#[pin_project] panics with `internal error: entered unreachable code` when used inside a MBE with vis

[WaffleLapkin]

On latest nightly (1.51.0-nightly (2021-01-14 e38fb306b7f5e65cca34)) started panicing with internal error: entered unreachable code message.

MRE:

#[macro_use]
macro_rules! req_future {
    ($v:vis) => {
        #[pin_project::pin_project]
        $v struct Send
        {
            #[pin]
            inner: ()
        }
    };
}

req_future! { pub }

(play)

[Aaron1011]

This should be fixed by rust-lang/rust#81029

[taiki-e]

Fixed in nightly-2021-02-01. Thanks @Aaron1011 for the fix!