Infer type in irrefutable slice patterns with fixed length as array
Fixes https://github.com/rust-lang/rust/issues/76342
In irrefutable slice patterns with a fixed length, we can infer the type as an array type. We now choose to prefer some implementations over others, e.g. in:
```
struct Zeroes;
const ARR: [usize; 2] = [0; 2];
const ARR2: [usize; 2] = [2; 2];
impl Into<&'static [usize; 2]> for Zeroes {
fn into(self) -> &'static [usize; 2] {
&ARR
}
}
impl Into<&'static [usize]> for Zeroes {
fn into(self) -> &'static [usize] {
&ARR2
}
}
fn main() {
let &[a, b] = Zeroes.into();
}
```
We now prefer the impl candidate `impl Into<&'static [usize; 2]> for Zeroes`, it's not entirely clear to me that this is correct, but given that the slice impl would require a type annotation anyway, this doesn't seem unreasonable.
r? `@lcnr`
fcf3006e01