This does not include `std::compare_*_fallback`; those are coming later.
There's still an open question of how to implement std::strong_order
for `long double`, which has 80 value bits and 48 padding bits on x86-64,
and which is presumably *not* IEEE 754-compliant on PPC64 and so on.
So that part is left unimplemented.
Differential Revision: https://reviews.llvm.org/D110738
Actually there's one functional change here, which is that users can
no longer depend on <random> to include all of C++20 <concepts>. That
inclusion is so new that we believe nobody should be depending on it
yet, even in the presence of Hyrum's Law. We keep the includes of <vector>,
<algorithm>, etc., so as not to break pre-C++20 Hyrum's Law users.
Differential Revision: https://reviews.llvm.org/D114281
This is not mandated by the standard, so it goes in libcxx/test/libcxx/.
It's certainly arguable that the algorithms changed here
(`is_heap`, `is_sorted`, `min`, `max`) are harmless and we should
just let them copy their comparators once. But at the same time,
it's nice to have all our algorithms be 100% consistent and never
copy a comparator, not even once.
Differential Revision: https://reviews.llvm.org/D114136
We would have been defining it in <utility> instead of <charconv>. For
the time being, this doesn't change anything since we don't implement
the feature test macro anyways.
Also, as a fly-by, this removes obsolete feature test macro tests. There
was a brief time back in the days when we wrote feature test macro tests
manually. In particular, we had test files for __cpp_lib_to_chars and
__cpp_lib_memory_resource. Since we now have a principled way of generating
these tests with scripts, this commit removes the obsolete (and empty)
tests for these two feature test macros.
Differential Revision: https://reviews.llvm.org/D114243
std::atomic is, for the most part, just a thin veneer on top of compiler
builtins. Hence, it should be available even when threads are not available
on the system, and in fact there has been requests for such support.
This patch:
- Moves __libcpp_thread_poll_with_backoff to its own header so it can
be used in <atomic> when threads are disabled.
- Adds a dummy backoff policy for atomic polling that doesn't know about
threads.
- Adjusts the <atomic> feature-test macros so they are provided even when
threads are disabled.
- Runs the <atomic> tests when threads are disabled.
rdar://77873569
Differential Revision: https://reviews.llvm.org/D114109
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.
- Replace irrelevant synopsis by a comment
- Use a .verify.cpp test instead of .compile.fail.cpp
- Remove unnecessary includes in one of the tests (was a copy-paste error)
Differential Revision: https://reviews.llvm.org/D114094
This effort is dedicated to deflake the tests of the users which depend
on the unspecified behavior of algorithms and containers. This also
might help updating the sorting algorithm in libcxx which has the
quadratic worst case in the future or at least create a new one under
flag.
For detailed design, please see the design doc I provide in the patch.
Differential Revision: https://reviews.llvm.org/D96946
However, whether applications rely on the std::bad_function_call vtable
being in the dylib is still controlled by the ABI macro, since changing
that would be an ABI break.
Also separate preprocessor definitions for whether to use a key function
and whether to use a `bad_function_call`-specific `what` message
(`what` message is mandated by [LWG2233](http://wg21.link/LWG2233)).
Differential Revision: https://reviews.llvm.org/D92397
The return type of the deleted functions doesn't match the synopsis in
the standard.
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D114000
Places `format_to_n_result` to its own file. While working on D112361 it
turns out the type will be used outside the format header.
Reviewed By: #libc, Quuxplusone, Mordante
Differential Revision: https://reviews.llvm.org/D113831
This patch fixes the warnings which shows up when libcxx library started to be compiled in 32-bit mode on z/OS.
More specifically, the assignment from unsigned int to time_t aka long was flags as follows:
```
libcxx/include/c++/v1/__support/ibm/nanosleep.h:31:11: warning: implicit conversion changes signedness: 'unsigned int' to 'time_t' (aka 'long') [-Wsign-conversion]
__sec = sleep(static_cast<unsigned int>(__sec));
~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
libcxx/include/c++/v1/__support/ibm/nanosleep.h:36:36: warning: implicit conversion changes signedness: 'unsigned int' to 'long' [-Wsign-conversion]
__rem->tv_nsec = __micro_sec * 1000;
~ ~~~~~~~~~~~~^~~~~~
libcxx/include/c++/v1/__support/ibm/nanosleep.h:47:36: warning: implicit conversion changes signedness: 'unsigned int' to 'long' [-Wsign-conversion]
__rem->tv_nsec = __micro_sec * 1000;
~ ~~~~~~~~~~~~^~~~~~
3 warnings generated.
```
Here is a small test case illustrating the issue:
```
typedef long time_t ;
unsigned int sleep(unsigned int );
int main() {
time_t sec = 0;
#ifdef FIX
sec = static_cast<time_t>(sleep(static_cast<unsigned int>(sec)));
#else
sec = sleep(static_cast<unsigned int>(sec));
#endif
}
```
clang++ -c -Wsign-conversion -m32 t.C
```
t.C:8:9: warning: implicit conversion changes signedness: 'unsigned int' to 'time_t' (aka 'long') [-Wsign-conversion]
sec = sleep(static_cast<unsigned int>(sec));
~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Reviewed By: ldionne, #libc, Quuxplusone, Mordante
Differential Revision: https://reviews.llvm.org/D112837
Since coroutine is merged in C++ standard and the support for coroutine
seems relatively stable. It's the time to move the implementation of
coroutine out of the experimental directory and the std::experimental
namespace. This patch creates header <coroutine> with conformed
implementation with C++ standard. To avoid breaking user's code too
fast, the <experimental/coroutine> header is remained. Note that
<experimental/coroutine> is deprecated and it would be removed in
LLVM15.
Reviewed By: Quuxplusone, ldionne
Differential Revision: https://reviews.llvm.org/D109433
The template std::is_assignable<T, U> checks that T is assignable from
U. Hence, the order of operands in the instantiation of
std::is_assignable in the std::reverse_iterator::operator= condition
should be reversed.
