Fix incorrect non-exhaustive matching for fixed length vecs

[stepancheg]

Code like this is fixed now:

fn foo(p: [u8, ..4]) {
    match p {
        [a, b, c, d] => {}
    };
}

Invalid constructors are not reported as errors yet:

fn foo(p: [u8, ..4]) {
    match p {
        [_, _, _] => {} // this should be error
        [_, _, _, _, _, .._] => {} // and this
        _ => {}
    }
}

Issue #8311 is partially fixed: fixed-length vectors in let statement are not yet allowed.

[huonw]

This looks cool! Does it fix it for let too? I.e. let [a,b,c] = length_three().

[stepancheg]

@huonw no, it is the same:

tmp.rs:4:8: 4:17 error: refutable pattern in local binding
tmp.rs:4     let [a, b, c] = length_three();
                 ^~~~~~~~~
error: aborting due to previous error

It is a separate issue.

[bstrie]

Wow, very cool! But if this commit doesn't also fix this for let patterns, then please revise your commit message to remove the "Fixes" reference to #8311, because otherwise Github will close that issue automatically when the commit hits master.

[stepancheg]

@bstrie updated commit comment.