use str-literal instead of char-literal before converting to String since str to String conversion is cheaper.

See rust-lang#73462

Author: matthiaskrgr

src/librustc_parse/parser/item.rs

@@ -1403,7 +1403,7 @@ impl<'a> Parser<'a> {
             };
             err.multipart_suggestion(
                 "change the delimiters to curly braces",
-                vec![(open, "{".to_string()), (close, '}'.to_string())],
+                vec![(open, "{".to_string()), (close, "}".to_string())],
                 Applicability::MaybeIncorrect,
             );
         } else {
@@ -1417,7 +1417,7 @@ impl<'a> Parser<'a> {
         err.span_suggestion(
             span.shrink_to_hi(),
             "add a semicolon",
-            ';'.to_string(),
+            ";".to_string(),
             Applicability::MaybeIncorrect,
         );
         err.emit();

src/librustc_typeck/check/method/suggest.rs

@@ -468,8 +468,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                         item_name,
                                     ),
                                     vec![
-                                        (expr_span.shrink_to_lo(), '('.to_string()),
-                                        (expr_span.shrink_to_hi(), ')'.to_string()),
+                                        (expr_span.shrink_to_lo(), "(".to_string()),
+                                        (expr_span.shrink_to_hi(), ")".to_string()),
                                     ],
                                     Applicability::MachineApplicable,
                                 );

src/librustc_typeck/collect.rs

@@ -464,7 +464,7 @@ fn get_new_lifetime_name<'tcx>(
 
     let a_to_z_repeat_n = |n| {
         (b'a'..=b'z').map(move |c| {
-            let mut s = '\''.to_string();
+            let mut s = "'".to_string();
             s.extend(std::iter::repeat(char::from(c)).take(n));
             s
         })