[libc++][C++03] Use `__cxx03/` headers in C++03 mode (#109002)

This patch implements the forwarding to frozen C++03 headers as
discussed in
https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-

[libc++][C++03] Use `__cxx03/` headers in C++03 mode (#109002)

This patch implements the forwarding to frozen C++03 headers as
discussed in
https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc. In the
RFC, we initially proposed selecting the right headers from the Clang
driver, however consensus seemed to steer towards handling this in the
library itself. This patch implements that direction.

At a high level, the changes basically amount to making each public
header look like this:

```
// inside <vector>
#ifdef _LIBCPP_CXX03_LANG
# include <__cxx03/vector>
#else
// normal <vector> content
#endif
```

In most cases, public headers are simple umbrella headers so there isn't
much code in the #else branch. In other cases, the #else branch contains
the actual implementation of the header.

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[libc++] Add #if 0 block to all the top-level headers (#119234)

Including The frozen C++03 headers results in a lot of formatting
changes in the main headers, so this splits these changes into a
sep

[libc++] Add #if 0 block to all the top-level headers (#119234)

Including The frozen C++03 headers results in a lot of formatting
changes in the main headers, so this splits these changes into a
separate commit instead.

This is part of
https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc.

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[libc++][modules] Modularize <cstddef> (#107254)

Many headers include `<cstddef>` just for size_t, and pulling in
additional content (e.g. the traits used for std::byte) is unnecessary.
To solve t

[libc++][modules] Modularize <cstddef> (#107254)

Many headers include `<cstddef>` just for size_t, and pulling in
additional content (e.g. the traits used for std::byte) is unnecessary.
To solve this problem, this patch splits up `<cstddef>` into
subcomponents so that headers can include only the parts that they
actually require.

This has the added benefit of making the modules build a lot stricter
with respect to IWYU, and also providing a canonical location where we
define `std::size_t` and friends (which were previously defined in
multiple headers like `<cstddef>` and `<ctime>`).

After this patch, there's still many places in the codebase where we
include `<cstddef>` when `<__cstddef/size_t.h>` would be sufficient.
This patch focuses on removing `<cstddef>` includes from __type_traits
to make these headers non-circular with `<cstddef>`. Additional
refactorings can be tackled separately.

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[libc++][NFC] Minor reformatting in <cstddef>

[libc++] Remove _LIBCPP_DISABLE_NODISCARD_EXTENSIONS and refactor the tests (#87094)

This also adds a few tests that were missing.

[libc++] Clean up includes of <__assert> (#80091)

Originally, we used __libcpp_verbose_abort to handle assertion failures.
That function was declared from all public headers. Since we don't use
th

[libc++] Clean up includes of <__assert> (#80091)

Originally, we used __libcpp_verbose_abort to handle assertion failures.
That function was declared from all public headers. Since we don't use
that mechanism anymore, we don't need to declare __libcpp_verbose_abort
from all public headers, and we can clean up a lot of unnecessary
includes.

This patch also moves the definition of the various assertion categories
to the <__assert> header, since we now rely on regular IWYU for these
assertion macros.

rdar://105510916

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[libc++] Format the code base (#74334)

This patch runs clang-format on all of libcxx/include and libcxx/src, in
accordance with the RFC discussed at [1]. Follow-up patches will format
the benchmar

[libc++] Format the code base (#74334)

This patch runs clang-format on all of libcxx/include and libcxx/src, in
accordance with the RFC discussed at [1]. Follow-up patches will format
the benchmarks, the test suite and remaining parts of the code. I'm
splitting this one into its own patch so the diff is a bit easier to
review.

This patch was generated with:

find libcxx/include libcxx/src -type f \
| grep -v 'module.modulemap.in' \
| grep -v 'CMakeLists.txt' \
| grep -v 'README.txt' \
| grep -v 'libcxx.imp' \
| grep -v '__config_site.in' \
| xargs clang-format -i

A Git merge driver is available in libcxx/utils/clang-format-merge-driver.sh
to help resolve merge and rebase issues across these formatting changes.

[1]: https://discourse.llvm.org/t/rfc-clang-formatting-all-of-libc-once-and-for-all

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[libc++][NFC] Add a few explicit 'inline' keywords, mostly in <chrono> (#75234)

Even though constexpr implicitly makes functions inline, we try not to
rely on this implicit effect in the code base.

[libc++][NFC] Add a few explicit 'inline' keywords, mostly in <chrono> (#75234)

Even though constexpr implicitly makes functions inline, we try not to
rely on this implicit effect in the code base. We are mostly consistent
about using `inline` on non-template free-functions to make it clear
that we don't have an ODR violation.

