[libc++][NFC] Add missing license headers

Also standardize the license comment in several files where it was
different from what we normally do.

[libc++] Mark slow tests as unsupported on GCC

Some tests in our test suite are unbelievably slow on GCC due to the
use of the always_inline attribute. See [1] for more details.

This patch introduc

[libc++] Mark slow tests as unsupported on GCC

Some tests in our test suite are unbelievably slow on GCC due to the
use of the always_inline attribute. See [1] for more details.

This patch introduces the GCC-ALWAYS_INLINE-FIXME lit feature to
disable tests that are plagued by that issue. At the same time, it
moves several existing tests from ad-hoc `UNSUPPORTED: gcc-12` markup
to the new GCC-ALWAYS_INLINE-FIXME feature, and marks the slowest tests
reported by the CI as `UNSUPPORTED: GCC-ALWAYS_INLINE-FIXME`.

[1]: https://discourse.llvm.org/t/rfc-stop-supporting-extern-instantiations-with-gcc/71277/1

Differential Revision: https://reviews.llvm.org/D152736

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[libc++][format] Removes the experimental status.

The code has been quite ready for a while now and there are no more ABI
breaking papers. So this is a good time to mark the feature as stable.

Revi

[libc++][format] Removes the experimental status.

The code has been quite ready for a while now and there are no more ABI
breaking papers. So this is a good time to mark the feature as stable.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D150802

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[libc++][format] Implements LWG3892.

This LWG issue is based on the discussion regarding

P2733R3 Fix handling of empty specifiers in std::format

This paper was disussed and changed a few times i

[libc++][format] Implements LWG3892.

This LWG issue is based on the discussion regarding

P2733R3 Fix handling of empty specifiers in std::format

This paper was disussed and changed a few times in LEWG during the
Issaquah meeting. The paper was not voted in, instead LEWG asked for
a DR against C++26.

This LWG issue contains the direction voted by LEWG. This issue has not
been voted in yet. However it fixes some of the defencies on the
container based formatting. Without this fix the range-default-formatter
for strings looks bad when used in containers.

The changes of this issue match the intended changes of P27333.

type fmt before after (if changed)
---------------------------------------------------------------
char {} a
char {:?} 'a'
array<char, 1> {} ['a']
array<char, 1> {::} [a]
array<char, 1> {::c} [a]
array<char, 1> {::?} ['a']
map<char, char> {} {a: a} -> {'a': 'a'}
map<char, char> {::} {'a': 'a'}
set<char> {} {'a'}
set<char> {::} {a}
set<char> {::c} {a}
set<char> {::?} {'a'}
tuple<char> {} ('a')
stack<char> {} ['a']
stack<char> {::} [a]
stack<char> {::c} [a]
stack<char> {::?} ['a']
array<array<char, 1>, 1> {} [[a]] -> {'a': 'a'}
array<array<char, 1>, 1> {::} [['a']]
array<array<char, 1>, 1> {:::} [[a]]
array<array<char, 1>, 1> {:::c} [[a]]
array<array<char, 1>, 1> {:::?} [['a']]
array<tuple<char>, 1> {} [(a)] -> [('a')]
tuple<tuple<char>> {} ((a)) -> (('a'))
tuple<array<char, 1>> {} ([a]) -> (['a'])

Note the optimization text as mentioned in the tuple formatter can't be
done. The call to parse may affect the formatter so its state needs to
be preserved.

Reviewed By: ldionne, #libc, EricWF

Differential Revision: https://reviews.llvm.org/D145847

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[libc++] Use named Lit features to flag back-deployment XFAILs

Instead of writing something like `XFAIL: use_system_cxx_lib && target=...`
to XFAIL back-deployment tests, introduce named Lit feature

[libc++] Use named Lit features to flag back-deployment XFAILs

Instead of writing something like `XFAIL: use_system_cxx_lib && target=...`
to XFAIL back-deployment tests, introduce named Lit features like
`availability-shared_mutex-missing` to represent those. This makes the
XFAIL annotations leaner, and solves the problem of XFAIL comments
potentially getting out of sync. This would also make it easier for
another vendor to add their own annotations to the test suite by simply
changing how the feature is defined for their OS releases, instead
of having to modify hundreds of tests to add repetitive annotations.

This doesn't touch *all* annotations -- only annotations that were widely
duplicated are given named features (e.g. when filesystem or shared_mutex
were introduced). I still think it probably doesn't make sense to have a
named feature for every single fix we make to the dylib.

This is in essence a revert of 2659663, but since then the test suite
has changed significantly. Back when I did 2659663, the configuration
files we have for the test suite right now were being bootstrapped and
it wasn't clear how to provide these features for back-deployment in
that context. Since then, we have a streamlined way of defining these
features in `features.py` and that doesn't impact the ability for a
configuration file to stay minimal.

The original motivation for this change was that I am about to propose
a change that would touch essentially all XFAIL annotations for back-deployment
in the test suite, and this greatly reduces the number of lines changed
by that upcoming change, in addition to making the test suite generally
better.

Differential Revision: https://reviews.llvm.org/D146359

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[libc++] Remove availability markup for std::format

std::format is currently experimental, so there is technically no
deployment target requirement for it (since the only symbols required
for it are

[libc++] Remove availability markup for std::format

std::format is currently experimental, so there is technically no
deployment target requirement for it (since the only symbols required
for it are in `libc++experimental.a`).

However, some parts of std::format depend indirectly on the floating
point std::to_chars implementation, which does have deployment target
requirements.

This patch removes all the availability format for std::format and
updates the XFAILs in the tests to properly explain why they fail
on old deployment targets, when they do. It also changes a couple
of tests to avoid depending on floating-point std::to_chars when
it isn't fundamental to the test.

Finally, some tests are marked as XFAIL but I added a comment saying

TODO FMT This test should not require std::to_chars(floating-point)

These tests do not fundamentally depend on floating-point std::to_chars,
however they end up failing because calling std::format even without a
floating-point argument to format will end up requiring floating-point
std::to_chars. I believe this is an implementation artifact that could
be avoided in all cases where we know the format string at compile-time.
In the tests, I added the TODO comment only to the places where we could
do better and actually avoid relying on floating-point std::to_chars
because we know the format string at compile-time.

Differential Revision: https://reviews.llvm.org/D134598

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[libc++][test] Adds more generic test macros.

These macros are intended to replace the macros in rapid-cxx-test.h.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D1428

[libc++][test] Adds more generic test macros.

These macros are intended to replace the macros in rapid-cxx-test.h.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D142808

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[libc++][format] Implements range_formatter

Implements parts of
- P2286R8 Formatting Ranges
- P2585R0 Improving default container formatting

Depends on D140651

Reviewed By: ldionne, #libc

Differe

[libc++][format] Implements range_formatter

Implements parts of
- P2286R8 Formatting Ranges
- P2585R0 Improving default container formatting

Depends on D140651

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D140653

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[libc++][format] Adds new test macros.

These macros make it easier to log additional information. This is
useful for formatting tests. It also properly disables additional
information when locales a

[libc++][format] Adds new test macros.

These macros make it easier to log additional information. This is
useful for formatting tests. It also properly disables additional
information when locales are disabled in libc++.

Reviewed By: #libc, ldionne

Differential Revision: https://reviews.llvm.org/D140651

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[libc++][format] Adds formatter for tuple and pair

Implements parts of
- P2286R8 Formatting Ranges

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D136775