Strange error message on empty asm! macro

[phil-opp]

The following code produces a strange error:

#![feature(asm)]

fn main() { 
   unsafe { asm!() }
}

The error is:

error: expected expression, found `<eof>`

Playpen link

The error does not contain any file or line information, so it's pretty hard to find the offending line. The error also occurs on stable, where inline assembly isn't even allowed.

[asdfopiweut]

It's not about inline assembly imo:

macro_rules! emit_bug {
// if nothing on input, then return what?
    () => (); // () => (()); <-- This works
}

fn main() {
   emit_bug!() // no semicolon here
}

[phil-opp]

@asdfopiweut I can reproduce it on my machine and on playpen. The same error: expected expression, found <eof>. So I think this issue should also get A-macros.

cc @sanxiyn

[Mark-Simulacrum]

This is #30128, closing in favor of that.