This patch simply fixes a few places where we didn't explicitly use
inline on non-template free functions, presumably because they were
constexpr.

Fixes #75227

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[libc++][NFC] Refactor __enable_ifs in <cstddef> to be defaulted
template arguments

This makes the library more consistent and reduces the size of mangled
names a bit as a bonus.

[libc++][NFC] Replace _LIBCPP_STD_VER > x with _LIBCPP_STD_VER >= x

This change is almost fully mechanical. The only interesting change is in `generate_feature_test_macro_components.py` to generate

[libc++][NFC] Replace _LIBCPP_STD_VER > x with _LIBCPP_STD_VER >= x

This change is almost fully mechanical. The only interesting change is in `generate_feature_test_macro_components.py` to generate `_LIBCPP_STD_VER >=` instead. To avoid churn in the git-blame this commit should be added to the `.git-blame-ignore-revs` once committed.

Reviewed By: ldionne, var-const, #libc

Spies: jloser, libcxx-commits, arichardson, arphaman, wenlei

Differential Revision: https://reviews.llvm.org/D143962

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[libc++] Diagnose when header search paths are set up incorrectly

An issue I often see in codebases compiled for unusual platforms is
that header search paths are specified manually and are subtly w

[libc++] Diagnose when header search paths are set up incorrectly

An issue I often see in codebases compiled for unusual platforms is
that header search paths are specified manually and are subtly wrong.
For example, people will manually add `-isystem <some-toolchain>/usr/include`,
which ends up messing up the layering of header search paths required by
libc++ (because the C Standard Library now appears *before* libc++ in
the search paths). Without this patch, this will end up causing
compilation errors that are pretty inscrutable. This patch aims to
improve the user experience by diagnosing this issue explicitly.

In all cases I can think of, I would expect that a compilation error
occur if these header search paths are not layered properly. This
should only provide an explicit diagnostic instead of failing due
to seemingly unrelated compilation errors.

Differential Revision: https://reviews.llvm.org/D131441

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[libc++] Add a bunch of missing _LIBCPP_HIDE_FROM_ABI

Reviewed By: ldionne, Mordante, var-const, huixie90, #libc

Spies: jloser, libcxx-commits, arichardson, miyuki

Differential Revision: https://r

[libc++] Add a bunch of missing _LIBCPP_HIDE_FROM_ABI

Reviewed By: ldionne, Mordante, var-const, huixie90, #libc

Spies: jloser, libcxx-commits, arichardson, miyuki

Differential Revision: https://reviews.llvm.org/D129968

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[libc++] Use __enable_if_t and is_integral in cstddef

Reviewed By: ldionne, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D126469

[libc++] Granularize parts of <type_traits>

`<type_traits>` is quite a large header, so I'll granularize it in a few steps.

Reviewed By: ldionne, #libc

Spies: libcxx-commits, mgorny

Differential

[libc++] Granularize parts of <type_traits>

`<type_traits>` is quite a large header, so I'll granularize it in a few steps.

Reviewed By: ldionne, #libc

Spies: libcxx-commits, mgorny

Differential Revision: https://reviews.llvm.org/D124755

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[libc++] Ensure that all public C++ headers include <__assert>

This patch changes the requirement for getting the declaration of the
assertion handler from including <__assert> to including any publ

[libc++] Ensure that all public C++ headers include <__assert>

This patch changes the requirement for getting the declaration of the
assertion handler from including <__assert> to including any public
C++ header of the library. Note that C compatibility headers are
excluded because we don't implement all the C headers ourselves --
some of them are taken straight from the C library, like assert.h.

It also adds a generated test to check it. Furthermore, this new
generated test is designed in a way that will make it possible to
replace almost all the existing test-generation scripts with this
system in upcoming patches.

Differential Revision: https://reviews.llvm.org/D122506

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[libc++] Remove the ability to use the std::nullptr_t emulation in C++03 mode

Back in https://reviews.llvm.org/D109459, we stopped using the C++03
emulation for std::nullptr_t by default, which was

[libc++] Remove the ability to use the std::nullptr_t emulation in C++03 mode

Back in https://reviews.llvm.org/D109459, we stopped using the C++03
emulation for std::nullptr_t by default, which was an ABI break. We
still left a knob for users to turn it back on if they were broken by
the change, with a note that we would remove that knob after one release.

