[libc++] Towards a simpler extern template story in libc++

[ldionne]

Summary

The flexibility around extern template instantiation declarations in
libc++ result in a very complicated model, especially when support for
slightly different configurations (like the debug mode or assertions
in the dylib) are taken into account. That results in unexpected bugs
like http://llvm.org/PR50534 (and there have been multiple similar
bugs in the past, notably around the debug mode).

This patch gets rid of the _LIBCPP_DISABLE_EXTERN_TEMPLATE knob, which
I don't think is fundamental. Indeed, the motivation for that knob was to
avoid taking a dependency on the library, however that can be done better
by linking against the static library instead. And in fact, some parts of
the headers will always depend on things defined in the library, which
defeats the original goal of _LIBCPP_DISABLE_EXTERN_TEMPLATE.

[ldionne]

This patch does have the problem that if we want to be able to enable the debugging mode, the library has to have been built with the debug mode enabled, which wasn't the case previously (but instead we had blatant ODR issues that might just not have bitten anyone so far).

[• Quuxplusone]

libcxx/docs/ReleaseNotes.rst

81–84

@ldionne wrote:

does have the problem that if we want to be able to enable the debugging mode, the library has to have been built with the debug mode enabled, which wasn't the case previously

It was always the case for debug iterators. I wrote an email to the libcxx-dev mailing list on 2021-05-01 and still haven't seen any reply to it.

libcxx/include/__locale

343

This PR basically LGTM. I do want to raise the question of greppability: The old macros let you grep -l _LIBCPP_EXTERN_TEMPLATE to find these sneaky declarations. The new code makes you grep -l extern.template instead. This seems fine to me; do you agree?

FYI, some places already use extern template (for function templates only):

libcxx/include/locale:extern template _LIBCPP_FUNC_VIS time_base::dateorder __time_get_storage<_CharT>::__do_date_order() const; \
libcxx/include/locale:extern template _LIBCPP_FUNC_VIS __time_get_storage<_CharT>::__time_get_storage(const char*); \
libcxx/include/locale:extern template _LIBCPP_FUNC_VIS __time_get_storage<_CharT>::__time_get_storage(const string&); \
libcxx/include/locale:extern template _LIBCPP_FUNC_VIS void __time_get_storage<_CharT>::init(const ctype<_CharT>&); \
libcxx/include/locale:extern template _LIBCPP_FUNC_VIS __time_get_storage<_CharT>::string_type __time_get_storage<_CharT>::__analyze(char, const ctype<_CharT>&); \

[ldionne]

Rebase onto main. This is now unrelated to fixing http://llvm.org/PR50534.

libcxx/docs/ReleaseNotes.rst

81–84

Thanks for that, please see my reply.

libcxx/include/__locale

343

do you agree?

Yes, I think that's fine (and in fact a lot more straightforward than before).

[ldionne]

@smeenai What do you think about this (since you added the knob in the first place)? Do you agree with my assessment that the goal of avoiding a dependency on the library isn't met by _LIBCPP_EXTERN_TEMPLATE alone?

[smeenai]

In D103960#2808574, @ldionne wrote:

@smeenai What do you think about this (since you added the knob in the first place)? Do you agree with my assessment that the goal of avoiding a dependency on the library isn't met by _LIBCPP_EXTERN_TEMPLATE alone?

Sorry, this got buried in my inbox!

This looks like a great simplification to me. The work that originally needed this knob is defunct, and we were actually bitten by it in another place (something with the iostream static initializers got messed up IIRC). Doing a static link if you don't want the library dependency (and making it hermetic if you want it to be self-contained) SGTM.

[ldionne]

In D103960#2903608, @smeenai wrote:

In D103960#2808574, @ldionne wrote:

@smeenai What do you think about this (since you added the knob in the first place)? Do you agree with my assessment that the goal of avoiding a dependency on the library isn't met by _LIBCPP_EXTERN_TEMPLATE alone?

Sorry, this got buried in my inbox!

This looks like a great simplification to me. The work that originally needed this knob is defunct, and we were actually bitten by it in another place (something with the iostream static initializers got messed up IIRC). Doing a static link if you don't want the library dependency (and making it hermetic if you want it to be self-contained) SGTM.

No worries, and awesome, I'm quite happy to make this simplification.

I'll need to fix a few things with the debug mode first though, since we currently assume that we can run debug mode tests against the non-debug-mode-built dylib, which doesn't work.

[ldionne]

Rebase onto main

[ldionne]

Rebase onto main. We still haven't fixed the underlying issues with the debug mode (it requires the dylib to have been built with support for the debug mode), but I'm curious to see what fails, if anything.

[ldionne]

Rebase onto main. Now that the debug mode is configure-time only, I think this should work.

[philnik]

I really like this. I've got just one question: Why are the extern declarations for string different than for every other extern template class declaration?

[ldionne]

Poke CI.

