[libc++] Allow enabling assertions when back-deploying

When back-deploying to older platforms, we can still provide assertions,
but we might not be able to provide a great implementation for the ver

[libc++] Allow enabling assertions when back-deploying

When back-deploying to older platforms, we can still provide assertions,
but we might not be able to provide a great implementation for the verbose
handler. Instead, we can just call ::abort().

Differential Revision: https://reviews.llvm.org/D131199

(cherry picked from commit e36f9e13bca41223bd6af7e49bf020e58a676e9d)

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[libc++] Rename __libcpp_assertion_handler to __libcpp_verbose_abort

With the goal of reusing that handler to do other things besides
handling assertions (such as terminating when an exception is th

[libc++] Rename __libcpp_assertion_handler to __libcpp_verbose_abort

With the goal of reusing that handler to do other things besides
handling assertions (such as terminating when an exception is thrown
under -fno-exceptions), the name `__libcpp_assertion_handler` doesn't
really make sense anymore.

Furthermore, I didn't want to use the name `__libcpp_abort_handler`,
since that would give the impression that the handler is called
whenever `std::abort()` is called, which is not the case at all.

Differential Revision: https://reviews.llvm.org/D130562

(cherry picked from commit 507125af3d0b953cb56bce2e5b8000249fe1ef53)

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[libc++] Removes _LIBCPP_AVAILABILITY_TO_CHARS.

After moving the std::to_chars base 10 implementation from the dylib to
the header the integral overloads of std::to_chars are available on all
platfo

[libc++] Removes _LIBCPP_AVAILABILITY_TO_CHARS.

After moving the std::to_chars base 10 implementation from the dylib to
the header the integral overloads of std::to_chars are available on all
platforms.

Remove the _LIBCPP_AVAILABILITY_TO_CHARS availability macro and update
the tests.

Depends on D125704

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D125745

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[libc++] Add a lightweight overridable assertion handler

This patch adds a lightweight assertion handler mechanism that can be
overriden at link-time in a fashion similar to `operator new`.

This is

[libc++] Add a lightweight overridable assertion handler

This patch adds a lightweight assertion handler mechanism that can be
overriden at link-time in a fashion similar to `operator new`.

This is a third take on https://llvm.org/D121123 (which allowed customizing
the assertion handler at compile-time), and https://llvm.org/D119969
(which allowed customizing the assertion handler at runtime only).

This approach is, I think, the best of all three explored approaches.
Indeed, replacing the assertion handler in user code is ergonomic,
yet we retain the ability to provide a custom assertion handler when
deploying to older platforms that don't have a default handler in
the dylib.

As-is, this patch provides a pretty good amount of backwards compatibility
with the previous debug mode:

- Code that used to set _LIBCPP_DEBUG=0 in order to get basic assertions
in their code will still get basic assertions out of the box, but
those assertions will be using the new assertion handler support.
- Code that was previously compiled with references to __libcpp_debug_function
and friends will work out-of-the-box, no changes required. This is
because we provide the same symbols in the dylib as we used to.
- Code that used to set a custom __libcpp_debug_function will stop
compiling, because we don't provide that declaration anymore. Users
will have to migrate to the new way of setting a custom assertion
handler, which is extremely easy. I suspect that pool of users is
very limited, so breaking them at compile-time is probably acceptable.

The main downside of this approach is that code being compiled with
assertions enabled but deploying to an older platform where the assertion
handler didn't exist yet will fail to compile. However users can easily
fix the problem by providing a custom assertion handler and defining
the _LIBCPP_AVAILABILITY_CUSTOM_ASSERTION_HANDLER_PROVIDED macro to
let the library know about the custom handler. In a way, this is
actually a feature because it avoids a load-time error that one would
otherwise get when trying to run the code on the older target.

Differential Revision: https://reviews.llvm.org/D121478

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[libc++][NFC] Change availability macro from macosx to macos

The Clang documentation mentions that macosx is supported for backwards
compatibility, but it's deprecated.

[libc++][NFC] Slight improvement to __availability documentation

[libc++] Fix incorrect availability markup for bad_optional_access & friends

In 7fb40e1569d, I changed the availability for bad_optional_access and
friends from macOS 10.14 to 10.13 after conducting

[libc++] Fix incorrect availability markup for bad_optional_access & friends

In 7fb40e1569d, I changed the availability for bad_optional_access and
friends from macOS 10.14 to 10.13 after conducting an investigation on
old dylibs. It turns out that macOS 10.13 did have bad_optional_access,
however the dylib on iOS didn't match the dylib on macOS, so those
exception classes were only introduced in iOS 12.

Thanks to Aditya Kumar for noticing this.

