remove unnecessary to_string and String::new

compiler/rustc_builtin_macros/src/assert.rs

@@ -132,7 +132,7 @@ fn parse_assert<'a>(cx: &mut ExtCtxt<'a>, sp: Span, stream: TokenStream) -> PRes
         err.span_suggestion(
             parser.token.span,
             "try removing semicolon",
-            String::new(),
+            "",
             Applicability::MaybeIncorrect,
         );
         err.emit();
@@ -153,7 +153,7 @@ fn parse_assert<'a>(cx: &mut ExtCtxt<'a>, sp: Span, stream: TokenStream) -> PRes
             err.span_suggestion_short(
                 comma_span,
                 "try adding a comma",
-                ", ".to_string(),
+                ", ",
                 Applicability::MaybeIncorrect,
             );
             err.emit();

compiler/rustc_builtin_macros/src/derive.rs

@@ -142,7 +142,7 @@ fn report_path_args(sess: &Session, meta: &ast::MetaItem) {
     let report_error = |title, action| {
         let span = meta.span.with_lo(meta.path.span.hi());
         sess.struct_span_err(span, title)
-            .span_suggestion(span, action, String::new(), Applicability::MachineApplicable)
+            .span_suggestion(span, action, "", Applicability::MachineApplicable)
             .emit();
     };
     match meta.kind {

compiler/rustc_builtin_macros/src/test.rs

@@ -118,7 +118,7 @@ pub fn expand_test_or_bench(
         };
         err.span_label(attr_sp, "the `#[test]` macro causes a a function to be run on a test and has no effect on non-functions")
             .span_label(item.span, format!("expected a non-associated function, found {} {}", item.kind.article(), item.kind.descr()))
-            .span_suggestion(attr_sp, "replace with conditional compilation to make the item only exist when tests are being run", String::from("#[cfg(test)]"), Applicability::MaybeIncorrect)
+            .span_suggestion(attr_sp, "replace with conditional compilation to make the item only exist when tests are being run", "#[cfg(test)]", Applicability::MaybeIncorrect)
             .emit();
 
         return vec![Annotatable::Item(item)];