Merge pull request #28 from apolukhin/develop

Added BOOST_HAS_PRAGMA_DETECT_MISSMATCH macro

doc/macro_reference.qbk

@@ -399,6 +399,13 @@ containing header should be included only once while preprocessing the
 current translation unit. The pragma may improve compile times of large projects
 with some compilers.
 ]]
+[[`BOOST_HAS_PRAGMA_DETECT_MISSMATCH`][Compiler][
+The compiler recognizes the `#pragma detect_mismatch("name", "value")` directive which tells that the
+link stage should be terminated with error if values for provided `"name"` missmatch.
+This pragma may be a help in preventing ODR violations and ensuring that different modules
+are compiled with same flags.
+]]
+
 [[`BOOST_HAS_PTHREAD_DELAY_NP`][Platform][
 The platform has the POSIX API `pthread_delay_np`.
 ]]

include/boost/config/compiler/clang.hpp

@@ -10,6 +10,15 @@
 
 #define BOOST_HAS_PRAGMA_ONCE
 
+// Detecting `-fms-extension` compiler flag assuming that _MSC_VER defined when that flag is used.
+#if defined (_MSC_VER) && (__clang_major__ > 3 || (__clang_major__ == 3 && __clang_minor__ >= 4))
+    // Ignoring the checks on APPLE platform because someone made __clang_major__ equal to
+    // LLVM version rather than compiler version.
+#   ifndef __APPLE__
+#       define BOOST_HAS_PRAGMA_DETECT_MISSMATCH
+#   endif
+#endif
+
 // When compiling with clang before __has_extension was defined,
 // even if one writes 'defined(__has_extension) && __has_extension(xxx)',
 // clang reports a compiler error. So the only workaround found is:

include/boost/config/compiler/visualc.hpp

@@ -36,6 +36,9 @@
 
 #define BOOST_HAS_PRAGMA_ONCE
 
+// Will be undefined for old compilers lower in this file
+#define BOOST_HAS_PRAGMA_DETECT_MISSMATCH
+
 //
 // versions check:
 // we don't support Visual C++ prior to version 7.1:
@@ -59,6 +62,7 @@
 
 #if _MSC_VER < 1500  // 140X == VC++ 8.0
 #  define BOOST_NO_MEMBER_TEMPLATE_FRIENDS
+#  undef BOOST_HAS_PRAGMA_DETECT_MISSMATCH
 #endif
 
 #if _MSC_VER < 1600  // 150X == VC++ 9.0