[ldionne]

In D103960#3567171, @philnik wrote:

I really like this. I've got just one question: Why are the extern declarations for string different than for every other extern template class declaration?

Do you mean why do we use macros for them? It's just that there's a really long list of methods to declare, so using macros avoids repeating them. However, TBH it's not clear to me that it's actually better, since this sort of duplication isn't super harmful anyways. I think I'd be OK with changing that and repeating the list of instantiated methods in a separate patch.

[philnik]

In D103960#3568852, @ldionne wrote:

In D103960#3567171, @philnik wrote:

I really like this. I've got just one question: Why are the extern declarations for string different than for every other extern template class declaration?

Do you mean why do we use macros for them? It's just that there's a really long list of methods to declare, so using macros avoids repeating them. However, TBH it's not clear to me that it's actually better, since this sort of duplication isn't super harmful anyways. I think I'd be OK with changing that and repeating the list of instantiated methods in a separate patch.

I mean why aren't we using extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_string<char, char_traits<char>, allocator<char>> etc.? It's quite surprising IMO that string is the one class where we don't do that. Just to try it out I removed the explicit list and replaced it with the normal extern template stuff. It turns out that __init_copy_ctor_external, __erase_external_with_move, __assign_external and __assign_short aren't marked as _LIBCPP_HIDE_FROM_ABI but are also not exported from the dylib. Other than __assign_short I think these are intended to go into the dylib. Wheter they are or aren't supposed to go into the dylib doesn't really matter right now. My point is that the explicit list causes inconsistencies and doesn't seem to have any actual uses. It's of course possible that I'm missing something.'that makes the explicit lists super useful.

libcxx/docs/DesignDocs/VisibilityMacros.rst

**_LIBCPP_ENUM_VIS**
 
   **GCC Behavior**: GCC un-hides the typeinfo for enumerations by default, even
   if `-fvisibility=hidden` is specified. Additionally applying a visibility
   attribute to an enum class results in a warning. The macro has an empty
   definition with GCC.
 
 **_LIBCPP_EXTERN_TEMPLATE_TYPE_VIS**
   Mark the member functions, typeinfo, and vtable of the type named in
-  a `_LIBCPP_EXTERN_TEMPLATE` declaration as being exported by the libc++ library.
+  an extern template declaration as being exported by the libc++ library.
   This attribute must be specified on all extern class template declarations.
 
   This macro is used to override the `_LIBCPP_TEMPLATE_VIS` attribute
   specified on the primary template and to export the member functions produced
   by the explicit instantiation in the dylib.
 
   **Windows Behavior**: `extern template` and `dllexport` are fundamentally
   incompatible *on a class template* on Windows; the former suppresses

libcxx/docs/ReleaseNotes.rst

- The implementation of the function ``std::to_chars`` for integral types has
   moved from the dylib to the header. This means the function no longer has a
   minimum deployment target.
 
 API Changes
 -----------
 
 - The ``_LIBCPP_ABI_UNSTABLE`` macro has been removed in favour of setting
   ``_LIBCPP_ABI_VERSION=2``. This should not have any impact on users because
   they were not supposed to set ``_LIBCPP_ABI_UNSTABLE`` manually, however we
   still feel that it is worth mentioning in the release notes in case some users
   had been doing it.
 
 - The header ``<experimental/filesystem>`` has been removed. Instead, use
   ``<filesystem>`` header. The associated macro
   ``_LIBCPP_DEPRECATED_EXPERIMENTAL_FILESYSTEM`` has also been removed.
 
 - Some libc++ headers no longer transitively include all of:
     - ``<algorithm>``
     - ``<chrono>``
     - ``<functional>``

 
 - The ``_LIBCPP_DEBUG`` macro is not supported anymore. It will be honoured until
   LLVM 16, and then it will be an error to define that macro. To enable basic
   assertions (previously ``_LIBCPP_DEBUG=0``), please use ``_LIBCPP_ENABLE_ASSERTIONS=1``.
   To enable the debug mode (previously ``_LIBCPP_DEBUG=1|2``), please ensure that
   the library has been built with support for the debug mode, and it will be
   enabled automatically (no need to define ``_LIBCPP_DEBUG``).
 
