address review feedback (sort_by_key is so much cleaner here than sort_by!).

pnkfelix · pnkfelix · commit 779792ff384c · 2018-07-31T23:00:01.000+02:00
diff --git a/src/librustc_mir/borrow_check/mod.rs b/src/librustc_mir/borrow_check/mod.rs
@@ -331,9 +331,7 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
     }
 
     if mbcx.errors_buffer.len() > 0 {
-        mbcx.errors_buffer.sort_by(|diag1, diag2| {
-            diag1.span.primary_span().cmp(&diag2.span.primary_span())
-        });
+        mbcx.errors_buffer.sort_by_key(|diag| diag.span.primary_span());
 
         if tcx.migrate_borrowck() {
             match tcx.borrowck(def_id).signalled_any_error {

Original file line number	Diff line number	Diff line change
`@@ -331,9 +331,7 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(`
`331`	`331`	`}`
`332`	`332`
`333`	`333`	`if mbcx.errors_buffer.len() > 0 {`
`334`		`- mbcx.errors_buffer.sort_by(\|diag1, diag2\| {`
`335`		`- diag1.span.primary_span().cmp(&diag2.span.primary_span())`
`336`		`- });`
	`334`	`+ mbcx.errors_buffer.sort_by_key(\|diag\| diag.span.primary_span());`
`337`	`335`
`338`	`336`	`if tcx.migrate_borrowck() {`
`339`	`337`	`match tcx.borrowck(def_id).signalled_any_error {`