[libc++] Implement std::not_fn<NTTP> (#86133)

Implement `std::not_fn<NTTP>` from "P2714R1 Bind front and back to NTTP callables".

[libc++][NFC] Merge is{,_nothrow,_trivially}{,_copy,_move,_default}{_assignable,_constructible} (#85308)

These headers have become very small by using compiler builtins, often
containing only two d

[libc++][NFC] Merge is{,_nothrow,_trivially}{,_copy,_move,_default}{_assignable,_constructible} (#85308)

These headers have become very small by using compiler builtins, often
containing only two declarations. This merges these headers, since
there doesn't seem to be much of a benefit keeping them separate.

Specifically, `is_{,_nothrow,_trivially}{assignable,constructible}` are
kept and the `copy`, `move` and `default` versions of these type traits
are moved in to the respective headers.

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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++] Replace uses of _VSTD:: by std:: (#74331)

As part of the upcoming clang-formatting of libc++, this patch performs
the long desired removal of the _VSTD macro.

See https://discourse.llvm

[libc++] Replace uses of _VSTD:: by std:: (#74331)

As part of the upcoming clang-formatting of libc++, this patch performs
the long desired removal of the _VSTD macro.

See https://discourse.llvm.org/t/rfc-clang-formatting-all-of-libc-once-and-for-all
for the clang-format proposal.

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[libc++][Modules] Add missing includes and exports

Several headers are missing includes for things they use.

type_traits.is_enum needs to export type_traits.integral_constant so that clients can ac

[libc++][Modules] Add missing includes and exports

Several headers are missing includes for things they use.

type_traits.is_enum needs to export type_traits.integral_constant so that clients can access its `value` member without explicitly including __type_traits/integral_constant.h themselves.

Make `subrange_fwd` a peer submodule to `subrange` rather than a submodule of it, and have `subrange` export `subrange_fwd`. That will make it easier to programmatically generate modules for the private detail headers, and it will accomplish the same effect that __ranges/subrange.h will make subrange_kind visible.

Reviewed By: Mordante, #libc

Differential Revision: https://reviews.llvm.org/D150055

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[libc++] Granularize <type_traits> includes

Reviewed By: ldionne, #libc, #libc_abi

Spies: #libc_vendors, smeenai, libcxx-commits

Differential Revision: https://reviews.llvm.org/D145320

[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++][NFC] Rename the constexpr macros

This was discussed on Discord with the consensus that we should rename the macros.

Reviewed By: ldionne, Mordante, var-const, avogelsgesang, jloser, #libc

[libc++][NFC] Rename the constexpr macros

This was discussed on Discord with the consensus that we should rename the macros.

Reviewed By: ldionne, Mordante, var-const, avogelsgesang, jloser, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D131498

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[libc++] Revert "Protect users from relying on detail headers" & related changes

This commit reverts 5aaefa51 (and also partly 7f285f48e77 and b6d75682f9,
which were related to the original commit).

[libc++] Revert "Protect users from relying on detail headers" & related changes

This commit reverts 5aaefa51 (and also partly 7f285f48e77 and b6d75682f9,
which were related to the original commit). As landed, 5aaefa51 had
unintended consequences on some downstream bots and didn't have proper
coverage upstream due to a few subtle things. Implementing this is
something we should do in libc++, however we'll first need to address
a few issues listed in https://reviews.llvm.org/D106124#3349710.

Differential Revision: https://reviews.llvm.org/D120683

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[libcxx][modules] protects users from relying on detail headers

libc++ has started splicing standard library headers into much more
fine-grained content for maintainability. It's very likely that ou

[libcxx][modules] protects users from relying on detail headers

libc++ has started splicing standard library headers into much more
fine-grained content for maintainability. It's very likely that outdated
and naive tooling (some of which is outside of LLVM's scope) will
suggest users include things such as <__ranges/access.h> instead of
<ranges>, and Hyrum's law suggests that users will eventually begin to
rely on this without the help of tooling. As such, this commit
intends to protect users from themselves, by making it a hard error for
anyone outside of the standard library to include libc++ detail headers.