+- The ``_LIBCPP_DISABLE_EXTERN_TEMPLATE`` macro is not honored anymore when defined by
+  users of libc++. Instead, users not wishing to take a dependency on libc++ should link
+  against the static version of libc++, which will result in no dependency being
+  taken against the shared library.
+
 ABI Changes
 -----------
 
 - The ``_LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION`` macro controlling whether we use an
   emulation for ``std::nullptr_t`` in C++03 mode has been removed. After this change,
   ``_LIBCPP_ABI_USE_CXX03_NULLPTR_EMULATION`` will not be honoured anymore and there
   will be no way to opt back into the C++03 emulation of ``std::nullptr_t``.
 

libcxx/docs/UsingLibcxx.rst

**_LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS**:
   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.
 
-**_LIBCPP_DISABLE_EXTERN_TEMPLATE**:
-  This macro is used to disable extern template declarations in the libc++
-  headers. The intended use case is for clients who wish to use the libc++
-  headers without taking a dependency on the libc++ library itself.
-
 **_LIBCPP_DISABLE_ADDITIONAL_DIAGNOSTICS**:
   This macro disables the additional diagnostics generated by libc++ using the
   `diagnose_if` attribute. These additional diagnostics include checks for:
 
     * Giving `set`, `map`, `multiset`, `multimap` and their `unordered_`
       counterparts a comparator which is not const callable.
     * Giving an unordered associative container a hasher that is not const
       callable.

libcxx/include/__algorithm/sort.h

 }
 
 template <class _Compare, class _Tp>
 inline _LIBCPP_INLINE_VISIBILITY void __sort(_Tp** __first, _Tp** __last, __less<_Tp*>&) {
   __less<uintptr_t> __comp;
   _VSTD::__sort<__less<uintptr_t>&, uintptr_t*>((uintptr_t*)__first, (uintptr_t*)__last, __comp);
 }
 
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<char>&, char*>(char*, char*, __less<char>&))
+extern template _LIBCPP_FUNC_VIS void __sort<__less<char>&, char*>(char*, char*, __less<char>&);
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<wchar_t>&, wchar_t*>(wchar_t*, wchar_t*, __less<wchar_t>&))
+extern template _LIBCPP_FUNC_VIS void __sort<__less<wchar_t>&, wchar_t*>(wchar_t*, wchar_t*, __less<wchar_t>&);
 #endif
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<signed char>&, signed char*>(signed char*, signed char*, __less<signed char>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<unsigned char>&, unsigned char*>(unsigned char*, unsigned char*, __less<unsigned char>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<short>&, short*>(short*, short*, __less<short>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<unsigned short>&, unsigned short*>(unsigned short*, unsigned short*, __less<unsigned short>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<int>&, int*>(int*, int*, __less<int>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<unsigned>&, unsigned*>(unsigned*, unsigned*, __less<unsigned>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<long>&, long*>(long*, long*, __less<long>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<unsigned long>&, unsigned long*>(unsigned long*, unsigned long*, __less<unsigned long>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<long long>&, long long*>(long long*, long long*, __less<long long>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<unsigned long long>&, unsigned long long*>(unsigned long long*, unsigned long long*, __less<unsigned long long>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<float>&, float*>(float*, float*, __less<float>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<double>&, double*>(double*, double*, __less<double>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void __sort<__less<long double>&, long double*>(long double*, long double*, __less<long double>&))
+extern template _LIBCPP_FUNC_VIS void __sort<__less<signed char>&, signed char*>(signed char*, signed char*, __less<signed char>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<unsigned char>&, unsigned char*>(unsigned char*, unsigned char*, __less<unsigned char>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<short>&, short*>(short*, short*, __less<short>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<unsigned short>&, unsigned short*>(unsigned short*, unsigned short*, __less<unsigned short>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<int>&, int*>(int*, int*, __less<int>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<unsigned>&, unsigned*>(unsigned*, unsigned*, __less<unsigned>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<long>&, long*>(long*, long*, __less<long>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<unsigned long>&, unsigned long*>(unsigned long*, unsigned long*, __less<unsigned long>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<long long>&, long long*>(long long*, long long*, __less<long long>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<unsigned long long>&, unsigned long long*>(unsigned long long*, unsigned long long*, __less<unsigned long long>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<float>&, float*>(float*, float*, __less<float>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<double>&, double*>(double*, double*, __less<double>&);
+extern template _LIBCPP_FUNC_VIS void __sort<__less<long double>&, long double*>(long double*, long double*, __less<long double>&);
 
