Binary string literals are of type &[u8] instead of &[u8, ..n]

[ftxqxd]

Intuitively, I would expect b"abc" to behave identically to &[97, 98, 99], but it does not: b"abc" is of type &[u8] instead of &[u8, ..3] like &[97, 98, 99] is. Changing this to &[u8, ..n] would provide more flexibility, as &[u8, ..n] can always be converted to &[u8], but not vice-versa.

Presumably this was either intentional or simply forgotten during the slice-related DST changes.

[nham]

Just bumping this to note that this still seems to be the case:

<anon>:2:23: 2:29 error: mismatched types:
 expected `&[u8; 3]`,
    found `&'static [u8]`
(expected array of 3 elements,
    found slice) [E0308]
<anon>:2     let x: &[u8; 3] = b"abc";
                               ^~~~~~

[ftxqxd]

This is done. (See #18465.)