This issue remained unnoticed because std::reverse_iterator has an
implicit conversion constructor. This patch adds a test to check that
the assignment operator is used directly, without any implicit
conversions. The patch also adds a similar test for
std::move_iterator.
Reviewed By: Quuxplusone, ldionne, #libc
Differential Revision: https://reviews.llvm.org/D113417
Right now we drop the char_traits template argument, which presumes that
string<_CharT, _Traits> and string<_CharT> are interchangeable.
Reviewed By: Mordante, #libc, Quuxplusone
Differential Revision: https://reviews.llvm.org/D112017
This addresses the usage of `operator&` in `<list>`.
(Note there are still more headers with the same issue.)
Reviewed By: #libc, Quuxplusone, ldionne
Differential Revision: https://reviews.llvm.org/D112654
This addresses the usage of `operator&` in `<forward_list>`.
(Note there are still more headers with the same issue.)
Reviewed By: #libc, Quuxplusone, ldionne
Differential Revision: https://reviews.llvm.org/D112660
Using user-provided data as a format string is a well known source of
security vulnerabilities. For this reason, it is a good idea to compile
our code with -Wformat-nonliteral, which basically warns if a non-constant
string is used as a format specifier. This is the compiler’s best signal
that a format string call may be insecure.
I audited the code after adding the warning and made sure that the few
places where we used a non-literal string as a format string were not
potential security issues. I either disabled the warning locally for
those instances or fixed the warning by using a literal. The idea is
that after we add the warning to the build, any new use of a non-literal
string in a format string will trigger a diagnostic, and we can either
get rid of it or disable the warning locally, which is a way of
acknowledging that it has been audited.
I also looked into enabling it in the test suite, which would perhaps
allow finding additional instances of it in our headers, however that
is not possible at the moment because Clang doesn't support putting
__attribute__((__format__(...))) on variadic templates, which would
be needed.
rdar://84571685
Differential Revision: https://reviews.llvm.org/D112927
Deduction guides for containers should not participate in overload
resolution when called with certain incorrect types (e.g. when called
with a template argument in place of an `InputIterator` that doesn't
qualify as an input iterator). Similarly, class template argument
deduction should not select `unique_ptr` constructors that take a
a pointer.
The tests try out every possible incorrect parameter (but never more
than one incorrect parameter in the same invocation).
Also add deduction guides to the synopsis for associative and unordered
containers (this was accidentally omitted from [D112510](https://reviews.llvm.org/D112510)).
Differential Revision: https://reviews.llvm.org/D112904
`__vector_base` exists for historical reasons and cannot be eliminated
entirely without breaking the ABI. Member variables are left
untouched -- this patch only does changes that clearly cannot affect the
ABI.
Differential Revision: https://reviews.llvm.org/D112976
However, whether applications rely on the std::bad_function_call vtable
being in the dylib is still controlled by the ABI macro, since changing
that would be an ABI break.
Differential Revision: https://reviews.llvm.org/D92397
Before this patch, `try_acquire` blocks instead of returning false.
This is because `__libcpp_thread_poll_with_backoff` interprets zero
as meaning infinite, causing `try_acquire` to wait indefinitely.
Thanks to Pablo Busse (pabusse) for the patch!
Differential Revision: https://reviews.llvm.org/D98334
These can't be made constexpr-constructible (constinit'able),
so they aren't C++20-conforming. Also, the platform versions are
going to be bigger than the atomic/futex version, so we'd have
the awkward situation that `semaphore<42>` could be bigger than
`semaphore<43>`, and that's just silly.
Differential Revision: https://reviews.llvm.org/D110110
These are not standard methods, neither libstdc++ nor MSVC STL provide
them.
In practice, one of them was untested and the other one was only used in
one single test.
Differential Revision: https://reviews.llvm.org/D113027
I was going to make a change in that area of the code and I noticed that
we basically duplicated the same code 5 times to handle integral types
and floating point types. This commit simply pulls the duplication into
a function.
Differential Revision: https://reviews.llvm.org/D112830
Since we no longer officially support Clang 11 remove the work-arounds
for this version.
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D112727
Some types that inherit from `view_interface` do not meet the
preconditions. This came up during discussion
in https://reviews.llvm.org/D112631. Currently, the behavior is IFNDR,
but the preconditions can be easily checked, so let's do so.
In particular, we know each public member function calls the
`__derived()` private function, so we can do the check there. We
intentionally do it as a `static_assert` instead of a `requires` clause
to avoid hard erroring in some cases, such as with incomplete types. An
example hard error is:
```
llvm-project/build/include/c++/v1/__ranges/view_interface.h:48:14: note: because 'sizeof(_Tp)' would be invalid: invalid application of 'sizeof' to an incomplete type 'MoveOnlyForwardRange'
requires { sizeof(_Tp); } &&
^
llvm-project/build/include/c++/v1/__ranges/view_interface.h:73:26: error: no matching member function for call to '__derived'
return ranges::begin(__derived()) == ranges::end(__derived());
^~~~~~~~~
llvm-project/libcxx/test/std/ranges/range.utility/view.interface/view.interface.pass.cpp:187:31: note: in instantiation of function template specialization 'std::ranges::view_interface<MoveOnlyForwardRange>::empty<Mov
eOnlyForwardRange>' requested here
assert(!std::move(moveOnly).empty());
```
Reviewed By: Quuxplusone, Mordante, #libc
Differential Revision: https://reviews.llvm.org/D112665
`is_error_condition_enum_v` and `is_error_code_enum_v` are currently of
type `size_t`, but the standard mandates they are of type `bool`.
This is an ABI break technically since the size of these variable
templates has changed. Document it as such in the release notes.
