From e574e0eda098be1e877be7b6f92e77f82ff8fc84 Mon Sep 17 00:00:00 2001
From: Luke Wagner <luke@mozilla.com>
Date: Thu, 2 Jun 2016 14:38:02 -0500
Subject: [PATCH] Bug 1277377 - prevent unsafe C-style cast in Vector (r=waldo)

MozReview-Commit-ID: L0bTDSBHOeY
---
 mfbt/Vector.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mfbt/Vector.h b/mfbt/Vector.h
index f31aeee731a6..23a299f3b21f 100644
--- a/mfbt/Vector.h
+++ b/mfbt/Vector.h
@@ -163,7 +163,12 @@ struct VectorImpl<T, N, AP, true>
   MOZ_NONNULL(1)
   static inline void new_(T* aDst, Args&&... aArgs)
   {
-    *aDst = T(Forward<Args>(aArgs)...);
+    // Explicitly construct a local object instead of using a temporary since
+    // T(args...) will be treated like a C-style cast in the unary case and
+    // allow unsafe conversions. Both forms should be equivalent to an
+    // optimizing compiler.
+    T temp(Forward<Args>(aArgs)...);
+    *aDst = temp;
   }
 
   static inline void destroy(T*, T*) {}