https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89510
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2020-04-30
Summary|new_allocator::construct |[9/10 Regression]
|needs to be constrained |new_allocator::construct
| |needs to be constrained
Known to work| |8.4.1
Keywords| |rejects-valid
Ever confirmed|0 |1
Assignee|unassigned at gcc dot gnu.org |redi at gcc dot gnu.org
Known to fail| |10.0, 9.3.1
Status|UNCONFIRMED |ASSIGNED
Target Milestone|--- |9.4
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This is actually a regression that breaks valid code:
#include <memory>
template<typename...> using void_t = void;
template<typename T, typename U, typename = void>
struct has_construct
: std::false_type
{ };
template<typename T, typename U>
struct has_construct<T, U,
void_t<decltype(std::declval<T&>().construct(std::declval<U*>()))>>
: std::true_type
{ };
struct X { X(int); };
constexpr bool b = has_construct<std::allocator<X>, X>::value;
In file included from
/home/jwakely/gcc/9/include/c++/9.2.1/x86_64-pc-linux-gnu/bits/c++allocator.h:33,
from
/home/jwakely/gcc/9/include/c++/9.2.1/bits/allocator.h:46,
from /home/jwakely/gcc/9/include/c++/9.2.1/memory:63,
from alloc.cc:1:
/home/jwakely/gcc/9/include/c++/9.2.1/ext/new_allocator.h: In instantiation of
'void __gnu_cxx::new_allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up =
X; _Args = {}; _Tp = X]':
alloc.cc:17:55: recursively required by substitution of 'template<class T,
class U> struct has_construct<T, U, void_t<decltype
(declval<T&>().construct(declval<U*>()))> > [with T = std::allocator<X>; U =
X]'
alloc.cc:17:55: required from here
/home/jwakely/gcc/9/include/c++/9.2.1/ext/new_allocator.h:145:20: error: no
matching function for call to 'X::X()'
145 | noexcept(noexcept(::new((void *)__p)
| ^~~~~~~~~~~~~~~~~~
146 | _Up(std::forward<_Args>(__args)...)))
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
alloc.cc:15:12: note: candidate: 'X::X(int)'
15 | struct X { X(int); };
| ^
alloc.cc:15:12: note: candidate expects 1 argument, 0 provided
alloc.cc:15:8: note: candidate: 'constexpr X::X(const X&)'
15 | struct X { X(int); };
| ^
alloc.cc:15:8: note: candidate expects 1 argument, 0 provided
alloc.cc:15:8: note: candidate: 'constexpr X::X(X&&)'
alloc.cc:15:8: note: candidate expects 1 argument, 0 provided
