Fix PR39749 - Headers containing just #error harm __has_include.

This patch changes <experimental/foo> to use #warning instead of
is harmful to common feature detection idioms.

We should also consider only emitting the warning when __DEPRECATED is
defined, like we do in the <ext/foo> headers. Users may want to specify
"-Werror=-W#warnings" while still ignoring the libc++ warnings.

llvm-svn: 350485

8 files changed, 99 insertions, 19 deletions

diff --git a/libcxx/include/experimental/any b/libcxx/include/experimental/any
index 1dcdd0f25ec..d9c95342589 100644
--- a/libcxx/include/experimental/any
+++ b/libcxx/include/experimental/any
@@ -1,11 +1,21 @@
 // -*- C++ -*-
-//===------------------------------ any -----------------------------------===//
+//===------------------------------- any ----------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+#ifndef _LIBCPP_EXPERIMENTAL_ANY
+#define _LIBCPP_EXPERIMENTAL_ANY
 
-#error "<experimental/any> has been removed. Use <any> instead."
+#include <__config>
+
+#ifdef _LIBCPP_WARNING
+_LIBCPP_WARNING("<experimental/any> has been removed. Use <any> instead.")
+#else
+# warning "<experimental/any> has been removed. Use <any> instead."
+#endif
+
+#endif // _LIBCPP_EXPERIMENTAL_ANY
diff --git a/libcxx/include/experimental/chrono b/libcxx/include/experimental/chrono
index 591cf7160c1..30c7e4a9d5a 100644
--- a/libcxx/include/experimental/chrono
+++ b/libcxx/include/experimental/chrono
@@ -1,11 +1,21 @@
 // -*- C++ -*-
-//===------------------------------ chrono ---------------------------------===//
+//===---------------------------- chrono ----------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+#ifndef _LIBCPP_EXPERIMENTAL_CHRONO
+#define _LIBCPP_EXPERIMENTAL_CHRONO
 
-#error "<experimental/chrono> has been removed. Use <chrono> instead."
+#include <__config>
+
+#ifdef _LIBCPP_WARNING
+_LIBCPP_WARNING("<experimental/chrono> has been removed. Use <chrono> instead.")
+#else
+# warning "<experimental/chrono> has been removed. Use <chrono> instead."
+#endif
+
+#endif // _LIBCPP_EXPERIMENTAL_CHRONO
diff --git a/libcxx/include/experimental/numeric b/libcxx/include/experimental/numeric
index 14a664011b5..19c65313f0f 100644
--- a/libcxx/include/experimental/numeric
+++ b/libcxx/include/experimental/numeric
@@ -7,5 +7,15 @@
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+#ifndef _LIBCPP_EXPERIMENTAL_NUMERIC
+#define _LIBCPP_EXPERIMENTAL_NUMERIC
 
-#error "<experimental/numeric> has been removed. Use <numeric> instead."
+#include <__config>
+
+#ifdef _LIBCPP_WARNING
+_LIBCPP_WARNING("<experimental/numeric> has been removed. Use <numeric> instead.")
+#else
+# warning "<experimental/numeric> has been removed. Use <numeric> instead."
+#endif
+
+#endif // _LIBCPP_EXPERIMENTAL_NUMERIC
diff --git a/libcxx/include/experimental/optional b/libcxx/include/experimental/optional
index d68cefdf6c1..6eb4a2618d2 100644
--- a/libcxx/include/experimental/optional
+++ b/libcxx/include/experimental/optional
@@ -7,5 +7,15 @@
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+#ifndef _LIBCPP_EXPERIMENTAL_OPTIONAL
+#define _LIBCPP_EXPERIMENTAL_OPTIONAL
 
