Spurious unused field warning when matching variants under a `Self` scope

[jakubadamw]

This code should compile without warnings:

enum Enum {
    Variant { field: usize }
}
impl Enum {
    fn read_field(self) -> usize {
        match self {
            // Enum::Variant { field } => field
            Self::Variant { field } => field
        }
    }
}
fn main() {
    let e = Enum::Variant { field: 42 };
    println!("{}", e.read_field());
}

However, it produces the following one:

warning: field is never used: `field`
 --> src/main.rs:2:15
  |
2 |     Variant { field: usize }
  |               ^^^^^^^^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

If we switch the pattern within match to the one that's commented out, the warning is gone.