Differential Revision: https://reviews.llvm.org/D106124

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[libc++] Replace includes of <utility> with specific detail headers

Basically a rebase of D104980; most of that patch had already happened
via gradual drive-by changes, but this finishes it up.
Don'

[libc++] Replace includes of <utility> with specific detail headers

Basically a rebase of D104980; most of that patch had already happened
via gradual drive-by changes, but this finishes it up.
Don't touch the inclusions from `<__functional_base>`, `<__hash_table>`,
or `<__locale>`; those could be removed if we propagated the
inclusions up to the includers of those files, but there are lots
of those includers.

`<algorithm>`, `<functional>`, and `<memory>` already include `<utility>`
at the top level. `<iterator>` did not, so I've added it there.

Differential Revision: https://reviews.llvm.org/D119020

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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++] Alphabetize header #includes. NFCI.

The NFC part of D116809. We still want to enforce this in CI,
but the mechanism for that is still to-be-determined.

Differential Revision: https://revie

[libc++] Alphabetize header #includes. NFCI.

The NFC part of D116809. We still want to enforce this in CI,
but the mechanism for that is still to-be-determined.

Differential Revision: https://reviews.llvm.org/D116809

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[libc++] Use enable_if_t instead of _EnableIf

I just ran into a compiler error involving __bind_back and some overloads
that were being disabled with _EnableIf. I noticed that the error message
was

[libc++] Use enable_if_t instead of _EnableIf

I just ran into a compiler error involving __bind_back and some overloads
that were being disabled with _EnableIf. I noticed that the error message
was quite bad and did not mention the reason for the overload being
excluded. Specifically, the error looked like this:

candidate template ignored: substitution failure [with _Args =
<ContiguousView>]: no member named '_EnableIfImpl' in 'std::_MetaBase<false>'

Instead, when using enable_if or enable_if_t, the compiler is clever and
can produce better diagnostics, like so:

candidate template ignored: requirement 'is_invocable_v<
std::__bind_back_op<1, std::integer_sequence<unsigned long, 0>>,
std::ranges::views::__transform::__fn &, std::tuple<PlusOne> &,
ContiguousView>' was not satisfied [with _Args = <ContiguousView>]

Basically, it tries to do a poor man's implementation of concepts, which
is already a lot better than simply complaining about substitution failure.

Hence, this commit uses enable_if_t instead of _EnableIf whenever
possible. That is both more straightforward than using the internal
helper, and also leads to better error messages in those cases.

I understand the motivation for _EnableIf's implementation was to improve
compile-time performance, however I believe striving to improve error
messages is even more important for our QOI, hence this patch. Furthermore,
it is unclear that _EnableIf actually improved compile-time performance
in any noticeable way (see discussion in the review for details).

Differential Revision: https://reviews.llvm.org/D108216

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[libc++] Refactor __perfect_forward, bind_front and not_fn

This patch fixes the constrains on the __perfect_forward constructor
and its call operators, which were incorrect. In particular, it makes

[libc++] Refactor __perfect_forward, bind_front and not_fn

This patch fixes the constrains on the __perfect_forward constructor
and its call operators, which were incorrect. In particular, it makes
sure that we closely follow [func.require], which basically says that
we must deliver the bound arguments with the appropriate value category
or make the call ill-formed, but not silently fall back to using a
different value category.

As a fly-by, this patch also:
- Adds types __bind_front_t and __not_fn_t to make the result of
calling bind_front and not_fn more opaque, and improve diagnostics
for users.
- Adds a bunch of tests for bind_front and remove some that are now
redundant.
- Adds some missing _LIBCPP_HIDE_FROM_ABI annotations.

Immense thanks to @tcanens for raising awareness about this issue, and
providing help with the = delete bits.

Differential Revision: https://reviews.llvm.org/D107199

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[libcxx][functional][modular] splices <functional> into modular headers

Differential Revision: https://reviews.llvm.org/D104942