v.view(..) method has different borrow-check constraints than vec::slice(v, ..)

[pnkfelix]

This is spawned off from #3888.

If you swap in the first line below instead of the second, the example will compile.

fn vec_peek<T>(v: &'r [T]) -> &'r [T] {
    // let tail = vec::slice(v, 1, v.len());
    let tail = v.view(1, v.len());
    tail
}

Without the fix described above, you get the following compilation failure (rustc from commit c202430):

% rustc --lib /tmp/foo3.rs
/tmp/foo3.rs:3:15: 3:16 error: illegal borrow: borrowed value does not live long enough
/tmp/foo3.rs:3     let tail = v.view(1, v.len());
                              ^
/tmp/foo3.rs:1:38: 5:1 note: borrowed pointer must be valid for the lifetime &'r  as defined on the block at 1:38...
/tmp/foo3.rs:1 fn vec_peek<T>(v: &'r [T]) -> &'r [T] {
/tmp/foo3.rs:2     // let tail = vec::slice(v, 1, v.len());
/tmp/foo3.rs:3     let tail = v.view(1, v.len());
/tmp/foo3.rs:4     tail
/tmp/foo3.rs:5 }
/tmp/foo3.rs:1:0: 5:1 note: ...but borrowed value is only valid for the function body at 1:0
/tmp/foo3.rs:1 fn vec_peek<T>(v: &'r [T]) -> &'r [T] {
/tmp/foo3.rs:2     // let tail = vec::slice(v, 1, v.len());
/tmp/foo3.rs:3     let tail = v.view(1, v.len());
/tmp/foo3.rs:4     tail
/tmp/foo3.rs:5 }
error: aborting due to previous error

[lifthrasiir]

Possibly related to #5550?