id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
11380	Container library std forward declarations incorrect in std_fwd.hpp on libc++ with gcc	tsniatowski@…	Ion Gaztañaga	"std_fwd.hpp contains code to detect libc++ and try to forward declare some types there appropriately. However, the ifdef logic assumes that libc++ is only ever used on Clang, which is incorrect. It is possible to use libc++ with GCC, for example on Android where you generally choose the compiler and C++ library separately.

Currently, ""#if defined(__clang__) && defined(_LIBCPP_VERSION)"" is used to trigger libc++-specific style of forward declarations. Only _LIBCPP_VERSION should be checked, with a secondary __clang__ check to disable a warning.

As a side note, shouldn't there be a build-time setting to disable this std:: forwarding altogether? It feels fragile, and borderline UB. It sacrifices portability for some potential build speed improvement, which might not be the best choice for everyone."	Bugs	closed	To Be Determined	container	Boost Development Trunk	Problem	fixed