From 4fb789b86eb4d9f50c1ae6477126cd84025ff566 Mon Sep 17 00:00:00 2001
From: Seo Sanghyeon <sanxiyn@gmail.com>
Date: Sat, 26 Sep 2015 11:52:34 +0900
Subject: [PATCH] Provide the context for error in constant evaluation of enum
 discriminant

---
 src/librustc_typeck/collect.rs           |  9 ++++++---
 src/test/compile-fail/const-eval-span.rs | 24 ++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 3 deletions(-)
 create mode 100644 src/test/compile-fail/const-eval-span.rs

diff --git a/src/librustc_typeck/collect.rs b/src/librustc_typeck/collect.rs
index 39805bfc8a3e2..7a70bc73b7338 100644
--- a/src/librustc_typeck/collect.rs
+++ b/src/librustc_typeck/collect.rs
@@ -1173,9 +1173,12 @@ fn convert_enum_def<'tcx>(tcx: &ty::ctxt<'tcx>,
                 None
             },
             Err(err) => {
-              span_err!(tcx.sess, err.span, E0080,
-                        "constant evaluation error: {}",
-                        err.description());
+                span_err!(tcx.sess, err.span, E0080,
+                          "constant evaluation error: {}",
+                          err.description());
+                if !e.span.contains(err.span) {
+                    tcx.sess.span_note(e.span, "for enum discriminant here");
+                }
                 None
             }
         }
diff --git a/src/test/compile-fail/const-eval-span.rs b/src/test/compile-fail/const-eval-span.rs
new file mode 100644
index 0000000000000..8e9209916f35b
--- /dev/null
+++ b/src/test/compile-fail/const-eval-span.rs
@@ -0,0 +1,24 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Check that error in constant evaluation of enum discriminant
+// provides the context for what caused the evaluation.
+
+struct S(i32);
+
+const CONSTANT: S = S(0);
+//~^ ERROR: constant evaluation error: unsupported constant expr
+
+enum E {
+    V = CONSTANT,
+    //~^ NOTE: for enum discriminant here
+}
+
+fn main() {}