semicolon-if-nothing-returned: macro: type cannot be inferred

[matthiaskrgr]

#![feature(custom_mir, core_intrinsics)]

extern crate core;
use core::intrinsics::mir::*;


#[repr(u8)]
enum Bool {
    False = 0,
    True = 1,
}


// EMIT_MIR enums.set_discr_repr.built.after.mir
#[custom_mir(dialect = "runtime", phase = "initial")]
fn set_discr_repr(b: &mut Bool) {
    mir!({
        SetDiscriminant(*b, 0);
        Return()
    })
}

fn main() {

}

clippy::semicolon-if-nothing-returned warns here:

warning: consider adding a `;` to the last statement for consistent formatting
  --> ./tests/mir-opt/building/custom/enums.rs:17:5
   |
17 | /     mir!({
18 | |         SetDiscriminant(*b, 0);
19 | |         Return()
20 | |     })
   | |______^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#semicolon_if_nothing_returned
   = note: requested on the command line with `-W clippy::semicolon-if-nothing-returned`
help: add a `;` here
   |
17 ~     mir!({
18 +         SetDiscriminant(*b, 0);
19 +         Return()
20 +     });

but if I add a semicolon, rustc find it cannot infer the type which it needs to make sure the macro does in fact return ()

error[E0282]: type annotations needed
  --> ./tests/mir-opt/building/custom/enums.rs:17:5
   |
17 | /     mir!({
18 | |         SetDiscriminant(*b, 0);
19 | |         Return()
20 | |     });
   | |______^ cannot infer type
   |
   = note: this error originates in the macro `mir` (in Nightly builds, run with -Z macro-backtrace for more info)