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<char>&, char*>(char*, char*, __less<char>&))
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<char>&, char*>(char*, char*, __less<char>&);
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<wchar_t>&, wchar_t*>(wchar_t*, wchar_t*, __less<wchar_t>&))
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<wchar_t>&, wchar_t*>(wchar_t*, wchar_t*, __less<wchar_t>&);
 #endif
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<signed char>&, signed char*>(signed char*, signed char*, __less<signed char>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<unsigned char>&, unsigned char*>(unsigned char*, unsigned char*, __less<unsigned char>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<short>&, short*>(short*, short*, __less<short>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<unsigned short>&, unsigned short*>(unsigned short*, unsigned short*, __less<unsigned short>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<int>&, int*>(int*, int*, __less<int>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<unsigned>&, unsigned*>(unsigned*, unsigned*, __less<unsigned>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<long>&, long*>(long*, long*, __less<long>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<unsigned long>&, unsigned long*>(unsigned long*, unsigned long*, __less<unsigned long>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<long long>&, long long*>(long long*, long long*, __less<long long>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<unsigned long long>&, unsigned long long*>(unsigned long long*, unsigned long long*, __less<unsigned long long>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<float>&, float*>(float*, float*, __less<float>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<double>&, double*>(double*, double*, __less<double>&))
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<long double>&, long double*>(long double*, long double*, __less<long double>&))
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<signed char>&, signed char*>(signed char*, signed char*, __less<signed char>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<unsigned char>&, unsigned char*>(unsigned char*, unsigned char*, __less<unsigned char>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<short>&, short*>(short*, short*, __less<short>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<unsigned short>&, unsigned short*>(unsigned short*, unsigned short*, __less<unsigned short>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<int>&, int*>(int*, int*, __less<int>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<unsigned>&, unsigned*>(unsigned*, unsigned*, __less<unsigned>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<long>&, long*>(long*, long*, __less<long>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<unsigned long>&, unsigned long*>(unsigned long*, unsigned long*, __less<unsigned long>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<long long>&, long long*>(long long*, long long*, __less<long long>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<unsigned long long>&, unsigned long long*>(unsigned long long*, unsigned long long*, __less<unsigned long long>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<float>&, float*>(float*, float*, __less<float>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<double>&, double*>(double*, double*, __less<double>&);
+extern template _LIBCPP_FUNC_VIS bool __insertion_sort_incomplete<__less<long double>&, long double*>(long double*, long double*, __less<long double>&);
 
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS unsigned __sort5<__less<long double>&, long double*>(long double*, long double*, long double*, long double*, long double*, __less<long double>&))
+extern template _LIBCPP_FUNC_VIS unsigned __sort5<__less<long double>&, long double*>(long double*, long double*, long double*, long double*, long double*, __less<long double>&);
 
 template <class _RandomAccessIterator, class _Compare>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 void
 sort(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compare __comp) {
   _LIBCPP_DEBUG_RANDOMIZE_RANGE(__first, __last);
   typedef typename __comp_ref_type<_Compare>::type _Comp_ref;
   if (__libcpp_is_constant_evaluated()) {
     _VSTD::__partial_sort<_Comp_ref>(__first, __last, __last, _Comp_ref(__comp));

libcxx/include/__config

#  define _LIBCPP_DECLARE_STRONG_ENUM_EPILOG(x) \
      _LIBCPP_INLINE_VISIBILITY explicit x(int __v) : __v_(static_cast<__lx>(__v)) {} \
      _LIBCPP_INLINE_VISIBILITY operator int() const {return __v_;} \
      };
 #else  // _LIBCPP_CXX03_LANG
 #  define _LIBCPP_DECLARE_STRONG_ENUM(x) enum class _LIBCPP_ENUM_VIS x
 #  define _LIBCPP_DECLARE_STRONG_ENUM_EPILOG(x)
 #endif // _LIBCPP_CXX03_LANG
 
-// Libc++ allows disabling extern template instantiation declarations by
-// means of users defining _LIBCPP_DISABLE_EXTERN_TEMPLATE.
-//
-// TODO: Remove _LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE, which is not needed
-//       since the Debug mode is a configuration-time property.
-#if defined(_LIBCPP_DISABLE_EXTERN_TEMPLATE)
-#   define _LIBCPP_EXTERN_TEMPLATE(...) /* nothing */
-#   define _LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(...) /* nothing */
-#else
-#   define _LIBCPP_EXTERN_TEMPLATE(...) extern template __VA_ARGS__;
-#   define _LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(...) extern template __VA_ARGS__;
-#endif
-
 #if defined(__APPLE__) || defined(__FreeBSD__) || defined(_LIBCPP_MSVCRT_LIKE) || \
     defined(__sun__) || defined(__NetBSD__)
 #define _LIBCPP_LOCALE__L_EXTENSIONS 1
 #endif
 
 #ifdef __FreeBSD__
 #define _DECLARE_C99_LDBL_MATH 1
 #endif

libcxx/include/__locale

collate<_CharT>::do_hash(const char_type* __lo, const char_type* __hi) const
     {
         __h = (__h << 4) + static_cast<size_t>(*__p);
         size_t __g = __h & __mask;
         __h ^= __g | (__g >> __sr);
     }
     return static_cast<long>(__h);
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS collate<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS collate<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS collate<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS collate<wchar_t>;
 #endif
 
 // template <class CharT> class collate_byname;
 
 template <class _CharT> class _LIBCPP_TEMPLATE_VIS collate_byname;
 
 template <>
 class _LIBCPP_TYPE_VIS collate_byname<char>
     : public collate<char>