Differential Revision: https://reviews.llvm.org/D121735

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[libc++][NFC] Remove redundant comment about availability of std::format

[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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Microsoft's floating-point to_chars powered by Ryu and Ryu Printf

Microsoft would like to contribute its implementation of floating-point to_chars to libc++. This uses the impossibly fast Ryu and Ry

Microsoft's floating-point to_chars powered by Ryu and Ryu Printf

Microsoft would like to contribute its implementation of floating-point to_chars to libc++. This uses the impossibly fast Ryu and Ryu Printf algorithms invented by Ulf Adams at Google. Upstream repos: https://github.com/microsoft/STL and https://github.com/ulfjack/ryu .

Licensing notes: MSVC's STL is available under the Apache License v2.0 with LLVM Exception, intentionally chosen to match libc++. We've used Ryu under the Boost Software License.

This patch contains minor changes from Jorg Brown at Google, to adapt the code to libc++. He verified that it works in Google's Linux-based environment, but then I applied more changes on top of his, so any compiler errors are my fault. (I haven't tried to build and test libc++ yet.) Please tell me if we need to do anything else in order to follow https://llvm.org/docs/DeveloperPolicy.html#attribution-of-changes .

Notes:

* libc++'s integer charconv is unchanged (except for a small refactoring). MSVC's integer charconv hasn't been tuned for performance yet, so you're not missing anything.
* Floating-point from_chars isn't part of this patch because Jorg found that MSVC's implementation (derived from our CRT's strtod) was slower than Abseil's. If you're unable to use Abseil or another implementation due to licensing or technical considerations, Microsoft would be delighted if you used MSVC's from_chars (and you can just take it, or ask us to provide a patch like this). Ulf is also working on a novel algorithm for from_chars.
* This assumes that float is IEEE 32-bit, double is IEEE 64-bit, and long double is also IEEE 64-bit.
* I have added MSVC's charconv tests (the whole thing: integer/floating from_chars/to_chars), but haven't adapted them to libcxx's harness at all. (These tests will be available in the microsoft/STL repo soon.)
* Jorg added int128 codepaths. These were originally present in upstream Ryu, and I removed them from microsoft/STL purely for performance reasons (MSVC doesn't support int128; Clang on Windows does, but I found that x64 intrinsics were slightly faster).
* The implementation is split into 3 headers. In MSVC's STL, charconv contains only Microsoft-written code. xcharconv_ryu.h contains code derived from Ryu (with significant modifications and additions). xcharconv_ryu_tables.h contains Ryu's large lookup tables (they were sufficiently large to make editing inconvenient, hence the separate file). The xmeow.h convention is MSVC's for internal headers; you may wish to rename them.
* You should consider separately compiling the lookup tables (see https://github.com/microsoft/STL/issues/172 ) for compiler throughput and reduced object file size.
* See https://github.com/StephanTLavavej/llvm-project/commits/charconv for fine-grained history. (If necessary, I can perform some rebase surgery to show you what Jorg changed relative to the microsoft/STL repo; currently that's all fused into the first commit.)

Differential Revision: https://reviews.llvm.org/D70631

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Revert "Microsoft's floating-point to_chars powered by Ryu and Ryu Printf"

This reverts commit a8025e06fc0f2fe1bbee9e1a6f15c336bfbdcb05 since
it triggers PR52584 with debug info enabled.

Microsoft's floating-point to_chars powered by Ryu and Ryu Printf

Microsoft would like to contribute its implementation of floating-point to_chars to libc++. This uses the impossibly fast Ryu and Ry

Microsoft's floating-point to_chars powered by Ryu and Ryu Printf

Microsoft would like to contribute its implementation of floating-point to_chars to libc++. This uses the impossibly fast Ryu and Ryu Printf algorithms invented by Ulf Adams at Google. Upstream repos: https://github.com/microsoft/STL and https://github.com/ulfjack/ryu .

Licensing notes: MSVC's STL is available under the Apache License v2.0 with LLVM Exception, intentionally chosen to match libc++. We've used Ryu under the Boost Software License.

This patch contains minor changes from Jorg Brown at Google, to adapt the code to libc++. He verified that it works in Google's Linux-based environment, but then I applied more changes on top of his, so any compiler errors are my fault. (I haven't tried to build and test libc++ yet.) Please tell me if we need to do anything else in order to follow https://llvm.org/docs/DeveloperPolicy.html#attribution-of-changes .

Notes:

