"Cannot infer appropriate lifetime" points at associated const of type Option<!>

[RalfJung]

I have no idea what is going on in this piece of code:

#![feature(never_type)]

use std::marker::PhantomData;

pub trait Machine<'a, 'mir, 'tcx>: Sized {
    type MemoryKinds: ::std::fmt::Debug + Copy + Eq;
    const MUT_STATIC_KIND: Option<Self::MemoryKinds>;
}

pub struct CompileTimeEvaluator<'a, 'mir, 'tcx: 'a+'mir> {
    pub _data: PhantomData<(&'a (), &'mir (), &'tcx ())>,
}

impl<'a, 'mir, 'tcx: 'a + 'mir> Machine<'a, 'mir, 'tcx>
    for CompileTimeEvaluator<'a, 'mir, 'tcx>
{
    type MemoryKinds = !;

    const MUT_STATIC_KIND: Option<!> = None;
}

when it fails to compile saying

error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'tcx` due to conflicting requirements
  --> src/lib.rs:19:5
   |
19 |     const MUT_STATIC_KIND: Option<!> = None;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: first, the lifetime cannot outlive the lifetime 'tcx as defined on the impl at 14:16...
  --> src/lib.rs:14:16
   |
14 | impl<'a, 'mir, 'tcx: 'a + 'mir> Machine<'a, 'mir, 'tcx>
   |                ^^^^
note: ...but the lifetime must also be valid for the lifetime 'a as defined on the impl at 14:6...
  --> src/lib.rs:14:6
   |
14 | impl<'a, 'mir, 'tcx: 'a + 'mir> Machine<'a, 'mir, 'tcx>
   |      ^^
   = note: ...so that the types are compatible:
           expected Machine<'a, 'mir, 'tcx>
              found Machine<'_, '_, '_>

error: aborting due to previous error

I would expect the code to be accepted. How can something of type Option<!> have problems inferring a lifetime?!? The error is entirely not helpful.

Curiously, if I remove the 'a + 'mir bound on 'tcx in the impl, this compiles. Removing a bound that's already implied by the type itself should not make a difference, right?

[estebank]

Also happens under nll.

[Spoonbender]

Triage: resolved

The code compiles on nightly 1.16.0-nightly

I think we can close this one