Bad generic inference on very recent nightly

[dlubarov]

We noticed a build error in Plonky2 on the nightly build 2022-11-27. The same code was building last week, on a slightly older nightly.

Here's a minimal reproducible example (Playground):

#![feature(generic_const_exprs)]

trait Table<const D: usize>: Sync {
    const COLUMNS: usize;
}

struct Table1<const D: usize>;
impl<const D: usize> Table<D> for Table1<D> {
    const COLUMNS: usize = 123;
}

struct Table2<const D: usize>;
impl<const D: usize> Table<D> for Table2<D> {
    const COLUMNS: usize = 456;
}

fn process_table<T: Table<D>, const D: usize>(table: T)
where
    [(); T::COLUMNS]:,
{
}

fn process_all_tables<const D: usize>()
where
    [(); Table1::<D>::COLUMNS]:,
    [(); Table2::<D>::COLUMNS]:,
{
    process_table(Table1::<D>);
    process_table(Table2::<D>);
}

Nightly 2022-11-27 gives this error:

error[[E0308]](https://doc.rust-lang.org/nightly/error-index.html#E0308): mismatched types
  --> src/lib.rs:28:19
   |
28 |     process_table(Table1::<D>);
   |     ------------- ^^^^^^^^^^^ expected struct `Table2`, found struct `Table1`
   |     |
   |     arguments to this function are incorrect
   |
   = note: expected struct `Table2<D>`
              found struct `Table1<D>`

It seems to be sensitive to the order of the where clauses, [(); Table1::<D>::COLUMNS]: and [(); Table2::<D>::COLUMNS]:. I.e. for a process_table call, it seems to infer that T is whichever Table appeared last in the where list.

[mucinoab]

@compiler-errors Please remove the "E-needs-bisection" (also, how can I do that?)

searched nightlies: from nightly-2022-11-25 to nightly-2022-11-29
regressed nightly: nightly-2022-11-27
searched commit range: 8681d4c...80a9646
regressed commit: aff003b

bisected with cargo-bisect-rustc v0.6.4

Host triple: x86_64-unknown-linux-gnu

[compiler-errors]

thanks @mucinoab

cc @BoxyUwU @JulianKnodt