* libc++'s integer charconv is unchanged (except for a small refactoring). MSVC's integer charconv hasn't been tuned for performance yet, so you're not missing anything.
* Floating-point from_chars isn't part of this patch because Jorg found that MSVC's implementation (derived from our CRT's strtod) was slower than Abseil's. If you're unable to use Abseil or another implementation due to licensing or technical considerations, Microsoft would be delighted if you used MSVC's from_chars (and you can just take it, or ask us to provide a patch like this). Ulf is also working on a novel algorithm for from_chars.
* This assumes that float is IEEE 32-bit, double is IEEE 64-bit, and long double is also IEEE 64-bit.
* I have added MSVC's charconv tests (the whole thing: integer/floating from_chars/to_chars), but haven't adapted them to libcxx's harness at all. (These tests will be available in the microsoft/STL repo soon.)
* Jorg added int128 codepaths. These were originally present in upstream Ryu, and I removed them from microsoft/STL purely for performance reasons (MSVC doesn't support int128; Clang on Windows does, but I found that x64 intrinsics were slightly faster).
* The implementation is split into 3 headers. In MSVC's STL, charconv contains only Microsoft-written code. xcharconv_ryu.h contains code derived from Ryu (with significant modifications and additions). xcharconv_ryu_tables.h contains Ryu's large lookup tables (they were sufficiently large to make editing inconvenient, hence the separate file). The xmeow.h convention is MSVC's for internal headers; you may wish to rename them.
* You should consider separately compiling the lookup tables (see https://github.com/microsoft/STL/issues/172 ) for compiler throughput and reduced object file size.
* See https://github.com/StephanTLavavej/llvm-project/commits/charconv for fine-grained history. (If necessary, I can perform some rebase surgery to show you what Jorg changed relative to the microsoft/STL repo; currently that's all fused into the first commit.)

Differential Revision: https://reviews.llvm.org/D70631

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[libc++][format] Add __format_arg_store.

This implements the struct `__format_arg_store` and its dependencies:
* the class basic_format_arg,
* the class basic_format_args,
* the class basic_format_c

[libc++][format] Add __format_arg_store.

This implements the struct `__format_arg_store` and its dependencies:
* the class basic_format_arg,
* the class basic_format_args,
* the class basic_format_context,
* the function make_format_args,
* the function wmake_format_args,
* the function visit_format_arg,
* several Standard required typedefs.

The following parts will be implemented in a later patch:

* the child class `basic_format_arg::handle`,
* the function `basic_format_arg::basic_format_arg(const T* p)`.

The following extension has been implemented:
* the class basic_format_arg supports `__[u]int128_t` on platform where libc++ supports 128 bit integrals.

Implements parts of:
* P0645 Text Formatting

Completes:
* LWG3371 visit_format_arg and make_format_args are not hidden friends
* LWG3542 basic_format_arg mishandles basic_string_view with custom traits

Note https://mordante.github.io/blog/2021/06/05/format.html gives a bit more information about the goals and non-goals of this initial patch series.

Reviewed By: #libc, ldionne, vitaut

Differential Revision: https://reviews.llvm.org/D103357

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[libc++] Enable the synchronization library on Apple platforms

The synchronization library was marked as disabled on Apple platforms
up to now because we were not 100% sure that it was going to be A

[libc++] Enable the synchronization library on Apple platforms

The synchronization library was marked as disabled on Apple platforms
up to now because we were not 100% sure that it was going to be ABI
stable. However, it's been some time since we shipped it in upstream
libc++ now and there's been no changes so far. This patch enables the
synchronization library on Apple platforms, and hence commits the ABI
stability as far as that vendor is concerned.

Differential Revision: https://reviews.llvm.org/D96790

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[libc++][format] Adds availability macros for std::format.

This prevents std::format to be available until there's an ABI stable
version. (This only impacts the Apple platform.)

Depends on D102703

[libc++][format] Adds availability macros for std::format.

This prevents std::format to be available until there's an ABI stable
version. (This only impacts the Apple platform.)

Depends on D102703

Reviewed By: ldionne, #libc

Differential Revision: https://reviews.llvm.org/D102705

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

[libc++] Make feature-test macros consistent with availability macros

Before this patch, feature-test macros didn't take special availability
markup into account, which means that feature-test macro

[libc++] Make feature-test macros consistent with availability macros

Before this patch, feature-test macros didn't take special availability
markup into account, which means that feature-test macros can sometimes
appear to "lie". For example, if you compile in C++20 mode and target
macOS 10.13, the __cpp_lib_filesystem feature-test macro will be provided
even though the <filesystem> declarations are marked as unavailable.
This patch fixes that.

rdar://68142369

Differential Revision: https://reviews.llvm.org/D94983

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[libc++] Rework the whole availability markup implementation

Currently, vendor-specific availability markup is enabled by default.
This means that even when building against trunk libc++, the header

[libc++] Rework the whole availability markup implementation

Currently, vendor-specific availability markup is enabled by default.
This means that even when building against trunk libc++, the headers
will by default prevent you from using some features that were not
released in the dylib on your target platform. This is a source of
frustration since people building libc++ from sources are usually not
trying to use some vendor's released dylib.

For that reason, I've been thinking for a long time that availability
annotations should be off by default, which is the primary change that
this commit enables.

In addition, it reworks the implementation to make it easier for new
vendors to add availability annotations for their platform, and it
refreshes the documentation to reflect the current state of the codebase.

Finally, a CMake configuration option is added to control whether
availability annotations should be turned on for the flavor of libc++
being created. The intent is for vendors like Apple to turn it on, and
for the upstream libc++ to leave it off (the default).

Differential Revision: https://reviews.llvm.org/D90843

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