better error reporting

Author: Oliver Schneider

src/librustc_trans/trans/consts.rs

@@ -612,9 +612,19 @@ fn const_expr_unadjusted<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
           ast::ExprIndex(ref base, ref index) => {
               match const_eval::eval_const_expr_partial(cx.tcx(), &e, None) {
                   Ok(val) => const_val_for_idx(cx, val, param_substs, ety),
-                  Err(NonConstPath) => {
+                  Err(const_eval::ConstEvalErr {
+                      kind: const_eval::ErrKind::NonConstPath, ..
+                  }) | Err(const_eval::ConstEvalErr {
+                      kind: const_eval::ErrKind::MiscCatchAll, ..
+                  }) => {
               let (bv, bt) = const_expr(cx, &**base, param_substs);
-              let iv = try!(const_eval::eval_const_index(cx.tcx(), &**index));
+              let iv = match const_eval::eval_const_index(cx.tcx(), &**index) {
+                  Ok(idx) => idx,
+                  Err(err) => {
+                      cx.sess().span_err(err.span, &*err.description());
+                      cx.sess().span_fatal(index.span,"constant evaluation of index failed");
+                  },
+              };
               let (arr, len) = match bt.sty {
                   ty::ty_vec(_, Some(u)) => (bv, C_uint(cx, u)),
                   ty::ty_vec(_, None) | ty::ty_str => {
@@ -659,10 +669,10 @@ fn const_expr_unadjusted<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                   const_get_elt(cx, arr, &[iv as c_uint])
               }
                   },
-                  Err(err) => cx.sess().span_fatal(
-                      e.span,
-                      &format!("constant indexing failed: {}", err.description()),
-                  ),
+                  Err(err) => {
+                      cx.sess().span_err(err.span, &*err.description());
+                      cx.sess().span_fatal(e.span,"constant indexing failed");
+                  },
               }
           }
           ast::ExprCast(ref base, _) => {