When `a` and `b` are the same length, prefer `Primary`.
-            (a.1.len(), !a.1.is_primary).cmp(&(b.1.len(), !b.1.is_primary)).reverse()
+            (Reverse(a.1.len()), a.1.is_primary)
         });
 
         // Write the underlines.