Matching fixed-size vectors requires handling vectors of arbitrary size

I'm trying to use pattern matching with fixed-size vectors, like this:

fn main() {
    match [3, 5] {
        [a, b] => println("ok")
    };
}

However, this doesn't compile (I'm using 0.6 on Windows):

error: non-exhaustive patterns: vectors of length 0 not covered

After adding a wildcard the program compiles...

fn main() {
    match [3, 5] {
        [a, b] => println("ok"),
        _ => ()
    };
}

... which I think it shouldn't, since that last pattern is (or should be) unreachable. When replacing the fixed-size vector with a tuple, it certainly is:

fn main() {
    match (3, 5) {
        (a, b) => println("ok"),
        _ => ()
    };
}

error: unreachable pattern

[huonw]

Hi, it looks like #7784 was accidentally filed too; I'm closing this one as a dup because that issue uses the appropriate jargon, which helps when searching.