The time has now come to remove the knob and clean up the std::nullptr_t
emulation.

Differential Revision: https://reviews.llvm.org/D114786

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[libc++] Normalize all our '#pragma GCC system_header', and regression-test.

Now we'll notice if a header forgets to include this magic phrase.

Differential Revision: https://reviews.llvm.org/D1188

[libc++] Normalize all our '#pragma GCC system_header', and regression-test.

Now we'll notice if a header forgets to include this magic phrase.

Differential Revision: https://reviews.llvm.org/D118800

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[libc++][NFC] Add namespace comments in ranges

With this patch there should be no more namespaces without closing comment

Reviewed By: ldionne, Quuxplusone, #libc

Spies: libcxx-commits

Differenti

[libc++][NFC] Add namespace comments in ranges

With this patch there should be no more namespaces without closing comment

Reviewed By: ldionne, Quuxplusone, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D118668

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[runtimes][NFC] Remove filenames at the top of the license notice

We've stopped doing it in libc++ for a while now because these names
would end up rotting as we move things around and copy/paste st

[runtimes][NFC] Remove filenames at the top of the license notice

We've stopped doing it in libc++ for a while now because these names
would end up rotting as we move things around and copy/paste stuff.
This cleans up all the existing files so as to stop the spreading
as people copy-paste headers around.

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[libc++] Add an option to disable wide character support in libc++

Some embedded platforms do not wish to support the C library functionality
for handling wchar_t because they have no use for it. It

[libc++] Add an option to disable wide character support in libc++

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

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[libc++][NFC] Remove #endif comments for really small conditionals on _LIBCPP_HAS_NO_UNICODE_CHARS

We generally don't put a comment on the #endif when the #if block is so small
that it's unambiguous

[libc++][NFC] Remove #endif comments for really small conditionals on _LIBCPP_HAS_NO_UNICODE_CHARS

We generally don't put a comment on the #endif when the #if block is so small
that it's unambiguous what the #endif refers to.

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[libc++] Use the using_if_exists attribute when provided

As discussed on cfe-dev [1], use the using_if_exists Clang attribute when
the compiler supports it. This makes it easier to port libc++ on to

[libc++] Use the using_if_exists attribute when provided

As discussed on cfe-dev [1], use the using_if_exists Clang attribute when
the compiler supports it. This makes it easier to port libc++ on top of
new platforms that don't fully support the C Standard library.

Previously, libc++ would fail to build when trying to import a missing
declaration in a <cXXXX> header. With the attribute, the declaration will
simply not be imported into namespace std, and hence it won't be available
for libc++ to use. In many cases, the declarations were *not* actually
required for libc++ to work (they were only surfaced for users to use
them as std::XXXX), so not importing them into namespace std is acceptable.

The same thing could be achieved by conscious usage of `#ifdef` along
with platform detection, however that quickly creates a maintenance
problem as libc++ is ported to new platforms. Furthermore, this problem
is exacerbated when mixed with vendor internal-only platforms, which can
lead to difficulties maintaining a downstream fork of the library.

For the time being, we only use the using_if_exists attribute when it
is supported. At some point in the future, we will start removing #ifdef
paths that are unnecessary when the attribute is supported, and folks
who need those #ifdef paths will be required to use a compiler that
supports the attribute.

[1]: http://lists.llvm.org/pipermail/cfe-dev/2020-June/066038.html

Differential Revision: https://reviews.llvm.org/D90257

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[libc++] s/_LIBCPP_NO_HAS_CHAR8_T/_LIBCPP_HAS_NO_CHAR8_T/g

This was raised in D94511.

Differential Revision: https://reviews.llvm.org/D100736

[libc++] NFC: Normalize `#endif //` comment indentation

[libc++] Implement D2351R0 "Mark all library static cast wrappers as [[nodiscard]]"

These [[nodiscard]] annotations are added as a conforming extension;
it's unclear whether the paper will actually

[libc++] Implement D2351R0 "Mark all library static cast wrappers as [[nodiscard]]"

These [[nodiscard]] annotations are added as a conforming extension;
it's unclear whether the paper will actually be adopted and make them
mandatory, but they do seem like good ideas regardless.

https://isocpp.org/files/papers/D2351R0.pdf

This patch implements the paper's effect on:
- std::to_integer, std::to_underlying
- std::forward, std::move, std::move_if_noexcept
- std::as_const
- std::identity

The paper also affects (but libc++ does not yet have an implementation of):
- std::bit_cast

Differential Revision: https://reviews.llvm.org/D99895

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