Some embedded platforms do not wish to support the C library functionality
for handling wchar_t because they have no use for it. It makes sense for
libc++ to work properly on those platforms, so this commit adds a carve-out
of functionality for wchar_t.
Unfortunately, unlike some other carve-outs (e.g. random device), this
patch touches several parts of the library. However, despite the wide
impact of this patch, I still think it is important to support this
configuration since it makes it much simpler to port libc++ to some
embedded platforms.
Differential Revision: https://reviews.llvm.org/D111265
fdc41e11f was reverted in e46c1def5 because it broke the C++11 build.
We shouldn't be using enable_if_t in C++11, instead we must use
enable_if<...>::type.
This reverts commit fdc41e11f9. It causes the
libcxx/modules/stds_include.sh.cpp test to fail with:
libcxx/include/ostream:1039:45: error: no template named 'enable_if_t'; did you mean 'enable_if'?
template <class _Stream, class _Tp, class = enable_if_t<
Still investigating what's causing this and reverting in the meantime to get
the bots green again.
Libc++ had an issue where nonsensical code like
decltype(std::stringstream{} << std::vector<int>{});
would compile, as long as you kept the expression inside decltype in
an unevaluated operand. This turned out to be that we didn't implement
LWG1203, which clarifies what we should do in that case.
rdar://58769296
Louis Dionne