remove unnecessary to_string and String::new

compiler/rustc_expand/src/base.rs

@@ -1194,7 +1194,7 @@ pub fn expr_to_spanned_string<'a>(
                 err.span_suggestion(
                     expr.span.shrink_to_lo(),
                     "consider removing the leading `b`",
-                    String::new(),
+                    "",
                     Applicability::MaybeIncorrect,
                 );
                 Some((err, true))

compiler/rustc_expand/src/expand.rs

@@ -945,7 +945,7 @@ pub fn ensure_complete_parse<'a>(
                 err.span_suggestion(
                     semi_span,
                     "you might be missing a semicolon here",
-                    ";".to_owned(),
+                    ";",
                     Applicability::MaybeIncorrect,
                 );
             }

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -102,7 +102,7 @@ fn emit_frag_parse_err(
                 e.span_suggestion_verbose(
                     site_span.shrink_to_hi(),
                     "add `;` to interpret the expansion as a statement",
-                    ";".to_string(),
+                    ";",
                     Applicability::MaybeIncorrect,
                 );
             }
@@ -357,7 +357,7 @@ fn expand_macro<'cx>(
                     err.span_suggestion_short(
                         comma_span,
                         "missing comma here",
-                        ", ".to_string(),
+                        ", ",
                         Applicability::MachineApplicable,
                     );
                 }

compiler/rustc_expand/src/mbe/metavar_expr.rs

@@ -52,7 +52,7 @@ impl MetaVarExpr {
                 err.span_suggestion(
                     ident.span,
                     "supported expressions are count, ignore, index and length",
-                    String::new(),
+                    "",
                     Applicability::MachineApplicable,
                 );
                 return Err(err);
@@ -142,7 +142,7 @@ fn parse_ident<'sess>(
         err.span_suggestion(
             token.span,
             &format!("try removing `{}`", &token_str),
-            String::new(),
+            "",
             Applicability::MaybeIncorrect,
         );
         return Err(err);