https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100863
--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-10 branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:5c86e63cb0383a38ec3dea24e9b3fe2f6e312057 commit r10-10305-g5c86e63cb0383a38ec3dea24e9b3fe2f6e312057 Author: Jonathan Wakely <jwak...@redhat.com> Date: Tue Jul 20 15:20:41 2021 +0100 libstdc++: fix is_default_constructible for hash containers [PR 100863] The recent change to _Hashtable_ebo_helper for this PR broke the is_default_constructible trait for a hash container with a non-default constructible allocator. That happens because the constructor needs to be user-provided in order to initialize the member, and so is not defined as deleted when the type is not default constructible. By making _Hashtable derive from _Enable_special_members we can ensure that the default constructor for the std::unordered_xxx containers is deleted when it would be ill-formed. This makes the trait give the correct answer. This backport to gcc-10 includes the fix for PR 101583. Signed-off-by: Jonathan Wakely <jwak...@redhat.com> libstdc++-v3/ChangeLog: PR libstdc++/100863 * include/bits/hashtable.h (_Hashtable): Conditionally delete default constructor by deriving from _Enable_default_constructor. Construct that base-class explicitly in all non-forwarding, non-defaulted constructors. * testsuite/23_containers/unordered_map/cons/default.cc: New test. * testsuite/23_containers/unordered_set/cons/default.cc: New test. (cherry picked from commit 89ec3b67dbe856a447d068b053bc19559f136f43)
