From 86b10671dbb7edf4090cb04476b4da205fd892b2 Mon Sep 17 00:00:00 2001
From: Without Boats <woboats@gmail.com>
Date: Sun, 23 Apr 2017 22:00:09 -0700
Subject: [PATCH] Associated consts are not object safe.

---
 src/librustc/traits/object_safety.rs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/librustc/traits/object_safety.rs b/src/librustc/traits/object_safety.rs
index d190635bec3..f51711d0310 100644
--- a/src/librustc/traits/object_safety.rs
+++ b/src/librustc/traits/object_safety.rs
@@ -37,6 +37,9 @@ pub enum ObjectSafetyViolation {
 
     /// Method has something illegal
     Method(ast::Name, MethodViolationCode),
+
+    /// Associated const
+    AssociatedConst(ast::Name),
 }
 
 impl ObjectSafetyViolation {
@@ -54,6 +57,8 @@ impl ObjectSafetyViolation {
                          in its arguments or return type", name).into(),
             ObjectSafetyViolation::Method(name, MethodViolationCode::Generic) =>
                 format!("method `{}` has generic type parameters", name).into(),
+            ObjectSafetyViolation::AssociatedConst(name) =>
+                format!("the trait cannot contain associated consts, such as `{}`", name),
         }
     }
 }
@@ -141,6 +146,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             violations.push(ObjectSafetyViolation::SupertraitSelf);
         }
 
+        violations.extend(self.associated_items(trait_def_id)
+            .filter(|item| item.kind == ty::AssociatedKind::Const)
+            .map(|item| ObjectSafetyViolation::AssociatedConst(item.name)));
+
         debug!("object_safety_violations_for_trait(trait_def_id={:?}) = {:?}",
                trait_def_id,
                violations);