Fixes https://bugs.llvm.org/show_bug.cgi?id=50755
Reviewed By: ldionne, Quuxplusone, #libc, var-const
Differential Revision: https://reviews.llvm.org/D112553
Add deduction guides to `valarray` and `scoped_allocator_adaptor`. This largely
finishes implementation of the paper:
* deduction guides for other classes mentioned in the paper were
implemented previously (see the list below);
* deduction guides for several classes contained in the proposal
(`reference_wrapper`, `lock_guard`, `scoped_lock`, `unique_lock`,
`shared_lock`) were removed by [LWG2981](https://wg21.link/LWG2981).
Also add deduction guides to the synopsis for the few classes (e.g. `pair`)
where they were missing.
The only part of the paper that isn't fully implemented after this patch is
making sure certain deduction guides don't participate in overload resolution
when given incorrect template parameters.
List of significant commits implementing the other parts of P0433 (omitting some
minor fixes):
* [pair](af65856eec)
* [basic_string](6d9f750dec)
* [array](0ca8c0895c)
* [deque](dbb6f8a817)
* [forward_list](e076700b77)
* [list](4a227e582b)
* [vector](df8f754792)
* [queue/stack/priority_queue](5b8b8b5dce)
* [basic_regex](edd5e29cfe)
* [optional](f35b4bc395)
* [map/multimap](edfe8525de)
* [set/multiset](e20865c387)
* [unordered_set/unordered_multiset](296a80102a)
* [unordered_map/unordered_multimap](dfcd4384cb)
* [function](e1eabcdfad)
* [tuple](1308011e1b)
* [shared_ptr/weak_ptr](83564056d4)
Additional notes:
* It was revision 2 of the paper that was voted into the Standard.
P0433R3 is a separate paper that is not part of the Standard.
* The paper also mandates removing several `make_*_searcher` functions
(e.g. `make_boyer_moore_searcher`) which are currently not implemented
(except in `experimental/`).
* The `__cpp_lib_deduction_guides` feature test macro from the paper was
accidentally omitted from the Standard.
Differential Revision: https://reviews.llvm.org/D112510
This is going to be necessary to implement some range adaptors.
As a fly-by fix, rename _LIBCPP_INLINE_VISIBILITY to _LIBCPP_HIDE_FROM_ABI
and remove a redundant inline keyword.
Differential Revision: https://reviews.llvm.org/D112650
Mark LWG2731 as complete. The type alias `mutex_type` is only provided if
`scoped_lock` is given one mutex type and it has been implemented that
way since the beginning of Clang 5 it seems. There already are tests for
verifying existence (and lack thereof) for `mutex_type` type alias
depending on the number of mutex types, so there is nothing to
do for this LWG issue.
Reviewed By: Quuxplusone, Mordante, #libc
Differential Revision: https://reviews.llvm.org/D112462
This patch refactors the shared_ptr methods from being defined out-of-line
to being defined inline in the class, like what we do for all new code in
the library. The benefits of doing that are that code is not as scattered
around and is hence easier to understand, and it avoids a ton of duplication
due to SFINAE checks. Defining the method where it is declared also removes
the possibility for mismatched attributes.
As a fly-by change, this also:
- Adds a few _LIBCPP_HIDE_FROM_ABI attributes
- Uses __enable_if_t instead of enable_if as a function argument, to match
the style that we use everywhere else.
Differential Revision: https://reviews.llvm.org/D112478
Several parts in the `chrono` synopsis for C++20 are not yet
implemented. The current recommendation is that things are added to the
synopsis when implemented -- not beforehand. As such, remove the
not-yet-implemented parts to avoid confusion.
Reviewed By: ldionne, Quuxplusone, #libc
Differential Revision: https://reviews.llvm.org/D111922
Also fix a few places in the `shared_ptr` implementation where
`element_type` was passed to the `__is_compatible` helper. This could
result in `remove_extent` being applied twice to the pointer's template
type (first by the definition of `element_type` and then by the helper),
potentially leading to somewhat less readable error messages for some
incorrect code.
Differential Revision: https://reviews.llvm.org/D112092
Based on the comment of @Quuxplusone in D111961. It seems no tests are
affected, but give it a run on the CI to be sure.
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D112231
This addresses the usage of `operator&` in `<vector>`.
I now added tests for the current offending cases. I wonder whether it
would be better to add one addressof test per directory and test all
possible violations. Also to guard against possible future errors?
(Note there are still more headers with the same issue.)
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D111961
According to the standard [vector.capacity]/5, std::vector<T>::reserve
shall throw an exception of type std::length_error when the requested
capacity exceeds max_size().
This behavior is not implemented correctly: the function 'reserve'
simply propagates the exception from allocator<T>::allocate. Before
D110846 that exception used to be of type std::length_error (which is
correct for vector<T>::reserve, but incorrect for
allocator<T>::allocate).
This patch fixes the issue and adds regression tests.
Reviewed By: Quuxplusone, ldionne, #libc
Differential Revision: https://reviews.llvm.org/D112068
std::vector<bool> rebinds the supplied allocator to construct objects
of type '__storage_type' rather than 'bool'. Allocators are allowed to
use explicit conversion constructors, so care must be taken when
performing conversions.
Reviewed By: ldionne, #libc
Differential Revision: https://reviews.llvm.org/D112150
The path functions in this patch are unimplemented (as per the TODO comment from upstream). To avoid running into a linker error (missing symbol), this patch raises a compile error by commenting out the functions, which is more user friendly.
Differential Revision: https://reviews.llvm.org/D111892
`weekday` has a static member function `__weekday_from_days` which is
not part of the mandated public interface of `weeekday` according to the
standard. Since it is only used internally in the constructors of
`weekday`, let's make it private.
Reviewed By: ldionne, Mordante, #libc
Differential Revision: https://reviews.llvm.org/D112072
Currently the member functions std::allocator<T>::allocate,
std::experimental::pmr::polymorphic_allocator::allocate and
std::resource_adaptor<T>::do_allocate throw an exception of type
std::length_error when the requested size exceeds the maximum size.
According to the C++ standard ([allocator.members]/4,
[mem.poly.allocator.mem]/1), std::allocator<T>::allocate and
std::pmr::polymorphic_allocator::allocate must throw a
std::bad_array_new_length exception in this case.
The patch fixes the issue with std::allocator<T>::allocate and changes
the type the exception thrown by
std::experimental::pmr::resource_adaptor<T>::do_allocate to
std::bad_array_new_length as well for consistency.
The patch resolves LWG 3237, LWG 3038 and LWG 3190.
Reviewed By: ldionne, #libc, Quuxplusone
Differential Revision: https://reviews.llvm.org/D110846
Implement LWG3480 which enables `directory_iterator` and
`recursive_directory_iterator` to be both a `borrowed_range` and a
`view`.
Reviewed By: ldionne, #libc
Differential Revision: https://reviews.llvm.org/D111644
Mark LWG3274 as complete. The feature test macro `__cpp_lib_span` was added in
`6d2599e4f776d0cd88438cb82a00c4fc25cc3f67`.
https://wg21.link/p1024 mentions marking `span:::empty()` with
`[[nodiscard]]` which is not done yet. So, do that and add tests.
Reviewed By: ldionne, Quuxplusone, Mordante, #libc
Differential Revision: https://reviews.llvm.org/D111516
Fixes the tests added in D110852 for the debug iterators.
Similar issues with hijacking `operator&` still exist, they will be
addressed separately.
Reviewed By: #libc, ldionne, Quuxplusone
Differential Revision: https://reviews.llvm.org/D111564
While looking at LWG-2988 and P0558 it seems the issues were already
implemented, but the synopsis wasn't updated. Some of the tests didn't
validate the `noexcept` status. A few tests were missing completely:
- `atomic_wait_explicit`
- `atomic_notify_one`
- `atomic_notify_all`
Mark P0558 as complete, didn't investigate which version of libc++ first
includes this. It seems the paper has been retroactively applied. I
couldn't find whether this is correct, but looking at cppreference it
seems intended.
Completes
- LWG-2988 Clause 32 cleanup missed one typename
- P0558 Resolving atomic<T> named base class inconsistencies
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D103765
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
Implement P2401 which adds a `noexcept` specification to
`std::exchange`. Treated as a defect fix which is the motivation for
applying this change to all standards mode rather than just C++23 or
later as the paper suggests.
Reviewed By: Quuxplusone, Mordante, #libc
Differential Revision: https://reviews.llvm.org/D111481
There is an empty `namespace std` in `type_traits` which was originally
used when `std::byte` was added in
c97d8aa866. At some point, the bitwise operators
on `std::byte` got relocated but this empty namespace was left around.
Remove it.
Reviewed By: Quuxplusone, Mordante, #libc
Differential Revision: https://reviews.llvm.org/D111512
Implement parts of P1614, including three-way comparison for tuples, and expand testing.
Reviewed By: ldionne, Mordante, #libc
Differential Revision: https://reviews.llvm.org/D108250
While looking at the review comments in D103765 there was an oddity in
the tests for the following functions:
- atomic_fetch_add
- atomic_fetch_add_explicit
- atomic_fetch_sub
- atomic_fetch_sub_explicit
Libc++ allows usage of
`atomic_fetch_add<int>(atomic<int*>*, atomic<int*>::difference_type);`
MSVC and GCC reject this code: https://godbolt.org/z/9d8WzohbE
This makes the atomic `fetch(add|sub).*` Standard conforming and removes the non-conforming extensions.
Fixes PR47908
Reviewed By: ldionne, #libc
Differential Revision: https://reviews.llvm.org/D103983
Replace `&__rhs` with `_VSTD::addressof(__rhs)` to guard against ADL hijacking
of `operator&` in `operator=`. Thanks to @CaseyCarter for bringing it to our
attention.
Similar issues with hijacking `operator&` still exist, they will be
addressed separately.
Reviewed By: #libc, Quuxplusone, ldionne
Differential Revision: https://reviews.llvm.org/D110852
Implements the formatter for Boolean types.
[format.formatter.spec]/2.3
For each charT, for each cv-unqualified arithmetic type ArithmeticT other
than char, wchar_t, char8_t, char16_t, or char32_t, a specialization
```
template<> struct formatter<ArithmeticT, charT>;
```
This removes the stub implemented in D96664.
Implements parts of:
- P0645 Text Formatting
- P1652 Printf corner cases in std::format
Completes:
- P1868 width: clarifying units of width and precision in std::format
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D103670
Implements the formatter for all fundamental integer types.
[format.formatter.spec]/2.1
The specializations
```
template<> struct formatter<char, char>;
template<> struct formatter<char, wchar_t>;
template<> struct formatter<wchar_t, wchar_t>;
```
This removes the stub implemented in D96664.
Implements parts of:
- P0645 Text Formatting
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D103466
Implements the formatter for all fundamental integer types
(except `char`, `wchar_t`, and `bool`).
[format.formatter.spec]/2.3
For each charT, for each cv-unqualified arithmetic type ArithmeticT other
than char, wchar_t, char8_t, char16_t, or char32_t, a specialization
```
template<> struct formatter<ArithmeticT, charT>;
```
This removes the stub implemented in D96664.
As an extension it adds partial support for 128-bit integer types.
Implements parts of:
- P0645 Text Formatting
- P1652 Printf corner cases in std::format
Completes:
- LWG-3248 #b, #B, #o, #x, and #X presentation types misformat negative numbers
Reviewed By: #libc, ldionne, vitaut
Differential Revision: https://reviews.llvm.org/D103433
Implements the formatter for all string types.
[format.formatter.spec]/2.2
For each charT, the string type specializations
```
template<> struct formatter<charT*, charT>;
template<> struct formatter<const charT*, charT>;
template<size_t N> struct formatter<const charT[N], charT>;
template<class traits, class Allocator>
struct formatter<basic_string<charT, traits, Allocator>, charT>;
template<class traits>
struct formatter<basic_string_view<charT, traits>, charT>;
```
This removes the stub implemented in D96664.
Implements parts of:
- P0645 Text Formatting
- P1868 width: clarifying units of width and precision in std::format
Reviewed By: #libc, ldionne, vitaut
Differential Revision: https://reviews.llvm.org/D103425
Priorities below 101 are reserved for the implementation, so that's what
we should be using here. That is unfortunately only supported on more
recent versions of Clang. See https://reviews.llvm.org/D31413 for details.
Differential Revision: https://reviews.llvm.org/D95972
Implement P1391 (https://wg21.link/p1391) which allows
`std::string_view` to be constructible from any contiguous range of
characters.
Note that a different paper (http://wg21.link/P1989) handles the generic
range constructor for `std::string_view`.
Reviewed By: ldionne, Quuxplusone, Mordante, #libc
Differential Revision: https://reviews.llvm.org/D110718
In basic_string and vector, we've been encapsulating all exception
throwing code paths in helper functions of a base class, which are defined
in the compiled library. For example, __vector_base_common defines two
methods, __throw_length_error() and __throw_out_of_range(), and the class
is externally instantiated in the library. This was done a long time ago,
but after investigating, I believe the goal of the current design was to:
1. Encapsulate the code to throw an exception (which is non-trivial) in
an externally-defined function so that the important code paths that
call it (e.g. vector::at) are free from that code. Basically, the
intent is for the "hot" code path to contain a single conditional jump
(based on checking the error condition) to an externally-defined function,
which handles all the exception-throwing business.
2. Avoid defining this exception-throwing function once per instantiation
of the class template. In other words, we want a single copy of
__throw_length_error even if we have vector<int>, vector<char>, etc.
3. Encapsulate the passing of the container-specific string (i.e. "vector"
and "basic_string") to the underlying exception-throwing function
so that object files don't contain those duplicated string literals.
For example, we'd like to have a single "vector" string literal for
passing to `std::__throw_length_error` in the library, instead of
having one per translation unit.
However, the way this is achieved right now has two problems:
- Using a base class and exporting it is really weird - I've been confused
about this ever since I first saw it. It's just a really unusual way of
achieving the above goals. Also, it's made even worse by the fact that
the definitions of __throw_length_error and __throw_out_of_range appear
in the headers despite always being intended to be defined in the compiled
library (via the extern template instantiation).
- We end up exporting those functions as weak symbols, which isn't great
for load times. Instead, it would be better to export those as strong
symbols from the library.
This patch fixes those issues while retaining ABI compatibility (e.g. we
still export the exact same symbols as before). Note that we need to
keep the base classes as-is to avoid breaking the ABI of someone who
might inherit from std::basic_string or std::vector.
Differential Revision: https://reviews.llvm.org/D111173
e9ee517930 added support for using
winpthreads on Windows, enabled if `__WINPTHREADS_VERSION` was
defined (i.e. if winpthreads headers have been included before
including libcxx `__config`). This was fragile (libcxx changed
behaviour depending on what headers had been included externally
before), and was changed in a1bc823a59
to use pthreads on Windows whenever the pthread.h header was
available.
This is also fragile; pthread.h might be unavailable while building
libcxx but installed later, and available when users include the
libcxx headers.
In practice, in every modern setup for building libcxx for Windows
I've seen, users end up manually configuring it with
`LIBCXX_HAS_WIN32_THREAD_API=ON`, as the users may have winpthreads
installed (for other libraries/projects to use) while wanting to
build libcxx with the default win32 threading.
Don't automatically pick up pthreads on Windows even if the header
is available. Instead require the user to configure the libcxx
build with `LIBCXX_HAS_PTHREAD_API=ON` if that's desired.
Differential Revision: https://reviews.llvm.org/D110975
The existing tests for transform_view::iterator weren't quite right,
and can be simplified now that we have more of C++20 available to us.
Having done that, let's use the same pattern for iota_view::iterator
as well.
Differential Revision: https://reviews.llvm.org/D110774
This adds the width estimation functions to the std-format-spec.
Implements parts of:
- P0645 Text Formatting
- P1868 width: clarifying units of width and precision in std::format
Reviewed By: #libc, ldionne, vitaut
Differential Revision: https://reviews.llvm.org/D103413
This reverts part of commit b82683b2eb.
I hadn't intended to remove the `// -*- C++ -*-` comment line
from `libcxx/include/version`, only from the generated tests.
Thanks to Raul Tambre for the catch.
Even if these comments have a benefit in .h files (for editors that
care about language but can't be configured to treat .h as C++ code),
they certainly have no benefit for files with the .cpp extension.
Discussed in D110794.
Some of these were previously half-implemented in "ordering.h";
now they're all implemented, and tested.
Note that `constexpr` functions are implicitly `inline`, so the
standard wording omits `inline` on these; but Louis and I agree
that that's surprising and it's better to be explicit about it.
Differential Revision: https://reviews.llvm.org/D110515
Instead of using a base class to store the members and the optional
size, use [[no_unique_address]] to achieve the same thing without
needing a base class.
Also, as a fly-by:
- Change subrange from struct to class (per the standard)
- Improve the diagnostic for when one doesn't provide a size to the ctor of a sized subrange
- Replace this->member by just member since it's not in a dependent base anymore
This change would be an ABI break due to [[no_unique_address]], but we
haven't shipped ranges anywhere yet, so this shouldn't affect anyone.
Differential Revision: https://reviews.llvm.org/D110370
There's really no reason to even have two different enums here,
but *definitely* we shouldn't have *three*, and they don't need
so many synonymous enumerator values.
Differential Revision: https://reviews.llvm.org/D110516
In reaction to the issues raised by Richard in https://llvm.org/D109066,
this commit does not apply P1951 as a DR in previous standard modes,
since it breaks valid code.
I do believe it should be applied as a DR, however ideally we'd get some
sort of statement from the Committee to this effect (and all implementations
would behave consistently). In the meantime, only implement P1951 starting
with C++23 -- we can always come back and apply it as a DR if that's what
the Committee says.
Differential Revision: https://reviews.llvm.org/D110347
That macro was being defined but not used anywhere in libc++, so it
must be safe to remove it.
As a fly-by fix, also remove mentions of this macro in other places
in LLVM, to make sure they were not depending on the value defined in
libc++.
Differential Revision: https://reviews.llvm.org/D110289
Implements parts of P1614, including synth-three-way and three way comparison for std::pair.
Reviewed By: #libc, Quuxplusone, Mordante
Differential Revision: https://reviews.llvm.org/D107721
Instead of overloading `__to_address`, let's specialize `pointer_traits`.
Function overloads need to be in scope at the point where they're called,
whereas template specializations do not. (User code can provide pointer_traits
specializations to be used by already-included library code, so obviously
`__wrap_iter` can do the same.)
`pointer_traits<__wrap_iter<It>>` cannot provide `pointer_to`, because
you generally cannot create a `__wrap_iter` without also knowing the
identity of the container into which you're trying to create an iterator.
I believe this is OK; contiguous iterators are required to provide
`to_address` but *not* necessarily `pointer_to`.
Differential Revision: https://reviews.llvm.org/D110198
All supported compilers provide support for inline variables in C++17 now.
Also, as a fly-by fix, replace some uses of _LIBCPP_CONSTEXPR by just
constexpr.
The only exception in this patch is `std::ignore`, which is provided
prior to C++17. Since it is defined in an anonymous namespace, it always
has internal linkage anyway, so using an inline variable there doesn't
provide any benefit. Instead, `inline` was removed entirely on `std::ignore`.
Differential Revision: https://reviews.llvm.org/D110243
LWG 2447 is marked as `Complete`, but there is no `static_assert` to
reject volatile types in `std::allocator`. See the discussion at
https://reviews.llvm.org/D108856.
Add `static_assert` in `std::allocator` to disallow volatile types. Since this
is an implementation choice, mark the binding test as `libc++` only.
Remove tests that use containers backed by `std::allocator` that test
the container when used with a volatile type.
Reviewed By: ldionne, #libc
Differential Revision: https://reviews.llvm.org/D109056
Also, as a fly-by fix, use `inline` directly to define inline variables
(all compilers support it).
Differential Revision: https://reviews.llvm.org/D110208
These routines were add years ago during initial porting attempts to AIX and are mostly build hacks for routines which we're missing at the time, but are available now on recent AIX OS levels.
Thus builds on modern AIX OS levels no longer need these and they cause problems if you try to build the library with a generic triple (i.e. powerpc-ibm-aix) as we'll pull them in and encounter duplicate definitions from the OS.
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D110183
Neither the current C++2b draft, nor any revision of [p1135],
nor libstdc++, claims that `counting_semaphore` should be
default-constructible. I think this was just a copy-paste issue
somehow.
Also, `explicit` was missing from the constructor.
Also, `constexpr` remains missing; but that's probably more of a
technical limitation, since apparently there are some platforms
where we don't (can't??) use the atomic implementation and
have to rely on pthreads, which obviously isn't constexpr.
Differential Revision: https://reviews.llvm.org/D110042
This implements the generic std.format.spec framework for all types.
The Unicode support will be added in a separate patch.
Implements parts of:
- P0645 Text Formatting
Completes:
- LWG-3242 std::format: missing rules for arg-id in width and precision
- P1892 Extended locale-specific presentation specifiers for std::format
Reviewed By: #libc, ldionne, vitaut
Differential Revision: https://reviews.llvm.org/D103368
- Simplify the structure of the new tests.
- Test const containers as well as non-const containers,
since it's easy to do so.
- Remove redundant enable-iffing of helper structs' member functions.
(They're not instantiated unless they're called, and who would call them?)
- Fix indentation and use more consistent SFINAE method in <unordered_map>.
- Add _LIBCPP_INLINE_VISIBILITY on some swap functions.
Differential Revision: https://reviews.llvm.org/D109011
Now that __builtin_is_constant_evaluated() is present on all supported
compilers, we can use it to skip the UB-inducing assert in cases where
the computation might be happening at constexpr time.
Differential Revision: https://reviews.llvm.org/D101674
All supported compilers have supported `=delete` as an extension
in C++03 mode for many years at this point.
Differential Revision: https://reviews.llvm.org/D109942
The aim is to add the missing z/OS specific implementations for mbsnrtowcs and wcsnrtombs, as part of libc++.
Differential Revision: https://reviews.llvm.org/D98207
Summary:
AIX have 2 byte wchar in 32 bit mode and 4 byte wchar in 64 bit mode.
This patch add more missing short wchar handling under the existing _LIBCPP_SHORT_WCHAR macro.
Marked test case ctor_move.pass.cpp as XFAIL for 32-bit mode on AIX because UTF-8 constants used cannot be converted to 2-byte wchar (by xingxue).
Authored by: jasonliu
Reviewed by: ldionne, zibi, SeanP, libc++
Differential Revision: https://reviews.llvm.org/D100777
In other places in the code, we use lowercase spelling for things that
are not available in prior standards.
Differential Revision: https://reviews.llvm.org/D109435
Detected by evil-izing the widely used `MoveOnly` testing type.
I had to patch some tests that were themselves using its comma operator,
but I think that's a worthwhile cost in order to catch more places
in our headers that needed comma-proofing.
The trick here is that even `++ptr, SomeClass()` can find a comma operator
by ADL, if `ptr` is of type `Evil*`. (A comma between two operands
of non-class-or-enum type is always treated as the built-in
comma, without ADL. But if either operand is class-or-enum, then
ADL happens for _both_ operands' types.)
Differential Revision: https://reviews.llvm.org/D109414
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
These are specced as `inline constexpr auto`; the extra `const`
isn't doing anything except being inconsistent with the other CPOs.
Now all the implemented CPOs can be detected by
git grep 'inline constexpr auto.*fn' ../libcxx/include/
and I think that's beautiful.
There were basically two bugs here:
When C++20 `to_address` is called on `int arr[10]`, then `const _Ptr&` becomes
a reference to a const array, and then we dispatch to `__to_address<const int(&)[10]>`,
which, oops, gives us a `const int*` result instead of an `int*` result.
Solution: We need to provide the two standard-specified overloads of
`std::to_address` in exactly the same way that we provide two overloads
of `__to_address`.
When `__to_address` is called on a pointer type, `__to_address(const _Ptr&)`
is disabled so we successfully avoid trying to instantiate pointer_traits of
that pointer type. But when it's called on an array type, it's not disabled
for array types, so we go ahead and instantiate pointer_traits<int[10]>,
which goes boom. Solution: We need to disable `__to_address(const _Ptr&)`
for both pointer and array types. Also disable it for function types,
so that they get the nice error message; and put a test on it.
Differential Revision: https://reviews.llvm.org/D109331
Implementation of `three_way_comparable` and `three_way_comparable_with` concepts from <compare> header.
Please note that I have temporarily removed `<compare>` header from `<utility>` due to cyclic dependency that prevents using `<concepts>` header in `<compare>` one.
I tried to quickly resolve those issues including applying suggestions from @cjdb and dive deeper by myself but the problem seems more complicated that we thought initially.
I am in progress to prepare the patch with resolving this cyclic dependency between headers but for now I decided to put all that I have to the review to unblock people that depend on that functionality. At first glance the patch with resolving cyclic dependency is not so small (unless I find the way to make it smaller and cleaner) so I don't want to mix everything to one review.
Reviewed By: ldionne, cjdb, #libc, Quuxplusone
Differential Revision: https://reviews.llvm.org/D103478
This implements the initial version of the `std::formatter` class and its specializations. It also implements the following formatting functions:
- `format`
- `vformat`
- `format_to`
- `vformat_to`
- `format_to_n`
- `formatted_size`
All functions have a `char` and `wchar_t` version. Parsing the format-spec and
using the parsed format-spec hasn't been implemented. The code isn't optimized,
neither for speed, nor for size.
The goal is to have the rudimentary basics working, which can be used as a
basis to improve upon. The formatters used in this commit are simple stubs that
will be replaced by real formatters in later commits.
The formatters that are slated to be replaced in this patch series don't have
an availability macro to avoid merge conflicts.
Note the formatter for `bool` uses `0` and `1` instead of "false" and
"true". This will be fixed when the stub is replaced with a real
formatter.
Implements parts of:
- P0645 Text Formatting
Completes:
- LWG3539 format_to must not copy models of output_iterator<const charT&>
Reviewed By: ldionne, #libc, vitaut
Differential Revision: https://reviews.llvm.org/D96664
Those constructors are very easy to misuse -- one could easily think that
the size passed to the constructor is the size of the range to exhibit
from the subrange. Instead, it's a size hint and it's UB to get it wrong.
Hence, when it's cheap to compute the real size of the range, it's cheap
to make sure that the user didn't get it wrong.
Differential Revision: https://reviews.llvm.org/D108827
_LIBCPP_HAS_NO_LONG_LONG was only defined on FreeBSD. Instead, use the
using_if_exists attribute to skip over declarations that are not available
on the base system. Note that there's an annoying limitation that we can't
conditionally define a function based on whether the base system provides
a function, so for example we still need preprocessor logic to define the
abs() and div() overloads.
Differential Revision: https://reviews.llvm.org/D108630
The `insert_iterator::iter` member is defined as `Container::iterator` but
the standard requires `iter` to be defined in terms of `ranges::iterator_t` as
of C++20. So, if in C++20 or later, define the `iter` member as
`ranges::iterator_t`.
Original patch by Joe Loser!
Differential Revision: https://reviews.llvm.org/D108575
D103357 added some new concepts. Since the header `<concepts>` has moved
all its concepts to a separate header these new concepts feel out of
place. Move them to the appropriate header.
Reviewed By: #libc, Quuxplusone, ldionne
Differential Revision: https://reviews.llvm.org/D109075
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
There is a lot more we can do, in particular in <type_traits>, but this
removes some workarounds that were gated on checking a specific compiler
version.
Differential Revision: https://reviews.llvm.org/D108923
Clang used to support [[nodebug]] everywhere except on typedefs. Since
we don't support such old Clangs anymore, we can get rid of _LIBCPP_NODEBUG_TYPE
in favour of always using _LIBCPP_NODEBUG.
Differential Revision: https://reviews.llvm.org/D108996
`contiguous_iterator` requires the iterator type passed is either a
pointer type or that the element type of the iterator is a complete
object type. These constraints are not part of the current wording in
defining the `contiguous_iterator` concept - adjust the concept to
reflect this.
Inspired from discussion at https://reviews.llvm.org/D108645.
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D108855
This must have been meant to be friend-declaring operator!=, but it
turns out that it's not even necessary to make it a friend since it
does not access any private state.
rdar://82568613
This move the helper types `chars_format`, `to_chars_result` and
`from_chars_result` to a separate header. The first two are needed for
D70631 the third for consistency.
The header `__charconv/ryu.h` uses these types and it can't depend on the
types in `<charconv>` in a modular build. Moving them to the ryu header
would be an odd place and doesn't work since the header is included in the
middle of `<charconv>`.
Reviewed By: #libc, ldionne, Quuxplusone
Differential Revision: https://reviews.llvm.org/D108927
We don't use double underscores for private header names when they are
in a subdirectory with double underscores already.