 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
 template <class _InternT, class _ExternT, class _StateT>
 codecvt_byname<_InternT, _ExternT, _StateT>::~codecvt_byname()
 {
 }
 _LIBCPP_SUPPRESS_DEPRECATED_POP
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char, char, mbstate_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char, char, mbstate_t>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<wchar_t, char, mbstate_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<wchar_t, char, mbstate_t>;
 #endif
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_DEPRECATED_IN_CXX20 _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char16_t, char, mbstate_t>) // deprecated in C++20
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_DEPRECATED_IN_CXX20 _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char32_t, char, mbstate_t>) // deprecated in C++20
+extern template class _LIBCPP_DEPRECATED_IN_CXX20 _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char16_t, char, mbstate_t>; // deprecated in C++20
+extern template class _LIBCPP_DEPRECATED_IN_CXX20 _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char32_t, char, mbstate_t>; // deprecated in C++20
 #ifndef _LIBCPP_HAS_NO_CHAR8_T
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char16_t, char8_t, mbstate_t>) // C++20
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char32_t, char8_t, mbstate_t>) // C++20
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char16_t, char8_t, mbstate_t>; // C++20
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS codecvt_byname<char32_t, char8_t, mbstate_t>; // C++20
 #endif
 
 template <size_t _Np>
 struct __narrow_to_utf8
 {
     template <class _OutputIterator, class _CharT>
     _OutputIterator
     operator()(_OutputIterator __s, const _CharT* __wb, const _CharT* __we) const;

libcxx/include/fstream

 void
 basic_fstream<_CharT, _Traits>::close()
 {
     if (__sb_.close() == nullptr)
         this->setstate(ios_base::failbit);
 }
 
 #if defined(_LIBCPP_ABI_ENABLE_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1)
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ifstream<char>)
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ofstream<char>)
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_filebuf<char>)
+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>;
 #endif
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP_FSTREAM

libcxx/include/istream

#ifndef _LIBCPP_NO_EXCEPTIONS
             }
         }
 #endif
         __is.setstate(__state);
     }
     return __is;
 }
 
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_istream<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_istream<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_istream<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_istream<wchar_t>;
 #endif
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_iostream<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_iostream<char>;
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP_ISTREAM

libcxx/include/locale

__num_get<_CharT>::__stage2_float_loop(_CharT __ct, bool& __in_units, char& __exp, char* __a, char*& __a_end,
     }
     *__a_end++ = __x;
     if (__f >= 22)
         return 0;
     ++__dc;
     return 0;
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(struct _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __num_get<char>)
+extern template struct _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __num_get<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(struct _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __num_get<wchar_t>)
+extern template struct _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __num_get<wchar_t>;
 #endif
 
 template <class _CharT, class _InputIterator = istreambuf_iterator<_CharT> >
 class _LIBCPP_TEMPLATE_VIS num_get
     : public locale::facet,
       private __num_get<_CharT>
 {
 public:
num_get<_CharT, _InputIterator>::do_get(iter_type __b, iter_type __e,
     if (__libcpp_sscanf_l(__buf.c_str(), _LIBCPP_GET_C_LOCALE, "%p", &__v) != 1)
         __err = ios_base::failbit;
     // EOF checked
     if (__b == __e)
         __err |= ios_base::eofbit;
     return __b;
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS num_get<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS num_get<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS num_get<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS num_get<wchar_t>;
 #endif
 
 struct _LIBCPP_TYPE_VIS __num_put_base
 {
 protected:
     static void __format_int(char* __fmt, const char* __len, bool __signd,
                              ios_base::fmtflags __flags);
     static bool __format_float(char* __fmt, const char* __len,
__num_put<_CharT>::__widen_and_group_float(char* __nb, char* __np, char* __ne,
     __ct.widen(__nf, __ne, __oe);
     __oe += __ne - __nf;
     if (__np == __ne)
         __op = __oe;
     else
         __op = __ob + (__np - __nb);
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(struct _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __num_put<char>)
+extern template struct _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __num_put<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(struct _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __num_put<wchar_t>)
+extern template struct _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __num_put<wchar_t>;
 #endif
 
 template <class _CharT, class _OutputIterator = ostreambuf_iterator<_CharT> >
 class _LIBCPP_TEMPLATE_VIS num_put
     : public locale::facet,
       private __num_put<_CharT>
 {
 public:
if (__np == __ne)
         __op = __oe;
     else
         __op = __o + (__np - __nar);
     // [__o, __oe) contains wide number
     // Stage 3 & 4
     return __pad_and_output(__s, __o, __op, __oe, __iob, __fl);
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS num_put<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS num_put<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS num_put<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS num_put<wchar_t>;
 #endif
 
 template <class _CharT, class _InputIterator>
 _LIBCPP_HIDDEN
 int
 __get_up_to_n_digits(_InputIterator& __b, _InputIterator __e,
                      ios_base::iostate& __err, const ctype<_CharT>& __ct, int __n)
 {
case '%':
         __get_percent(__b, __e, __err, __ct);
         break;
     default:
         __err |= ios_base::failbit;
     }
     return __b;
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_get<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_get<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_get<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_get<wchar_t>;
 #endif
 
 class _LIBCPP_TYPE_VIS __time_get
 {
 protected:
     locale_t __loc_;
 
