Suggest space separated format str literal

src/libsyntax_ext/format.rs

@@ -728,7 +728,7 @@ pub fn expand_preparsed_format_args(ecx: &mut ExtCtxt,
         Err(mut err) => {
             let sugg_fmt = match args.len() {
                 0 => "{}".to_string(),
-                _ => format!("{}{{}}", "{}, ".repeat(args.len())),
+                _ => format!("{}{{}}", "{} ".repeat(args.len())),
 
             };
             err.span_suggestion(

src/test/ui/macros/bad_hello.stderr

@@ -15,8 +15,8 @@ LL |     println!(3, 4);
    |              ^
 help: you might be missing a string literal to format with
    |
-LL |     println!("{}, {}", 3, 4);
-   |              ^^^^^^^^^
+LL |     println!("{} {}", 3, 4);
+   |              ^^^^^^^^
 
 error: aborting due to 2 previous errors