[libc++] Add _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS

[smeenai]

Summary

It's useful to be able to disable visibility annotations entirely; for
example, if we're building libc++ static to include in another library,
and we don't want any libc++ functions getting exported out of that
library. This is a generalization of _LIBCPP_DISABLE_DLL_IMPORT_EXPORT.

[smeenai]

Adding documentation per @EricWF's comment

[EricWF]

There are two usages of _LIBCPP_DISABLE_DLL_IMPORT_EXPORT in CMakeLists.txt and __config_site.in that need to be changed as well.

Also what about users of the existing name _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS? Should we #error to inform them of the change or should we automatically translate it to the new name for them?

[smeenai]

In D26934#603997, @EricWF wrote:

There are two usages of _LIBCPP_DISABLE_DLL_IMPORT_EXPORT in CMakeLists.txt and __config_site.in that need to be changed as well.

Oops, will fix.

Also what about users of the existing name _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS? Should we #error to inform them of the change or should we automatically translate it to the new name for them?

I'd prefer #error; that way we can eventually just drop the macro. Ideally there wouldn't be too many users to begin with, since it was only introduced two months ago, and it hasn't made its way to a release yet.

I'll upload a new diff with those changes later today.

[smeenai]

Addressing comments

[smeenai]

include/__config

513–516

I'd like to remove this before the 4.0 release, if that's all right with you. I don't think there would be many users of the existing macro, and I'd prefer it to not make its way to a release.

[smeenai]

Not changing non-Windows behavior, to make sure I'm not breaking anyone

[EricWF]

In D26934#604325, @smeenai wrote:

I'd prefer #error; that way we can eventually just drop the macro. Ideally there wouldn't be too many users to begin with, since it was only introduced two months ago, and it hasn't made its way to a release yet.

If it hasn't even made it into a release then we probably don't need the #error at all. Feel free to commit with or w/o it.

Either way this LGTM.

CMakeLists.txt

 config_define_if_not(LIBCXX_ENABLE_THREADS _LIBCPP_HAS_NO_THREADS)
 config_define_if_not(LIBCXX_ENABLE_MONOTONIC_CLOCK _LIBCPP_HAS_NO_MONOTONIC_CLOCK)
 config_define_if_not(LIBCXX_ENABLE_THREAD_UNSAFE_C_FUNCTIONS _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS)
 
 config_define_if(LIBCXX_HAS_PTHREAD_API _LIBCPP_HAS_THREAD_API_PTHREAD)
 config_define_if(LIBCXX_HAS_EXTERNAL_THREAD_API _LIBCPP_HAS_THREAD_API_EXTERNAL)
 config_define_if(LIBCXX_HAS_MUSL_LIBC _LIBCPP_HAS_MUSL_LIBC)
 
-# By default libc++ on Windows expects to use a shared library, which requires
-# the headers to use DLL import/export semantics. However when building a
-# static library only we modify the headers to disable DLL import/export.
-if (DEFINED WIN32 AND LIBCXX_ENABLE_STATIC AND NOT LIBCXX_ENABLE_SHARED)
-  message(STATUS "Generating custom __config for non-DLL Windows build")
-  config_define(ON _LIBCPP_DISABLE_DLL_IMPORT_EXPORT)
+# By default libc++ expects to use a shared library, so we annotate the headers
+# with visibility specifiers. However when building a static library only we
+# modify the headers to disable these annotations.
+if (LIBCXX_ENABLE_STATIC AND NOT LIBCXX_ENABLE_SHARED)
+  message(STATUS "Generating custom __config for non-shared build")
+  config_define(ON _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
 endif()
 
 if (LIBCXX_NEEDS_SITE_CONFIG)
   configure_file(
     include/__config_site.in
     ${LIBCXX_BINARY_DIR}/__config_site
     @ONLY)
   # Provide the config definitions by included the generated __config_site

docs/UsingLibcxx.rst

**_LIBCPP_DEBUG**:
   the program.
 
   Note that this option has no effect on libc++'s ABI
 
 **_LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS**:
   This macro is used to enable -Wthread-safety annotations on libc++'s
   ``std::mutex`` and ``std::lock_guard``. By default these annotations are
   disabled and must be manually enabled by the user.
+
+**_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS**:
+  This macro is used to disable all visibility annotations inside libc++.
+  Defining this macro and then building libc++ with hidden visibility gives a
+  build of libc++ which does not export any symbols, which can be useful when
+  building statically for inclusion into another library.

include/__config

 }
 
 #define _LIBCPP_HAS_NO_ASAN
 
 #endif // __clang__ || __GNUC__ || _MSC_VER || __IBMCPP__
 
 
 #ifdef _WIN32
 #if defined(_LIBCPP_DISABLE_DLL_IMPORT_EXPORT)
+// this can be removed once any existing users have switched to the new macro
+# error "Use _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS instead of _LIBCPP_DISABLE_DLL_IMPORT_EXPORT"
+#endif
+#if defined(_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
 # define _LIBCPP_DLL_VIS
 # define _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS
 # define _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS
 # define _LIBCPP_OVERRIDABLE_FUNC_VIS
 #elif defined(_LIBCPP_BUILDING_LIBRARY)
 # define _LIBCPP_DLL_VIS __declspec(dllexport)
 # define _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS
 # define _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS _LIBCPP_DLL_VIS

 #else
 # define _LIBCPP_INLINE_VISIBILITY __attribute__ ((__always_inline__))
 # define _LIBCPP_ALWAYS_INLINE     __attribute__ ((__always_inline__))
 # define _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY __attribute__ ((__always_inline__))
 #endif
 #endif // _WIN32
 
 #ifndef _LIBCPP_HIDDEN
+#if !defined(_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
 #define _LIBCPP_HIDDEN __attribute__ ((__visibility__("hidden")))
+#else
+#define _LIBCPP_HIDDEN
+#endif
 #endif
 
 #ifndef _LIBCPP_FUNC_VIS
+#if !defined(_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
 #define _LIBCPP_FUNC_VIS __attribute__ ((__visibility__("default")))
+#else
+#define _LIBCPP_FUNC_VIS
+#endif
 #endif
 
 #ifndef _LIBCPP_TYPE_VIS
-#  if __has_attribute(__type_visibility__)
-#    define _LIBCPP_TYPE_VIS __attribute__ ((__type_visibility__("default")))
-#  else
-#    define _LIBCPP_TYPE_VIS __attribute__ ((__visibility__("default")))
-#  endif
+#  if !defined(_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
+#    if __has_attribute(__type_visibility__)
+#      define _LIBCPP_TYPE_VIS __attribute__ ((__type_visibility__("default")))
+#    else
+#      define _LIBCPP_TYPE_VIS __attribute__ ((__visibility__("default")))
+#    endif
+#  else
+#    define _LIBCPP_TYPE_VIS
+#  endif
 #endif
 
 #ifndef _LIBCPP_TYPE_VIS_ONLY
 # define _LIBCPP_TYPE_VIS_ONLY _LIBCPP_TYPE_VIS
 #endif
 
 #ifndef _LIBCPP_FUNC_VIS_ONLY
 # define _LIBCPP_FUNC_VIS_ONLY _LIBCPP_FUNC_VIS
 #endif
 
 #ifndef _LIBCPP_OVERRIDABLE_FUNC_VIS
 # define _LIBCPP_OVERRIDABLE_FUNC_VIS _LIBCPP_FUNC_VIS
 #endif
 
 #ifndef _LIBCPP_EXCEPTION_ABI
+#if !defined(_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
 #define _LIBCPP_EXCEPTION_ABI __attribute__ ((__visibility__("default")))
+#else
+#define _LIBCPP_EXCEPTION_ABI
+#endif
 #endif
 
 #ifndef _LIBCPP_ENUM_VIS
-#  if __has_attribute(__type_visibility__)
+#  if !defined(_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS) && __has_attribute(__type_visibility__)
 #    define _LIBCPP_ENUM_VIS __attribute__ ((__type_visibility__("default")))
 #  else
 #    define _LIBCPP_ENUM_VIS
 #  endif
 #endif
 
 #ifndef _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS
-#  if __has_attribute(__type_visibility__)
+#  if !defined(_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS) && __has_attribute(__type_visibility__)
 #    define _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __attribute__ ((__type_visibility__("default")))
 #  else
 #    define _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS
 #  endif
 #endif
 
 #ifndef _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS
 #  define _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS
 #endif
 
 #ifndef _LIBCPP_INLINE_VISIBILITY
+#if !defined(_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
 #define _LIBCPP_INLINE_VISIBILITY __attribute__ ((__visibility__("hidden"), __always_inline__))
+#else
+#define _LIBCPP_INLINE_VISIBILITY __attribute__ ((__always_inline__))
+#endif
 #endif
 
 #ifndef _LIBCPP_ALWAYS_INLINE
+#if !defined(_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
 #define _LIBCPP_ALWAYS_INLINE  __attribute__ ((__visibility__("hidden"), __always_inline__))
+#else
+#define _LIBCPP_ALWAYS_INLINE  __attribute__ ((__always_inline__))
+#endif
 #endif
 
 #ifndef _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY
-# define _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY __attribute__((__visibility__("default"), __always_inline__))
+# if !defined(_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS)
+#  define _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY __attribute__((__visibility__("default"), __always_inline__))
+# else
+#  define _LIBCPP_EXTERN_TEMPLATE_INLINE_VISIBILITY __attribute__((__always_inline__))
+# endif
 #endif
 
 #ifndef _LIBCPP_PREFERRED_OVERLOAD
 #  if __has_attribute(__enable_if__)
 #    define _LIBCPP_PREFERRED_OVERLOAD __attribute__ ((__enable_if__(true, "")))
 #  endif
 #endif
 

include/__config_site.in

 #cmakedefine _LIBCPP_HAS_NO_STDIN
 #cmakedefine _LIBCPP_HAS_NO_STDOUT
 #cmakedefine _LIBCPP_HAS_NO_THREADS
 #cmakedefine _LIBCPP_HAS_NO_MONOTONIC_CLOCK
 #cmakedefine _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
 #cmakedefine _LIBCPP_HAS_MUSL_LIBC
 #cmakedefine _LIBCPP_HAS_THREAD_API_PTHREAD
 #cmakedefine _LIBCPP_HAS_THREAD_API_EXTERNAL
-#cmakedefine _LIBCPP_DISABLE_DLL_IMPORT_EXPORT
+#cmakedefine _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS
 
 #endif // _LIBCPP_CONFIG_SITE