     __time_get(const char* __nm);
private:
     _LIBCPP_INLINE_VISIBILITY
     virtual const string_type& __r() const      {return this->__r_;}
     _LIBCPP_INLINE_VISIBILITY
     virtual const string_type& __x() const      {return this->__x_;}
     _LIBCPP_INLINE_VISIBILITY
     virtual const string_type& __X() const      {return this->__X_;}
 };
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_get_byname<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_get_byname<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_get_byname<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_get_byname<wchar_t>;
 #endif
 
 class _LIBCPP_TYPE_VIS __time_put
 {
     locale_t __loc_;
 protected:
     _LIBCPP_INLINE_VISIBILITY __time_put() : __loc_(_LIBCPP_GET_C_LOCALE) {}
     __time_put(const char* __nm);

 {
     char_type __nar[100];
     char_type* __nb = __nar;
     char_type* __ne = __nb + 100;
     __do_put(__nb, __ne, __tm, __fmt, __mod);
     return _VSTD::copy(__nb, __ne, __s);
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_put<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_put<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_put<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_put<wchar_t>;
 #endif
 
 template <class _CharT, class _OutputIterator = ostreambuf_iterator<_CharT> >
 class _LIBCPP_TEMPLATE_VIS time_put_byname
     : public time_put<_CharT, _OutputIterator>
 {
 public:
     _LIBCPP_INLINE_VISIBILITY
     explicit time_put_byname(const char* __nm, size_t __refs = 0)
         : time_put<_CharT, _OutputIterator>(__nm, __refs) {}
 
     _LIBCPP_INLINE_VISIBILITY
     explicit time_put_byname(const string& __nm, size_t __refs = 0)
         : time_put<_CharT, _OutputIterator>(__nm, __refs) {}
 
 protected:
     _LIBCPP_INLINE_VISIBILITY
     ~time_put_byname() {}
 };
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_put_byname<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_put_byname<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_put_byname<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS time_put_byname<wchar_t>;
 #endif
 
 // money_base
 
 class _LIBCPP_TYPE_VIS money_base
 {
 public:
     enum part {none, space, symbol, sign, value};

 template <class _CharT, bool _International>
 locale::id
 moneypunct<_CharT, _International>::id;
 
 template <class _CharT, bool _International>
 const bool
 moneypunct<_CharT, _International>::intl;
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct<char, false>)
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct<char, true>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct<char, false>;
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct<char, true>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct<wchar_t, false>)
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct<wchar_t, true>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct<wchar_t, false>;
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct<wchar_t, true>;
 #endif
 
 // moneypunct_byname
 
 template <class _CharT, bool _International = false>
 class _LIBCPP_TEMPLATE_VIS moneypunct_byname
     : public moneypunct<_CharT, _International>
 {
private:
     pattern     __pos_format_;
     pattern     __neg_format_;
 
     void init(const char*);
 };
 
 template<> _LIBCPP_FUNC_VIS void moneypunct_byname<char, false>::init(const char*);
 template<> _LIBCPP_FUNC_VIS void moneypunct_byname<char, true>::init(const char*);
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct_byname<char, false>)
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct_byname<char, true>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct_byname<char, false>;
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct_byname<char, true>;
 
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
 template<> _LIBCPP_FUNC_VIS void moneypunct_byname<wchar_t, false>::init(const char*);
 template<> _LIBCPP_FUNC_VIS void moneypunct_byname<wchar_t, true>::init(const char*);
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct_byname<wchar_t, false>)
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct_byname<wchar_t, true>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct_byname<wchar_t, false>;
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS moneypunct_byname<wchar_t, true>;
 #endif
 
 // money_get
 
 template <class _CharT>
 class __money_get
 {
 protected:
else
         __dp = __mp.decimal_point();
         __ts = __mp.thousands_sep();
         __grp = __mp.grouping();
         __sym = __mp.curr_symbol();
         __fd = __mp.frac_digits();
     }
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __money_get<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __money_get<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __money_get<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __money_get<wchar_t>;
 #endif
 
 template <class _CharT, class _InputIterator = istreambuf_iterator<_CharT> >
 class _LIBCPP_TEMPLATE_VIS money_get
     : public locale::facet,
       private __money_get<_CharT>
 {
 public:
if (__do_get(__b, __e, __intl, __loc, __iob.flags(), __err, __neg, __ct,
                 break;
         __v.append(__w, __wn);
     }
     if (__b == __e)
         __err |= ios_base::eofbit;
     return __b;
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS money_get<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS money_get<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS money_get<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS money_get<wchar_t>;
 #endif
 
