Incorrect error message when using associated type in const expression

[RalfJung]

trait VecN {
    const DIM: usize;
}
trait Mat {
    type Row: VecN;
}

fn m<M: Mat>() {
    let a = [3; M::Row::DIM]; //~ ERROR associated type `Row` not found for `M`
}
fn main() {
}

The associated type actually exists. So I started at this a while, wondering whether I just stopped knowing how to read...

(Originally reported at #34344 (comment).)

[nwin]

Duplicate of #44168.

[shepmaster]

Closing as duplicate