Fix #15453

Author: Jakub Wieczorek

src/librustc/middle/check_match.rs

@@ -563,6 +563,7 @@ pub fn constructor_arity(cx: &MatchCheckCtxt, ctor: &Constructor, ty: ty::t) ->
         ty::ty_rptr(_, ty::mt { ty: ty, .. }) => match ty::get(ty).sty {
             ty::ty_vec(_, None) => match *ctor {
                 Slice(length) => length,
+                ConstantValue(_) => 0u,
                 _ => unreachable!()
             },
             ty::ty_str => 0u,

src/test/run-pass/byte-literals.rs

@@ -46,6 +46,13 @@ pub fn main() {
         _ => fail!(),
     }
 
+    let buf = vec!(97u8, 98, 99, 100);
+    assert_eq!(match buf.slice(0, 3) {
+         b"def" => 1u,
+         b"abc" => 2u,
+         _ => 3u
+    }, 2);
+
     assert_eq!(BAZ, &[97u8, 92u8, 110u8]);
     assert_eq!(br"a\n", &[97u8, 92u8, 110u8]);
     assert_eq!(br"a\n", b"a\\n");