Major upgrade to Boost.Config symbol visibility macros for shared libraries, based on patches from Jürgen Hunold with mods by Beman Dawes. Upgrade Boost.System to use the new visibility macros. Fixes #3697 and provides foundation for fixing 2114, 2309, etc.

[SVN r62140]

doc/macro_reference.qbk

@@ -317,6 +317,7 @@ void g() { return f(); }
 
 [#config_features]
 
+
 [section Macros that describe optional features]
 
 The following macros describe features that are not required by the C++
@@ -332,10 +333,6 @@ The platform supports BeOS style threads.
 [[`BOOST_HAS_CLOCK_GETTIME`][Platform][
 The platform has the POSIX API `clock_gettime`.
 ]]
-[[`BOOST_HAS_DECLSPEC`][Compiler][
-The compiler uses `__declspec(dllexport)` and `__declspec(dllimport)` to
-export/import symbols from dll's.
-]]
 [[`BOOST_HAS_DIRENT_H`][Platform][
 The platform has the POSIX header `<dirent.h>`.
 ]]
@@ -868,9 +865,98 @@ the configuration.
 [section Macros for libraries with separate source code]
 
 The following macros and helper headers are of use to authors whose libraries
-include separate source code, and are intended to address two issues: fixing
-the ABI of the compiled library, and selecting which compiled library to link
-against based upon the compilers settings.
+include separate source code, and are intended to address several issues:
+
+* Controlling shared library symbol visibility
+* Fixing the ABI of the compiled library
+* Selecting which compiled library to link against based upon the compilers settings
+
+See [@http://svn.boost.org/trac/boost/wiki/Guidelines/Separate Guidelines for Authors of Boost Libraries Containing Separate Source] 
+
+[section Macros controlling shared library symbol visibility]
+
+Some compilers support C++ extensions that control which symbols 
+will be exported from shared libraries such as dynamic shared objects (DSO's) on Unix-like
+systems or dynamic-link libraries (DLL's) on Windows.
+
+The Microsoft VC++ compiler has long supplied 
+`__declspec(dllexport)` and `__declspec(dllimport)` extensions for this purpose,
+as do virtually all other compilers targeting the Windows platform.
+ 
+Modern versions of the GNU GCC compiler provide the `__attribute__((visibility("default")))` 
+extension to indicate that a symbol should be exported. All other symbols may be hidden by using the
+`-fvisibility-hidden` or `-fvisibility-ms-compat` compiler switches.
+
+Boost supplies several macros to make it easier to manage symbol visibility in a way that
+is portable between compilers and operating systems.
+
+[table
+[[Macro       ][Description       ]]
+[[`BOOST_SYMBOL_EXPORT`][
+Defines the syntax of a C++ language extension that indicates a symbol is to be exported from a shared library.
+If the compiler has no such extension, the macro is defined with no replacement text. 
+]]
+[[`BOOST_SYMBOL_IMPORT`][
+Defines the syntax of a C++ language extension that indicates a symbol is to be imported from a shared library.
+If the compiler has no such extension, the macro is defined with no replacement text. 
+]]
+[[`BOOST_SYMBOL_VISIBLE`][
+Defines the syntax of a C++ language extension that indicates a symbol is to be globally visible.
+If the compiler has no such extension, the macro is defined with no replacement text. 
+Needed for classes that are not otherwise exported, but are used by RTTI. Examples include
+class for objects that will be thrown as exceptions or used in dynamic_casts,
+across shared library boundaries. For example, a header-only exception class might look like this:
+``
+  class BOOST_SYMBOL_VISIBLE my_exception : public std::runtime_error { ... };
+`` 
+Without BOOST_SYMBOL_VISIBLE, it would be impossible to catch my_exception thrown from a shared library
+compiled by GCC with the -fvisibility=hidden option.
+]]
+[[`BOOST_HAS_DECLSPEC`][
+The compiler has C++ extensions `__declspec(dllexport)` and `__declspec(dllimport)` to control
+export/import of symbols from shared libraries.
+['Deprecated. This macro is no longer necessary since BOOST_SYMBOL_EXPORT and BOOST_SYMBOL_IMPORT
+are now supplied. It is provided to support legacy code.]
+]]
+]
+
+Typical usage:
+
+[*boost/foo/config.hpp]
+
+    ...
+    #if defined(BOOST_ALL_DYN_LINK) || defined(BOOST_FOO_DYN_LINK)
+    # if defined(BOOST_FOO_SOURCE)
+    #   define BOOST_FOO_DECL BOOST_SYMBOL_EXPORT
+    # else 
+    #   define BOOST_FOO_DECL BOOST_SYMBOL_IMPORT
+    # endif
+    #else
+    # define BOOST_FOO_DECL
+    #endif
+    ...
+ 
+[*boost/foo/foo.hpp] 
+  
+    #include <boost/foo/config.hpp>
+    ...
+    class BOOST_FOO_DECL bar { ... };
+    ...
+    void BOOST_FOO_DECL f();
+    ...
+
+[*boost/libs/foo/src/foo.cpp] 
+   
+    #define BOOST_FOO_SOURCE
+    #include <boost/foo/foo.hpp>    
+    ...
+    void BOOST_FOO_DECL f()
+    {
+      ...
+    }
+    ...
+     
+[endsect]
 
