`await` is not treated as a plain token in a macro

[kuretchi]

macro_rules! m {
    ($($t:tt)*) => {};
}
m! { async try dyn await }

Compiling this code on the 2018 edition causes an following error:

error[E0721]: `await` is a keyword in the 2018 edition
 --> src/main.rs:4:20
  |
4 | m! { async try dyn await }
  |                    ^^^^^ help: you can use a raw identifier to stay compatible: `r#await`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0721`.

However, as with other keywords, this await keyword should be ignored through ($($t:tt)*) => {};.

Playground

[varkor]

This is essentially due to #54411.

The problem is that await isn't a true keyword and has been given a custom error message (triggering eagerly), which doesn't have the same handling as normal keyword use errors. It seems simplest to leave this unaddressed until the await syntax has been chosen and we can use await as a true keyword.

[dtolnay]

Fixed in 1.36.0.