Differential Revision: https://reviews.llvm.org/D108820
This patch implements the underlying mechanism for range adaptors. It
does so based on http://wg21.link/p2387, even though that paper hasn't
been adopted yet. In the future, if p2387 is adopted, it would suffice
to rename `__bind_back` to `std::bind_back` and `__range_adaptor_closure`
to `std::range_adaptor_closure` to implement that paper by the spec.
Differential Revision: https://reviews.llvm.org/D107098
We don't support any compiler that doesn't support C++14 constexpr when
compiling in C++14 mode anymore, so we can just assume that we have C++14
extended constexpr when compiling in C++14 mode. This allows us to remove
some workarounds for older compilers.
Differential Revision: https://reviews.llvm.org/D108638
Based on https://github.com/NuxiNL/cloudlibc, it appears that the CloudABI
project has been abandoned. This patch removes a bunch of CloudABI specific
logic that had been added to support that platform.
Note that some knobs like LIBCXX_ENABLE_STDIN and LIBCXX_ENABLE_STDOUT
coud be useful in their own right, however those are currently broken.
If we want to re-add such knobs in the future, we can do it like we've
done it for localization & friends so that we can officially support
that configuration.
Differential Revision: https://reviews.llvm.org/D108637
When `_Compare` is a function parameter already (so it's not `void`
and it's not an abominable function type), `add_lvalue_reference_t<_Compare>`
is simply a synonym for `_Compare&`. We don't need to pull in `<type_traits>`
and instantiate a template trait to figure that out.
Differential Revision: https://reviews.llvm.org/D108400
A few headers in algorithm include `<iterator>` when
`<__iterator/distance.h>` would suffice. Change them
to just include `<__iterator.distance.h>`.
Differential Revision: https://reviews.llvm.org/D108393
basic_string and vector currently have a hard dependency on the compiled
library because they need to call __vector_base_common::__throw_xxx(),
which are externally instantiated in the compiled library. That makes
sense when exceptions are enabled (because we're trying to localize the
exception-throwing code to the compiled library), but it doesn't really
make sense when exceptions are disabled, and the __throw_xxx functions
are just calling abort() anyways.
This patch simply overrides the __throw_xxx() functions so that they
don't rely on the compiled library when exceptions are disabled.
Differential Revision: https://reviews.llvm.org/D108389
`<type_traits>` was included in the first iteration of `<compare>` when
it was created as a monolithic header, then never removed. Removing it
now is a beneficial no-op since it is not guaranteed by the standard
and is already included by all of its subheaders.
Reviewed By: cjdb, #libc, Quuxplusone
Differential Revision: https://reviews.llvm.org/D107801
__split_buffer_common was entirely unused, and __deque_base_common
was unused except for two calls to __throw_out_of_range(), which have
been inlined.
The usual intent of the __xxx_base_common base classes is to localize
where the exception-throwing code is instantiated, however that wasn't
the case here because we never explicitly instantiated those base classes
in the shared library, unlike what we do for basic_string and vector.
Differential Revision: https://reviews.llvm.org/D108384
In the future, we'll want to rely exclusively on using_if_exists for this
job, but for now, only rely on it when the compiler supports that attribute.
That removes the possibility for getting the logic wrong.
Differential Revision: https://reviews.llvm.org/D108297
The `get` half of this machinery was already implemented, but the `tuple_size`
and `tuple_element` parts were hiding in [ranges.syn] and therefore missed.
Differential Revision: https://reviews.llvm.org/D108054
All supported compilers have supported deduction guides in C++17 for a
while, so this isn't necessary anymore.
Differential Revision: https://reviews.llvm.org/D108213
As explained in http://eel.is/c++draft/range.nonprop.cache#note-1, we
should allow copy and move elision to happen when calling emplace_deref
in non-propagating-cache. Before this change, the only way to emplace
into the non-propagating-cache was to call `__set(*it)`, which materialized
`*it` when binding it to the reference argument of `__set` and disabled
move elision.
As a fly-by change, this also renames `__set` to `__emplace` for consistency
and adds tests for it.
Differential Revision: https://reviews.llvm.org/D107932
All supported compilers implement __builtin_addressof. Even MSVC implements
addressof as a simple call to __builtin_addressof, so it would work if we
were to port libc++ to that compiler.
Differential Revision: https://reviews.llvm.org/D107905
efriedma noted that D104682 broke this test case, reduced from SPEC2006.
#include <istream>
bool a(std::istream a) {
return a.getline(0,0) == 0;
}
We can unbreak it by restoring the conversion to something-convertible-to-bool.
We chose `void*` in order to match libstdc++.
For more ancient history, see PR19460: https://bugs.llvm.org/show_bug.cgi?id=19460
Differential Revision: https://reviews.llvm.org/D107663
All supported compilers have implemented __has_unique_object_representations
for a while, so it's reasonable to remove the workaround.
Differential Revision: https://reviews.llvm.org/D107834
All supported compilers have been supporting __is_aggregate for a long
time now, so it's reasonable to remove this workaround.
Differential Revision: https://reviews.llvm.org/D107833
All supported compilers should support
_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED so this can be removed.
Reviewed By: ldionne, #libc, Quuxplusone
Differential Revision: https://reviews.llvm.org/D107239
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
Switching `__builtin_clzll` to `__libcpp_clz` should work on all
platforms and no longer require MSVC specific code.
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D107709
@tcanens pointed out the current behavior of the macro breaks the usage
pattern described in http://wg21.link/SD6
```
# if __has_include(<optional>)
# include <optional>
# if __cpp_lib_optional >= 201606
# define have_optional 1
# endif
```
To support this usage pattern the hard errror is removed. Instead the
header includes nothing but the `<version>` header.
Reviewed By: ldionne, #libc
Differential Revision: https://reviews.llvm.org/D107134
Also, improve tests for std::destroy and std::destroy_n so that they
check for array support.
These changes are part of http://wg21.link/p0896 (the One Ranges proposal).
Differential Revision: https://reviews.llvm.org/D106916
Arthur O'Dwyer