Currently, the library-internal feature test macros are only defined if
the feature is not available, and always have the prefix
`_LIBCPP_HAS_NO_`. This patch changes that, so that they are always
defined and have the prefix `_LIBCPP_HAS_` instead. This changes the
canonical use of these macros to `#if _LIBCPP_HAS_FEATURE`, which means
that using an undefined macro (e.g. due to a missing include) is
diagnosed now. While this is rather unlikely currently, a similar change
in `<__configuration/availability.h>` caught a few bugs. This also
improves readability, since it removes the double-negation of `#ifndef
_LIBCPP_HAS_NO_FEATURE`.
The current patch only touches the macros defined in `<__config>`. If
people are happy with this approach, I'll make a follow-up PR to also
change the macros defined in `<__config_site>`.
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
These function makes it easier to write generic unit tests for the
format header. It solves the issue where it's not possible to use
`templated_prefix"foo"`
where `templated_prefix` resolves to: nothing, `L`, `u8`, `u`,
or `U`. The templated_prefix would be more faster during execution.
Reviewed By: ldionne, #libc, curdeius
Differential Revision: https://reviews.llvm.org/D93414