-#error "<experimental/optional> has been removed. Use <optional> instead."
+#include <__config>
+
+#ifdef _LIBCPP_WARNING
+_LIBCPP_WARNING("<experimental/optional> has been removed. Use <optional> instead.")
+#else
+# warning "<experimental/optional> has been removed. Use <optional> instead."
+#endif
+
+#endif // _LIBCPP_EXPERIMENTAL_OPTIONAL
diff --git a/libcxx/include/experimental/ratio b/libcxx/include/experimental/ratio
index 9c2bf2e4624..52c12004dba 100644
--- a/libcxx/include/experimental/ratio
+++ b/libcxx/include/experimental/ratio
@@ -1,11 +1,21 @@
 // -*- C++ -*-
-//===------------------------------ ratio ---------------------------------===//
+//===----------------------------- ratio ----------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+#ifndef _LIBCPP_EXPERIMENTAL_RATIO
+#define _LIBCPP_EXPERIMENTAL_RATIO
 
-#error "<experimental/ratio> has been removed. Use <ratio> instead."
+#include <__config>
+
+#ifdef _LIBCPP_WARNING
+_LIBCPP_WARNING("<experimental/ratio> has been removed. Use <ratio> instead.")
+#else
+# warning "<experimental/ratio> has been removed. Use <ratio> instead."
+#endif
+
+#endif // _LIBCPP_EXPERIMENTAL_RATIO
diff --git a/libcxx/include/experimental/string_view b/libcxx/include/experimental/string_view
index f13bff54d53..100bdfe7273 100644
--- a/libcxx/include/experimental/string_view
+++ b/libcxx/include/experimental/string_view
@@ -3,9 +3,19 @@
 //
 //                     The LLVM Compiler Infrastructure
 //
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+#ifndef _LIBCPP_EXPERIMENTAL_STRING_VIEW
+#define _LIBCPP_EXPERIMENTAL_STRING_VIEW
 
-#error "<experimental/string_view> has been removed. Use <string_view> instead."
+#include <__config>
+
+#ifdef _LIBCPP_WARNING
+_LIBCPP_WARNING("<experimental/string_view> has been removed. Use <string_view> instead.")
+#else
+# warning "<experimental/string_view> has been removed. Use <string_view> instead."
+#endif
+
+#endif // _LIBCPP_EXPERIMENTAL_STRING_VIEW
diff --git a/libcxx/include/experimental/system_error b/libcxx/include/experimental/system_error
index 7937357fa14..1cf84ee0125 100644
--- a/libcxx/include/experimental/system_error
+++ b/libcxx/include/experimental/system_error
@@ -7,5 +7,15 @@
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+#ifndef _LIBCPP_EXPERIMENTAL_SYSTEM_ERROR
+#define _LIBCPP_EXPERIMENTAL_SYSTEM_ERROR
 
-#error "<experimental/system_error> has been removed. Use <system_error> instead."
+#include <__config>
+
+#ifdef _LIBCPP_WARNING
+_LIBCPP_WARNING("<experimental/system_error> has been removed. Use <system_error> instead.")
+#else
+# warning "<experimental/system_error> has been removed. Use <system_error> instead."
+#endif
+
+#endif // _LIBCPP_EXPERIMENTAL_SYSTEM_ERROR
diff --git a/libcxx/include/experimental/tuple b/libcxx/include/experimental/tuple
index 1f37a6293ba..6d71bb559b0 100644
--- a/libcxx/include/experimental/tuple
+++ b/libcxx/include/experimental/tuple
@@ -7,5 +7,15 @@
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+#ifndef _LIBCPP_EXPERIMENTAL_TUPLE
+#define _LIBCPP_EXPERIMENTAL_TUPLE
 
-#error "<experimental/tuple> has been removed. Use <tuple> instead."
+#include <__config>
+
+#ifdef _LIBCPP_WARNING
+_LIBCPP_WARNING("<experimental/tuple> has been removed. Use <tuple> instead.")
+#else
+# warning "<experimental/tuple> has been removed. Use <tuple> instead."
+#endif
+
+#endif // _LIBCPP_EXPERIMENTAL_TUPLE