external/boost: clang-cl cannot use MSVC's ATOMIC_FLAG_INIT

The C++ standard leaves it unspecified how ATOMIC_FLAG_INIT is defined, and at
least MS Visual Studio 2017 version 15.9 defines it as {0}, asking for list-
initialization, but std::atomic_flag is no aggregate (it has a default ctor) and
has no suitable ctor for that initializer list.  Other standard library
implementations solve that by e.g. adding a std::atomic_flag ctor taking a bool
parameter, and defining ATOMIC_FLAG_INIT as std::atomic_flag(false); but MSVC
apparently relies on some non-standard behavior here that allows to initialize
std::atomic_flag from {0}.  But that is apparently not supported by clang-cl,
causing failures like

> [build CXX] workdir/UnpackedTarball/boost/libs/locale/src/shared/date_time.cpp
> In file included from workdir/UnpackedTarball/boost/libs/locale/src/shared/date_time.cpp:11:
> In file included from workdir/UnpackedTarball/boost\boost/thread/locks.hpp:10:
> In file included from workdir/UnpackedTarball/boost\boost/thread/lock_algorithms.hpp:11:
> In file included from workdir/UnpackedTarball/boost\boost/thread/lock_types.hpp:18:
> In file included from workdir/UnpackedTarball/boost\boost/thread/thread_time.hpp:9:
> In file included from workdir/UnpackedTarball/boost\boost/date_time/time_clock.hpp:17:
> In file included from external/boost/include\boost/shared_ptr.hpp:27:
> In file included from workdir/UnpackedTarball/boost\boost/shared_ptr.hpp:17:
> In file included from workdir/UnpackedTarball/boost\boost/smart_ptr/shared_ptr.hpp:36:
> workdir/UnpackedTarball/boost\boost/smart_ptr/detail/spinlock_pool.hpp(77,5): error: no matching constructor for initialization of 'std::atomic_flag'
>     BOOST_DETAIL_SPINLOCK_INIT, BOOST_DETAIL_SPINLOCK_INIT, BOOST_DETAIL_SPINLOCK_INIT, BOOST_DETAIL_SPINLOCK_INIT, BOOST_DETAIL_SPINLOCK_INIT,
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~
> workdir/UnpackedTarball/boost\boost/smart_ptr/detail/spinlock_std_atomic.hpp(81,38): note: expanded from macro 'BOOST_DETAIL_SPINLOCK_INIT'
> #define BOOST_DETAIL_SPINLOCK_INIT { ATOMIC_FLAG_INIT }
>                                      ^~~~~~~~~~~~~~~~
> C:/PROGRA~2/MIB055~1/2017/COMMUN~1/VC/Tools/MSVC/1416~1.270/Include\atomic(158,26): note: expanded from macro 'ATOMIC_FLAG_INIT'
> #define ATOMIC_FLAG_INIT        {0}
>                                 ^~~
> C:/PROGRA~2/MIB055~1/2017/COMMUN~1/VC/Tools/MSVC/1416~1.270/Include\atomic(169,2): note: candidate constructor not viable: no known conversion from 'int' to 'const std::atomic_flag' for 1st argument
>         atomic_flag(const atomic_flag&) = delete;
>         ^
> C:/PROGRA~2/MIB055~1/2017/COMMUN~1/VC/Tools/MSVC/1416~1.270/Include\atomic(168,2): note: candidate constructor not viable: requires 0 arguments, but 1 was provided
>         atomic_flag() noexcept = default;
>         ^

The internals of external/boost appear to be the only place where we currently
use ATOMIC_FLAG_INIT, and we can work around that easily by picking a different
backend in boost/smart_ptr/detail/spinlock.hpp for the problematic combination
of Clang and _MSC_VER 1916 (which may need to be extended to further MSVC
versions).

Change-Id: Ie6aa62556efbedd3897ad7803b546cb8088ebe10
Reviewed-on: https://gerrit.libreoffice.org/79967
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

0 files changed, 0 insertions, 0 deletions