From 27fab5cd94531dde1ffd71cd80a5459925d4096c Mon Sep 17 00:00:00 2001
From: Orvid King <blah38621@gmail.com>
Date: Wed, 12 Aug 2015 12:45:01 -0700
Subject: [PATCH] Explicitly exclude StringPiece from FormatValue in trace.h

Summary: For some reason, MSVC seems to have decided that StringPiece is able to match the constraint, and thus complains that multiple template instantiations could be valid.
This explicitly checks that `Val` is not `StringPiece`, which is good enough to solve the problem.
Closes https://github.com/facebook/hhvm/pull/5801

Reviewed By: @mxw

Differential Revision: D2282477
---
 hphp/util/trace.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/hphp/util/trace.h b/hphp/util/trace.h
index 4b45f99448b..16448a69823 100644
--- a/hphp/util/trace.h
+++ b/hphp/util/trace.h
@@ -445,7 +445,11 @@ namespace folly {
 template<typename Val>
 struct FormatValue<Val,
                    typename std::enable_if<
-                     HPHP::has_toString<Val, std::string() const>::value,
+                     HPHP::has_toString<Val, std::string() const>::value &&
+                     // This is here because MSVC decides that StringPiece matches
+                     // both this overload as well as the FormatValue overload for
+                     // string-y types in folly itself.
+                     !std::is_same<Val, StringPiece>::value,
                      void
                    >::type> {
   explicit FormatValue(const Val& val) : m_val(val) {}
-- 
2.11.4.GIT