<filesystem> is a C++17 addition. In C++11 and C++14 modes, we actually
have all the code for <filesystem> but it is hidden behind a non-inline
namespace __fs so it is not accessible. Instead of doing this unusual
dance, just guard the code for filesystem behind a classic C++17 check
like we normally do.
Since LIBCXX_ENABLE_FILESYSTEM now truly represents whether the
platform supports a filesystem (as opposed to whether the <filesystem>
library is provided), we can provide a few additional classes from
the <filesystem> library even when the platform does not have support
for a filesystem. For example, this allows performing path manipulations
using std::filesystem::path even on platforms where there is no actual
filesystem.
rdar://107061236
Differential Revision: https://reviews.llvm.org/D152382
Since those features are general properties of the environment, it makes
sense to use them from libc++abi too, and so the name libcpp-has-no-xxx
doesn't make sense.
Differential Revision: https://reviews.llvm.org/D126482
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
It was added in commit 0b71bf793924301d53cf01eeb0a27e96fea17791, "[libcxx] [test] Add a test for conversions between wchar_t, utf8, char16_t, char32_t and windows native narrow code pages"
