`std` uses a `Thin` trait alias which breaks mir eval

[Veykril]

https://doc.rust-lang.org/std/ptr/fn.null_mut.html is defined as:

pub const fn null_mut<T: ?Sized + Thin>() -> *mut T;

where Thin is defined as:

pub trait Thin = Pointee<Metadata = ()>;

r-a currently does not handle trait aliases correctly, as such mir eval bails out on almost all code that does Vec allocations via Vec::with_capacity because we lack the knowledge that Metadata = () in null_mut resulting in a Expected <T as Pointee>::Metadata, found () error.

[Veykril]

@HKalbasi this is the cause for the mir failures (or at least part of them)

[HKalbasi]

Yes it seems this is the reason of failure in mir eval of debug impls. For mir lowering failures the problem was in the stats, fixed by #15567