Format empty dyn without trailing space

[dtolnay]

macro_rules! token {
    ($t:tt) => {};
}

fn main() {
    token!(dyn);
}

As of current master, in 2018 edition mode rustfmt applies the following diff:

-     token!(dyn);
+     token!(dyn );

I would prefer for there not to be a trailing space inserted. @topecongiro -- I believe this should fall under #3333.

Affects the Token! macro in Syn.

[KamWithK]

I would like to fix this.
I've had a look at #3333 however can't find token!(dyn) in the diffs

[topecongiro]

@KamWithK Thanks! IIRC all you need to do is to flip the order of these two function calls:

rustfmt/src/macros.rs

Lines 306 to 309 in 3adfb08

	if let Some(arg) = parse_macro_arg(&mut parser) {
	arg_vec.push(arg);
	} else if let Some(arg) = check_keyword(&mut parser) {
	arg_vec.push(arg);

When you create a PR, please do not forget to add a test :). Also, note that this issue is reproducible only when we are using edition 2018.

[KamWithK]

Hey, just wanted to let you know that I won't be able to work on this as a result of my lack of time right now