Added BOOST_HAS_PRAGMA_ONCE for compilers that support it. The macro was already defined for DMC, but not for other compilers and was not documented.

[SVN r84796]

doc/macro_reference.qbk

@@ -397,6 +397,12 @@ See [@../../../../boost/operators.hpp `<boost/operators.hpp>`] for example.
 The standard library has a partially conforming `std::allocator` class, but
 without any of the member templates.
 ]]
+[[`BOOST_HAS_PRAGMA_ONCE`][Compiler][
+The compiler recognizes the `#pragma once` directive which tells that the
+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_PTHREAD_DELAY_NP`][Platform][
 The platform has the POSIX API `pthread_delay_np`.
 ]]

include/boost/config/compiler/borland.hpp

@@ -283,7 +283,3 @@
 #define BOOST_NO_COMPLETE_VALUE_INITIALIZATION
 
 #define BOOST_COMPILER "Borland C++ version " BOOST_STRINGIZE(__BORLANDC__)
-
-
-
-

include/boost/config/compiler/clang.hpp

@@ -8,6 +8,8 @@
 
 // Clang compiler setup.
 
+#define BOOST_HAS_PRAGMA_ONCE
+
 #if !__has_feature(cxx_exceptions) && !defined(BOOST_NO_EXCEPTIONS)
 #  define BOOST_NO_EXCEPTIONS
 #endif

include/boost/config/compiler/codegear.hpp

@@ -72,6 +72,12 @@
 #  endif
 
 #endif
+
+// Reportedly, #pragma once is supported since C++ Builder 2010
+#if (__CODEGEARC__ >= 0x620)
+#  define BOOST_HAS_PRAGMA_ONCE
+#endif
+
 //
 // C++0x macros:
 //

include/boost/config/compiler/common_edg.hpp

@@ -54,6 +54,11 @@
 #     define BOOST_NO_LONG_LONG
 # endif
 
+// Not sure what version was the first to support #pragma once, but
+// different EDG-based compilers (e.g. Intel) supported it for ages.
+// Add a proper version check if it causes problems.
+#define BOOST_HAS_PRAGMA_ONCE
+
 //
 // C++0x features
 //

include/boost/config/compiler/gcc.hpp

@@ -80,6 +80,11 @@
 #  endif
 #endif
 
+// GCC prior to 3.4 had #pragma once too but it didn't work well with filesystem links
+#if __GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4)
+#define BOOST_HAS_PRAGMA_ONCE
+#endif
+
 #if __GNUC__ < 4 || ( __GNUC__ == 4 && __GNUC_MINOR__ < 4 )
 // Previous versions of GCC did not completely implement value-initialization:
 // GCC Bug 30111, "Value-initialization of POD base class doesn't initialize

include/boost/config/compiler/visualc.hpp

@@ -34,6 +34,10 @@
 // Attempt to suppress VC6 warnings about the length of decorated names (obsolete):
 #pragma warning( disable : 4503 ) // warning: decorated name length exceeded
 
+#if _MSC_VER >= 1020
+#  define BOOST_HAS_PRAGMA_ONCE
+#endif
+
 //
 // versions check:
 // we don't support Visual C++ prior to version 6: