[libc++] Recategorize additional instantiations in the dylib as availability macros

Adding additional instantiations to the dylib isn't actually an ABI break as long as programs targeting an older dylib don't start to depend on them. Making additional instantiations a matter of availability allows us to add them without an ABI break.

Reviewed By: #libc, ldionne, Mordante

Spies: arichardson, ldionne, Mordante, libcxx-commits

Differential Revision: https://reviews.llvm.org/D154796

Author: philnik777

libcxx/include/__availability

@@ -179,6 +179,17 @@
 // #   define _LIBCPP_AVAILABILITY_HAS_NO_TZDB
 #   define _LIBCPP_AVAILABILITY_TZDB
 
+// Enable additional explicit instantiations of iostreams components. This
+// reduces the number of weak definitions generated in programs that use
+// iostreams by providing a single strong definition in the shared library.
+//
+// TODO: Enable additional explicit instantiations on GCC once it supports exclude_from_explicit_instantiation,
+//       or once libc++ doesn't use the attribute anymore.
+// TODO: Enable them on Windows once https://llvm.org/PR41018 has been fixed.
+#if defined(_LIBCPP_COMPILER_GCC) || defined(_WIN32)
+#  define _LIBCPP_AVAILABILITY_HAS_NO_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1
+#endif
+
 #elif defined(__APPLE__)
 
     // shared_mutex and shared_timed_mutex
@@ -356,6 +367,12 @@
 #  define _LIBCPP_AVAILABILITY_HAS_NO_TZDB
 #  define _LIBCPP_AVAILABILITY_TZDB __attribute__((unavailable))
 
+#  if (defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 120000)   || \
+      (defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__) && __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ < 150000) || \
+      (defined(__ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__) && __ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__ < 150000)         || \
+      (defined(__ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__) && __ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__ < 80000)
+#    define _LIBCPP_AVAILABILITY_HAS_NO_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1
+#  endif
 #else
 
 // ...New vendors can add availability markup here...

libcxx/include/__config

@@ -193,11 +193,6 @@
 #  endif
 
 #  if defined(_LIBCPP_BUILDING_LIBRARY) || _LIBCPP_ABI_VERSION >= 2
-// Enable additional explicit instantiations of iostreams components. This
-// reduces the number of weak definitions generated in programs that use
-// iostreams by providing a single strong definition in the shared library.
-#    define _LIBCPP_ABI_ENABLE_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1
-
 // Define a key function for `bad_function_call` in the library, to centralize
 // its vtable and typeinfo to libc++ rather than having all other libraries
 // using that class define their own copies.

libcxx/include/fstream

@@ -1734,7 +1734,7 @@ basic_fstream<_CharT, _Traits>::close()
         this->setstate(ios_base::failbit);
 }
 
-#if defined(_LIBCPP_ABI_ENABLE_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1)
+#ifndef _LIBCPP_AVAILABILITY_HAS_NO_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ifstream<char>;
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ofstream<char>;
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_filebuf<char>;

libcxx/include/sstream

@@ -1192,7 +1192,7 @@ swap(basic_stringstream<_CharT, _Traits, _Allocator>& __x,
     __x.swap(__y);
 }
 
-#if defined(_LIBCPP_ABI_ENABLE_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1)
+#ifndef _LIBCPP_AVAILABILITY_HAS_NO_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_stringbuf<char>;
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_stringstream<char>;
 extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ostringstream<char>;

libcxx/src/ios.instantiations.cpp

@@ -31,7 +31,7 @@ template class _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS basic_ostream<wchar_t>;
 #endif
 
 // Additional instantiations added later. Whether programs rely on these being
-// available is protected by _LIBCPP_ABI_ENABLE_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1.
+// available is protected by _LIBCPP_AVAILABILITY_HAS_NO_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1.
 template class _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS basic_stringbuf<char>;
 template class _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS basic_stringstream<char>;
 template class _LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS basic_ostringstream<char>;