borrow-vec associated with bad sty: &ty_err

[mahkoh]

fn main() {
    extern {
        fn f(v: *mut i8);
    }
    // let mut buf = [0i8];
    // let mut buf = [0u8];
    // let mut buf = [0u];
    let mut buf = [0];
    unsafe { f(buf.as_mut_ptr() as *mut _); }
}

test.rs:6:16: 6:19 error: internal compiler error: borrow-vec associated with bad sty: &ty_err
test.rs:6     unsafe { f(buf.as_mut_ptr() as *mut _); }

Worked some time ago. All other versions work.

[huonw]

Dupe of #7813. Now that integer fallback is removed, the element type of the array is unknown, causing the method call to ice (previously it was inferring to int, so the cast was converting *mut int to *mut i8).