 // money_put
 
 template <class _CharT>
 class __money_put
 {
 protected:
if (__sn.size() > 1)
         __me = _VSTD::copy(__sn.begin()+1, __sn.end(), __me);
     // set alignment
     if ((__flags & ios_base::adjustfield) == ios_base::left)
         __mi = __me;
     else if ((__flags & ios_base::adjustfield) != ios_base::internal)
         __mi = __mb;
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __money_put<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __money_put<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __money_put<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS __money_put<wchar_t>;
 #endif
 
 template <class _CharT, class _OutputIterator = ostreambuf_iterator<_CharT> >
 class _LIBCPP_TEMPLATE_VIS money_put
     : public locale::facet,
       private __money_put<_CharT>
 {
 public:
money_put<_CharT, _OutputIterator>::do_put(iter_type __s, bool __intl,
     char_type* __mi;
     char_type* __me;
     this->__format(__mb, __mi, __me, __iob.flags(),
                    __digits.data(), __digits.data() + __digits.size(), __ct,
                    __neg, __pat, __dp, __ts, __grp, __sym, __sn, __fd);
     return __pad_and_output(__s, __mb, __mi, __me, __iob, __fl);
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS money_put<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS money_put<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS money_put<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS money_put<wchar_t>;
 #endif
 
 // messages
 
 class _LIBCPP_TYPE_VIS messages_base
 {
 public:
     typedef ptrdiff_t catalog;
if (__c != -1)
         __c <<= 1;
     nl_catd __cat = (nl_catd)__c;
     catclose(__cat);
 #else // !_LIBCPP_HAS_CATOPEN
     (void)__c;
 #endif // _LIBCPP_HAS_CATOPEN
 }
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS messages<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS messages<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS messages<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS messages<wchar_t>;
 #endif
 
 template <class _CharT>
 class _LIBCPP_TEMPLATE_VIS messages_byname
     : public messages<_CharT>
 {
 public:
     typedef messages_base::catalog catalog;
     typedef basic_string<_CharT> string_type;
 
     _LIBCPP_INLINE_VISIBILITY
     explicit messages_byname(const char*, size_t __refs = 0)
         : messages<_CharT>(__refs) {}
 
     _LIBCPP_INLINE_VISIBILITY
     explicit messages_byname(const string&, size_t __refs = 0)
         : messages<_CharT>(__refs) {}
 
 protected:
     _LIBCPP_INLINE_VISIBILITY
     ~messages_byname() {}
 };
 
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS messages_byname<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS messages_byname<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE_EVEN_IN_DEBUG_MODE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS messages_byname<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS messages_byname<wchar_t>;
 #endif
 
 template<class _Codecvt, class _Elem = wchar_t,
          class _Wide_alloc = allocator<_Elem>,
          class _Byte_alloc = allocator<char> >
 class _LIBCPP_TEMPLATE_VIS wstring_convert
 {
 public:

libcxx/include/ostream

 basic_ostream<_CharT, _Traits>&
 operator<<(basic_ostream<_CharT, _Traits>& __os, const bitset<_Size>& __x)
 {
     return __os << __x.template to_string<_CharT, _Traits>
                         (use_facet<ctype<_CharT> >(__os.getloc()).widen('0'),
                          use_facet<ctype<_CharT> >(__os.getloc()).widen('1'));
 }
 
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ostream<char>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ostream<char>;
 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ostream<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ostream<wchar_t>;
 #endif
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP_OSTREAM

libcxx/include/sstream

 void
 swap(basic_stringstream<_CharT, _Traits, _Allocator>& __x,
      basic_stringstream<_CharT, _Traits, _Allocator>& __y)
 {
     __x.swap(__y);
 }
 
 #if defined(_LIBCPP_ABI_ENABLE_ADDITIONAL_IOSTREAM_EXPLICIT_INSTANTIATIONS_1)
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_stringbuf<char>)
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_stringstream<char>)
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ostringstream<char>)
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_istringstream<char>)
+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>;
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_istringstream<char>;
 #endif
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP_SSTREAM

libcxx/include/streambuf

 
 template <class _CharT, class _Traits>
 typename basic_streambuf<_CharT, _Traits>::int_type
 basic_streambuf<_CharT, _Traits>::overflow(int_type)
 {
     return traits_type::eof();
 }
 
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_streambuf<char>)
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_streambuf<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_streambuf<char>;
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_streambuf<wchar_t>;
 
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ios<char>)
-_LIBCPP_EXTERN_TEMPLATE(class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ios<wchar_t>)
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ios<char>;
+extern template class _LIBCPP_EXTERN_TEMPLATE_TYPE_VIS basic_ios<wchar_t>;
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP_STREAMBUF

libcxx/include/string

 basic_string<_CharT, _Traits, _Allocator>
 operator+(const basic_string<_CharT, _Traits, _Allocator>& __x, const _CharT* __y);
 
 template<class _CharT, class _Traits, class _Allocator>
 _LIBCPP_CONSTEXPR_AFTER_CXX17
 basic_string<_CharT, _Traits, _Allocator>
 operator+(const basic_string<_CharT, _Traits, _Allocator>& __x, _CharT __y);
 
