From 6b5c08ab347ee1853eb7774443f28a82203f3ad0 Mon Sep 17 00:00:00 2001
From: Peter Collingbourne <peter@pcc.me.uk>
Date: Fri, 26 Jan 2018 01:19:23 +0000
Subject: [PATCH] libcxx: Move #include_next <math.h> out of header guard in
 wrapper header.

Code on Windows expects to be able to do:

 #define _USE_MATH_DEFINES
 #include <math.h>

and receive the definitions of mathematical constants, even if <math.h>
has previously been included. To support this scenario, re-include
<math.h> every time the wrapper header is included.

Differential Revision: https://reviews.llvm.org/D42403

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@323490 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/math.h                                | 12 ++++++++--
 test/libcxx/depr/depr.c.headers/math_h.sh.cpp | 23 +++++++++++++++++++
 2 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 test/libcxx/depr/depr.c.headers/math_h.sh.cpp

diff --git a/include/math.h b/include/math.h
index 8c30ba85d..147677235 100644
--- a/include/math.h
+++ b/include/math.h
@@ -8,6 +8,16 @@
 //
 //===----------------------------------------------------------------------===//
 
+// This include lives outside the header guard in order to support an MSVC
+// extension which allows users to do:
+//
+// #define _USE_MATH_DEFINES
+// #include <math.h>
+//
+// and receive the definitions of mathematical constants, even if <math.h>
+// has previously been included.
+#include_next <math.h>
+
 #ifndef _LIBCPP_MATH_H
 #define _LIBCPP_MATH_H
 
@@ -298,8 +308,6 @@ long double    truncl(long double x);
 #pragma GCC system_header
 #endif
 
-#include_next <math.h>
-
 #ifdef __cplusplus
 
 // We support including .h headers inside 'extern "C"' contexts, so switch
diff --git a/test/libcxx/depr/depr.c.headers/math_h.sh.cpp b/test/libcxx/depr/depr.c.headers/math_h.sh.cpp
new file mode 100644
index 000000000..8048865c3
--- /dev/null
+++ b/test/libcxx/depr/depr.c.headers/math_h.sh.cpp
@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// RUN: %compile -fsyntax-only
+
+#ifdef _MSC_VER
+
+#include <math.h>
+
+#define _USE_MATH_DEFINES
+#include <math.h>
+
+#ifndef M_PI
+#error M_PI not defined
+#endif
+
+#endif