 [section ABI Fixing]
 

include/boost/config/compiler/borland.hpp

@@ -230,8 +230,9 @@
 //
 // all versions support __declspec:
 //
-#ifndef __STRICT_ANSI__
-#  define BOOST_HAS_DECLSPEC
+#if defined(__STRICT_ANSI__)
+// config/platform/win32.hpp will define BOOST_SYMBOL_EXPORT, etc., unless already defined  
+#  define BOOST_SYMBOL_EXPORT
 #endif
 //
 // ABI fixing headers:

include/boost/config/compiler/clang.hpp

@@ -18,12 +18,6 @@
 #  define BOOST_NO_RTTI
 #endif
 
-#if defined(__int32)
-// HACK: Clang only defines the type __int32 in Microsoft-compatibility mode,
-// which means that declspecs are also available
-#  define BOOST_HAS_DECLSPEC
-#endif
-
 #if defined(__int64)
 #  define BOOST_HAS_MS_INT64
 #endif

include/boost/config/compiler/codegear.hpp

@@ -147,8 +147,9 @@
 //
 // all versions support __declspec:
 //
-#if !defined(__STRICT_ANSI__)
-#  define BOOST_HAS_DECLSPEC
+#if defined(__STRICT_ANSI__)
+// config/platform/win32.hpp will define BOOST_SYMBOL_EXPORT, etc., unless already defined  
+#  define BOOST_SYMBOL_EXPORT
 #endif
 //
 // ABI fixing headers:

include/boost/config/compiler/gcc.hpp

@@ -108,6 +108,28 @@
 #if __GNUC__ > 3 || ( __GNUC__ == 3 && __GNUC_MINOR__ >= 1 )
 #define BOOST_HAS_NRVO
 #endif
+
+//
+// Dynamic shared object (DSO) and dynamic-link library (DLL) support
+//
+#if __GNUC__ >= 4
+#  if defined(_WIN32) || defined(__WIN32__) || defined(WIN32)
+     // All Win32 development environments, including 64-bit Windows and MinGW, define 
+     // _WIN32 or one of its variant spellings. Note that Cygwin is a POSIX environment,
+     // so does not define _WIN32 or its variants.
+#    define BOOST_HAS_DECLSPEC
+#    define BOOST_SYMBOL_EXPORT __attribute__((dllexport))
+#    define BOOST_SYMBOL_IMPORT __attribute__((dllimport))
+#  else
+#    define BOOST_SYMBOL_EXPORT __attribute__((visibility("default")))
+#    define BOOST_SYMBOL_IMPORT
+#  endif
+#  define BOOST_SYMBOL_VISIBLE __attribute__((visibility("default")))
+#else
+// config/platform/win32.hpp will define BOOST_SYMBOL_EXPORT, etc., unless already defined  
+#  define BOOST_SYMBOL_EXPORT
+#endif
+
 //
 // RTTI and typeinfo detection is possible post gcc-4.3:
 //

include/boost/config/compiler/visualc.hpp

@@ -163,11 +163,6 @@
 #  define BOOST_NO_RTTI
 #endif
 
-//
-// all versions support __declspec:
-//
-#define BOOST_HAS_DECLSPEC
-
 //
 // C++0x features
 //

include/boost/config/platform/win32.hpp

@@ -21,10 +21,17 @@
 #  define BOOST_NO_SWPRINTF
 #endif
 
-#if !defined(__GNUC__) && !defined(BOOST_HAS_DECLSPEC)
+//  Default defines for BOOST_SYMBOL_EXPORT and BOOST_SYMBOL_IMPORT
+//  If a compiler doesn't support __declspec(dllexport)/__declspec(dllimport),
+//  its boost/config/compiler/ file must define BOOST_SYMBOL_EXPORT and
+//  BOOST_SYMBOL_IMPORT
+#ifndef BOOST_SYMBOL_EXPORT
 #  define BOOST_HAS_DECLSPEC
+#  define BOOST_SYMBOL_EXPORT __declspec(dllexport)
+#  define BOOST_SYMBOL_IMPORT __declspec(dllimport)
 #endif
 
+
 #if defined(__MINGW32__) && ((__MINGW32_MAJOR_VERSION > 2) || ((__MINGW32_MAJOR_VERSION == 2) && (__MINGW32_MINOR_VERSION >= 0)))
 #  define BOOST_HAS_STDINT_H
 #  define __STDC_LIMIT_MACROS

include/boost/config/suffix.hpp

@@ -25,6 +25,19 @@
 #ifndef BOOST_CONFIG_SUFFIX_HPP
 #define BOOST_CONFIG_SUFFIX_HPP
 
+//
+// ensure that visibility macros are always defined, thus symplifying use
+//
+#ifndef BOOST_SYMBOL_EXPORT
+# define BOOST_SYMBOL_EXPORT
+#endif
+#ifndef BOOST_SYMBOL_IMPORT
+# define BOOST_SYMBOL_IMPORT
+#endif
+#ifndef BOOST_SYMBOL_VISIBLE
+# define BOOST_SYMBOL_VISIBLE
+#endif
+
 //
 // look for long long by looking for the appropriate macros in <limits.h>.
 // Note that we use limits.h rather than climits for maximal portability,