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS string operator+<char, char_traits<char>, allocator<char> >(char const*, string const&))
+extern template _LIBCPP_FUNC_VIS string operator+<char, char_traits<char>, allocator<char> >(char const*, string const&);
 
 template <class _Iter>
 struct __string_is_trivial_iterator : public false_type {};
 
 template <class _Tp>
 struct __string_is_trivial_iterator<_Tp*>
     : public is_arithmetic<_Tp> {};
 
#endif
     friend _LIBCPP_CONSTEXPR_AFTER_CXX17 basic_string operator+<>(const value_type*, const basic_string&);
     friend _LIBCPP_CONSTEXPR_AFTER_CXX17 basic_string operator+<>(value_type, const basic_string&);
     friend _LIBCPP_CONSTEXPR_AFTER_CXX17 basic_string operator+<>(const basic_string&, const value_type*);
     friend _LIBCPP_CONSTEXPR_AFTER_CXX17 basic_string operator+<>(const basic_string&, value_type);
 };
 
 // These declarations must appear before any functions are implicitly used
 // so that they have the correct visibility specifier.
+#define _LIBCPP_DECLARE(...) extern template __VA_ARGS__;
 #ifdef _LIBCPP_ABI_STRING_OPTIMIZED_EXTERNAL_INSTANTIATION
-    _LIBCPP_STRING_UNSTABLE_EXTERN_TEMPLATE_LIST(_LIBCPP_EXTERN_TEMPLATE, char)
+    _LIBCPP_STRING_UNSTABLE_EXTERN_TEMPLATE_LIST(_LIBCPP_DECLARE, char)
 #   ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-        _LIBCPP_STRING_UNSTABLE_EXTERN_TEMPLATE_LIST(_LIBCPP_EXTERN_TEMPLATE, wchar_t)
+        _LIBCPP_STRING_UNSTABLE_EXTERN_TEMPLATE_LIST(_LIBCPP_DECLARE, wchar_t)
 #   endif
 #else
-    _LIBCPP_STRING_V1_EXTERN_TEMPLATE_LIST(_LIBCPP_EXTERN_TEMPLATE, char)
+    _LIBCPP_STRING_V1_EXTERN_TEMPLATE_LIST(_LIBCPP_DECLARE, char)
 #   ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
-        _LIBCPP_STRING_V1_EXTERN_TEMPLATE_LIST(_LIBCPP_EXTERN_TEMPLATE, wchar_t)
+        _LIBCPP_STRING_V1_EXTERN_TEMPLATE_LIST(_LIBCPP_DECLARE, wchar_t)
 #   endif
 #endif
+#undef _LIBCPP_DECLARE
 
 
 #if _LIBCPP_STD_VER >= 17
 template<class _InputIterator,
          class _CharT = __iter_value_type<_InputIterator>,
          class _Allocator = allocator<_CharT>,
          class = enable_if_t<__is_cpp17_input_iterator<_InputIterator>::value>,
          class = enable_if_t<__is_allocator<_Allocator>::value>

libcxx/include/valarray

private:
     valarray& __assign_range(const value_type* __f, const value_type* __l);
 };
 
 #if _LIBCPP_STD_VER > 14
 template<class _Tp, size_t _Size>
 valarray(const _Tp(&)[_Size], size_t) -> valarray<_Tp>;
 #endif
 
-_LIBCPP_EXTERN_TEMPLATE(_LIBCPP_FUNC_VIS void valarray<size_t>::resize(size_t, size_t))
+extern template _LIBCPP_FUNC_VIS void valarray<size_t>::resize(size_t, size_t);
 
 template <class _Op, class _Tp>
 struct _UnaryOp<_Op, valarray<_Tp> >
 {
     typedef typename _Op::__result_type __result_type;
     typedef typename decay<__result_type>::type value_type;
 
     _Op __op_;

libcxxabi/CMakeLists.txt

 if (LIBCXXABI_HAS_EXTERNAL_THREAD_API)
   add_definitions(-D_LIBCPP_HAS_THREAD_API_EXTERNAL)
 endif()
 
 if (LIBCXXABI_BUILD_EXTERNAL_THREAD_LIBRARY)
   add_definitions(-D_LIBCPP_HAS_THREAD_LIBRARY_EXTERNAL)
 endif()
 
-# Prevent libc++abi from having library dependencies on libc++
-add_definitions(-D_LIBCPP_DISABLE_EXTERN_TEMPLATE)
-
 if (MSVC)
   add_definitions(-D_CRT_SECURE_NO_WARNINGS)
 endif()
 
 if (LIBCXXABI_SILENT_TERMINATE)
   add_definitions(-DLIBCXXABI_SILENT_TERMINATE)
 endif()