need to get the Expr_ out of the P

Author: Oliver Schneider

src/librustc_trans/trans/consts.rs

@@ -614,7 +614,7 @@ fn const_expr_unadjusted<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                   Ok(val) => const_val_for_idx(cx, val, param_substs, ety),
                   Err(NonConstPath) => {
               let (bv, bt) = const_expr(cx, &**base, param_substs);
-              let iv = try!(const_eval::eval_const_index(cx.tcx(), index));
+              let iv = try!(const_eval::eval_const_index(cx.tcx(), &**index));
               let (arr, len) = match bt.sty {
                   ty::ty_vec(_, Some(u)) => (bv, C_uint(cx, u)),
                   ty::ty_vec(_, None) | ty::ty_str => {