Use of std::is_constructible with non-constructible arguments fails with error rather than returning false

[llvmbot]

Bugzilla Link	40271
Version	trunk
OS	Linux
Attachments	The output of clang -save-temps of the reproducer program.
Reporter	LLVM Bugzilla Contributor
CC	@dwblaikie,@zygoloid

Extended Description

The following program:

#include <type_traits>

template<class T, class Allocator>
struct my_container
{
my_container(int n, Allocator alloc = Allocator()) {}
};

template
struct my_not_default_constructible_allocator
{
// no default ctor
my_not_default_constructible_allocator(int) {}
};

int main()
{
bool result = std::is_constructible<my_container<int, my_not_default_constructible_allocator>, int>::value;

return 0;
}

Yields a compile time error:

$ clang -std=c++14 repro.cpp
repro.cpp:6:41: error: no matching constructor for initialization of 'my_not_default_constructible_allocator'
my_container(int n, Allocator alloc = Allocator()) {}
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/type_traits:976:24: note: in instantiation of default function argument expression for
'my_container<int, my_not_default_constructible_allocator >' required here
= decltype(::new _Tp(declval<_Arg>()))>
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/type_traits:977:24: note: in instantiation of default argument for '__test<my_container<int,
my_not_default_constructible_allocator >, int>' required here
static true_type __test(int);
^~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/type_traits:987:24: note: while substituting deduced template arguments into function template '__test' [with _Tp =
my_container<int, my_not_default_constructible_allocator >, _Arg = int, $2 = (no value)]
typedef decltype(__test<_Tp, _Arg>(0)) type;
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/type_traits:144:14: note: in instantiation of template class 'std::__is_direct_constructible_impl<my_container<int,
my_not_default_constructible_allocator >, int>' requested here
: public conditional<_B1::value, _B2, _B1>::type
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/type_traits:992:14: note: in instantiation of template class 'std::_and<std::is_destructible<my_container<int,
my_not_default_constructible_allocator > >, std::__is_direct_constructible_impl<my_container<int, my_not_default_constructible_allocator >, int> >' requested here
: public _and<is_destructible<_Tp>,
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/type_traits:1074:14: note: in instantiation of template class 'std::__is_direct_constructible_new_safe<my_container<int,
my_not_default_constructible_allocator >, int>' requested here
: public conditional<is_reference<_Tp>::value,
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/type_traits:1082:14: note: in instantiation of template class 'std::__is_direct_constructible_new<my_container<int,
my_not_default_constructible_allocator >, int>' requested here
: public __is_direct_constructible_new<_Tp, _Arg>::type
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/type_traits:1122:14: note: in instantiation of template class 'std::__is_direct_constructible<my_container<int,
my_not_default_constructible_allocator >, int>' requested here
: public __is_direct_constructible<_Tp, _Arg>
^
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0/../../../../include/c++/7.2.0/type_traits:1133:14: note: in instantiation of template class 'std::__is_constructible_impl<my_container<int,
my_not_default_constructible_allocator >, int>' requested here
: public __is_constructible_impl<_Tp, _Args...>::type
^
repro.cpp:18:22: note: in instantiation of template class 'std::is_constructible<my_container<int, my_not_default_constructible_allocator >, int>' requested here
bool result = std::is_constructible<my_container<int, my_not_default_constructible_allocator>, int>::value;
^
repro.cpp:13:3: note: candidate constructor not viable: requires 1 argument, but 0 were provided
my_not_default_constructible_allocator(int) {}
^
repro.cpp:10:8: note: candidate constructor (the implicit copy constructor) not viable: requires 1 argument, but 0 were provided
struct my_not_default_constructible_allocator
^
repro.cpp:10:8: note: candidate constructor (the implicit move constructor) not viable: requires 1 argument, but 0 were provided
1 error generated.

Other compilers accept the input as expected:

$ g++ -std=c++14 repro.cpp
$

Compiler details:

$ clang --version ; echo ; g++ --version
clang version 4.0.1-6 (tags/RELEASE_401/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

g++ (Ubuntu 7.2.0-8ubuntu3.2) 7.2.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Stack Overflow discussion: https://stackoverflow.com/questions/54099360/why-doesnt-this-use-of-stdis-constructible-compile
Godbolt reproducer: https://godbolt.org/z/UI5Hy5

clang -save-temps attached.