From a0933bd8ec1515167ea653f7ee788b8bbde27d51 Mon Sep 17 00:00:00 2001
From: Mike Rice <michael.p.rice@intel.com>
Date: Wed, 8 May 2019 17:15:21 +0000
Subject: [PATCH] Include corecrt.h in stddef.h and vcruntime.h in stdarg.h to
 improve MS compatibility.  This allows some applications developed with MSVC
 to compile with clang without any extra changes.

Fixes: llvm.org/PR40789

Differential Revision: https://reviews.llvm.org/D61646

llvm-svn: 360271
---
 clang/lib/Headers/stdarg.h                         |  5 +++++
 clang/lib/Headers/stddef.h                         |  6 ++++++
 clang/test/Headers/Inputs/ms-crt/corecrt.h         |  1 +
 clang/test/Headers/Inputs/ms-crt/vcruntime.h       |  1 +
 clang/test/Headers/c11.c                           |  3 ++-
 clang/test/Headers/ms-additional-includes.cpp      | 10 ++++++++++
 clang/test/Headers/ms-null-ms-header-vs-stddef.cpp |  3 ++-
 7 files changed, 27 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/Headers/Inputs/ms-crt/corecrt.h
 create mode 100644 clang/test/Headers/Inputs/ms-crt/vcruntime.h
 create mode 100644 clang/test/Headers/ms-additional-includes.cpp

diff --git a/clang/lib/Headers/stdarg.h b/clang/lib/Headers/stdarg.h
index 0bc39408c1e5..97b3c082ec8b 100644
--- a/clang/lib/Headers/stdarg.h
+++ b/clang/lib/Headers/stdarg.h
@@ -10,6 +10,11 @@
 #ifndef __STDARG_H
 #define __STDARG_H
 
+#if defined(_MSC_VER)
+/* Include otherwise unneeded header for MSVC compatibility. */
+#include <vcruntime.h>
+#endif
+
 #ifndef _VA_LIST
 typedef __builtin_va_list va_list;
 #define _VA_LIST
diff --git a/clang/lib/Headers/stddef.h b/clang/lib/Headers/stddef.h
index 15acd4427ca1..860c909eff29 100644
--- a/clang/lib/Headers/stddef.h
+++ b/clang/lib/Headers/stddef.h
@@ -18,6 +18,12 @@
 #if !__has_feature(modules)
 #define __STDDEF_H
 #endif
+
+#if defined(_MSC_VER)
+/* Include otherwise unneeded header for MSVC compatibility. */
+#include <corecrt.h>
+#endif
+
 #define __need_ptrdiff_t
 #define __need_size_t
 #define __need_wchar_t
diff --git a/clang/test/Headers/Inputs/ms-crt/corecrt.h b/clang/test/Headers/Inputs/ms-crt/corecrt.h
new file mode 100644
index 000000000000..6f70f09beec2
--- /dev/null
+++ b/clang/test/Headers/Inputs/ms-crt/corecrt.h
@@ -0,0 +1 @@
+#pragma once
diff --git a/clang/test/Headers/Inputs/ms-crt/vcruntime.h b/clang/test/Headers/Inputs/ms-crt/vcruntime.h
new file mode 100644
index 000000000000..6f70f09beec2
--- /dev/null
+++ b/clang/test/Headers/Inputs/ms-crt/vcruntime.h
@@ -0,0 +1 @@
+#pragma once
diff --git a/clang/test/Headers/c11.c b/clang/test/Headers/c11.c
index 6594823c2733..e5e8ae425f9e 100644
--- a/clang/test/Headers/c11.c
+++ b/clang/test/Headers/c11.c
@@ -2,7 +2,8 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c11 %s
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c11 -fmodules -fmodules-cache-path=%t %s -D__STDC_WANT_LIB_EXT1__=1
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c11 -ffreestanding %s
-// RUN: %clang_cc1 -fsyntax-only -verify -std=c11 -triple i686-pc-win32 -fms-compatibility-version=17.00 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c11 -triple i686-pc-win32 \
+// RUN:  -fms-compatibility-version=17.00 -isystem %S/Inputs/ms-crt %s
 
 noreturn int f(); // expected-error 1+{{}}
 
diff --git a/clang/test/Headers/ms-additional-includes.cpp b/clang/test/Headers/ms-additional-includes.cpp
new file mode 100644
index 000000000000..3c6506a5a512
--- /dev/null
+++ b/clang/test/Headers/ms-additional-includes.cpp
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -fsyntax-only --show-includes -triple i686-pc-win32 \
+// RUN:  -isystem %S/Inputs/ms-crt -fms-compatibility-version=17.00 %s \
+// RUN:  | FileCheck %s
+
+#include <stddef.h>
+// CHECK: including file:{{.*}}stddef.h
+// CHECK: including file:{{.*}}corecrt.h
+#include <stdarg.h>
+// CHECK: including file:{{.*}}stdarg.h
+// CHECK: including file:{{.*}}vcruntime.h
diff --git a/clang/test/Headers/ms-null-ms-header-vs-stddef.cpp b/clang/test/Headers/ms-null-ms-header-vs-stddef.cpp
index f39a0cafaa0d..bd81b6287bf4 100644
--- a/clang/test/Headers/ms-null-ms-header-vs-stddef.cpp
+++ b/clang/test/Headers/ms-null-ms-header-vs-stddef.cpp
@@ -1,4 +1,5 @@
-// RUN: %clang_cc1 -fsyntax-only -triple i686-pc-win32 -fms-compatibility -fms-compatibility-version=17.00 %s
+// RUN: %clang_cc1 -fsyntax-only -triple i686-pc-win32 -fms-compatibility \
+// RUN:  -isystem %S/Inputs/ms-crt -fms-compatibility-version=17.00 %s
 // RUN: %clang_cc1 -fsyntax-only -triple i386-mingw32 %s
 
 // Something in MSVC's headers (pulled in e.g. by <crtdefs.h>) defines __null