Match matches in strange dependence of surrounding patterns

[nwin]

The following code

fn main() {
    let a = vec![16u8];
    match (a.as_slice(), "a") {
        ([8], "a")
        |([8, _], "a") => {},
        ([16], "a")
        |([16, _], "a") => { println!("matched") },
        // (_, _) => fail!(), // Fails if this line is used
        _ => fail!() // prints matched if this line is used

    }
}

fails, if the comment is swapped between the two last lines.

But (_, _) only matches when I use |([8, _], "a") in the first pattern and if I use a [16] instead of [8] as a value for a. I don't think this behaves as intended.

[alexcrichton]

cc @jakub-

[ghost]

This is a dupe of #16648 and fixed in #16883.

[alexcrichton]

Thanks @jakub-!