[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++] Avoid including <string> in <mutex> (#116254)

[libcxx] Fix inverted `has_terminal` condition

Summary:
This used to indicate "has no terminal" and now it indicates "has
terminal" but the check was not changed.

[libc++] Refactor the configuration macros to being always defined (#112094)

This is a follow-up to #89178. This updates the `<__config_site>`
macros.

[libcxx] Add `LIBCXX_HAS_TERMINAL_AVAILABLE` CMake option to disable `print` terminal checks (#99259)

Adds a new CMake option called `LIBCXX_HAS_TERMINAL_AVAILABLE` that
prevents us from checking f

[libcxx] Add `LIBCXX_HAS_TERMINAL_AVAILABLE` CMake option to disable `print` terminal checks (#99259)

Adds a new CMake option called `LIBCXX_HAS_TERMINAL_AVAILABLE` that
prevents us from checking for `isatty`.

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[libc++][NFC] Run clang-format on libcxx/include again (#95874)

As time went by, a few files have become mis-formatted w.r.t.
clang-format. This was made worse by the fact that formatting was not

[libc++][NFC] Run clang-format on libcxx/include again (#95874)

As time went by, a few files have become mis-formatted w.r.t.
clang-format. This was made worse by the fact that formatting was not
being enforced in extensionless headers. This commit simply brings all
of libcxx/include in-line with clang-format again.

We might have to do this from time to time as we update our clang-format
version, but frankly this is really low effort now that we've formatted
everything once.

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[libc++] Make the __availability header a sub-header of __config (#93083)

In essence, this header has always been related to configuration of
the library but we didn't want to put it inside <__conf

[libc++] Make the __availability header a sub-header of __config (#93083)

In essence, this header has always been related to configuration of
the library but we didn't want to put it inside <__config> due to
complexity reasons. Now that we have sub-headers in <__config>, we
can move <__availability> to it and stop including it everywhere since
we already obtain the required macros via <__config>.

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[libc++][format] P3142R0: Printing Blank Lines with `println` (#87277)

Implements https://wg21.link/P3142R0

Applied retroactively as DR, same as stdlibc++ and MS STL:

https://github.com/orgs/m

[libc++][format] P3142R0: Printing Blank Lines with `println` (#87277)

Implements https://wg21.link/P3142R0

Applied retroactively as DR, same as stdlibc++ and MS STL:

https://github.com/orgs/microsoft/projects/1143?pane=issue&itemId=57457187

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[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++][print] Moves is_terminal to the dylib. (#80464)

Having the test in the header requires including unistd.h on POSIX
platforms. This header has other declarations which may conflict with
co

[libc++][print] Moves is_terminal to the dylib. (#80464)

Having the test in the header requires including unistd.h on POSIX
platforms. This header has other declarations which may conflict with
code that uses named declarations provided by this header. For example
code using "int pipe;" would conflict with the function pipe in this
header.

Moving the code to the dylib means std::print would not be available on
Apple backdeployment targets. On POSIX platforms there is no transcoding
required so a not Standard conforming implementation is still a useful
and the observable differences are minimal. This behaviour has been done
for print before https://github.com/llvm/llvm-project/pull/76293.

Note questions have been raised in LWG4044 "Confusing requirements for
std::print on POSIX platforms", whether or not the isatty check on POSIX
platforms is required. When this LWG issue is resolved the
backdeployment targets could become Standard compliant.

This patch is intended to be backported to the LLVM-18 branch.

Fixes: https://github.com/llvm/llvm-project/issues/79782

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[libc++][print] Includes <format>. (#76333)

The overloads of `println` are specified in terms of `format`. The
function `format` is specified to work with ranges.

The implementations for `printl

[libc++][print] Includes <format>. (#76333)

The overloads of `println` are specified in terms of `format`. The
function `format` is specified to work with ranges.

The implementations for `println` do not include `<format>`, but
libc++'s granularized header. This means the following example does not
work

#include <vector>
#include <print>

int main() {
std::vector<int> v{1, 2, 3};
std::println("{}", v);
}

(The other print functions also require this to work, they are specified
in terms of other format functions.)

Fixes: https://github.com/llvm/llvm-project/issues/71925

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[libc++][print] Renames __use_unicode. (#76290)

This is addresses a review comment in #73262.

[libc++][hardening] Categorize more assertions. (#75918)

Also introduce `_LIBCPP_ASSERT_PEDANTIC` for assertions violating which
results in a no-op or other benign behavior, but which may neverthel

[libc++][hardening] Categorize more assertions. (#75918)

Also introduce `_LIBCPP_ASSERT_PEDANTIC` for assertions violating which
results in a no-op or other benign behavior, but which may nevertheless
indicate a bug in the invoking code.

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[libc++][print] Adds ostream overloads. (#73262)

Finishes implementation of
- P2093R14 Formatted output
- P2539R4 Should the output of std::print to a terminal be synchronized
with the underlying

[libc++][print] Adds ostream overloads. (#73262)

Finishes implementation of
- P2093R14 Formatted output
- P2539R4 Should the output of std::print to a terminal be synchronized
with the underlying stream?

Differential Revision: https://reviews.llvm.org/D156609

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[libc++][print] Adds stdout functions.

Implements parts of
- P2093R14 Formatted output
- P2539R4 Should the output of std::print to a terminal be
synchronized with the underlying stream?

[libc++][print] Adds stdout functions.

Implements parts of
- P2093R14 Formatted output
- P2539R4 Should the output of std::print to a terminal be
synchronized with the underlying stream?

Depends on D150044

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D155262

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[libc++][print] Adds FILE functions.

Drive-by fix to make sure the __retarget_buffer works correctly whan
using a hint of 1. This was discovered in one of the new tests.

Drive-by fixes __retarget_b

[libc++][print] Adds FILE functions.

Drive-by fix to make sure the __retarget_buffer works correctly whan
using a hint of 1. This was discovered in one of the new tests.

Drive-by fixes __retarget_buffer when initialized with size 1.

Implements parts of
- P2093R14 Formatted output
- P2539R4 Should the output of std::print to a terminal be
synchronized with the underlying stream?

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D150044

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[libc++][format] Adds a UTF transcoder.

This is a preparation for

P2093R14 Formatted output

When the output of print is to the terminal it needs to use the native
API. This means transcoding UTF

[libc++][format] Adds a UTF transcoder.

This is a preparation for

P2093R14 Formatted output

When the output of print is to the terminal it needs to use the native
API. This means transcoding UTF-8 to UTF-16 on Windows. The encoder's
interface is modeled after

P2728 Unicode in the Library, Part 1: UTF Transcoding

But only the required part for P2093R14 is implemented.

On Windows wchar_t is 16 bits, in order to test on platforms where
wchar_t is 32 bits the transcoder has support for char16_t. It also adds
and UTF-8 to UTF-32 encoder which is useful for other tests.

Note it is possible to use <codecvt> for transcoding, but that header is
deprecated. So rather write new code that is not deprecated; the hard
part, decoding, has already been done. The <codecvt> header also
requires locale support while the new code works without including
<locale>.

Note the current transcoder implementation can be optimized since it
basically does UTF-8 -> UTF-32 -> UTF-16. The first goal is to have a
working implementation. Since it's not part of the ABI it's possible to
do the optimization later.

Depends on D149672

Reviewed By: ldionne, tahonermann, #libc

Differential Revision: https://reviews.llvm.org/D150031

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