https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87366
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2018-10-01
CC| |jason at gcc dot gnu.org
Known to work| |4.9.4
Summary|SFINAE trait as template |[6/7/8/9 Regression] SFINAE
|parameter causes incorrect |trait as template parameter
|application of trait to |causes incorrect
|other areas |application of trait to
| |other areas
Ever confirmed|0 |1
Known to fail| |5.5.0, 6.4.0, 7.3.0, 8.2.0,
| |9.0
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:
struct A {};
struct B {};
template <typename T> struct wrapper {};
template <typename> struct enable_if_A { };
template<> struct enable_if_A<A> { using type = void; };
template <typename T, typename = typename enable_if_A<T>::type> using ok_t = T;
template <typename T> void not_even_called(wrapper<const ok_t<T>&> a);
template <typename T> int called(wrapper<const T&> a);
void test(wrapper<const B&>& val)
{
called(val);
}
87366.cc: In function 'void test(wrapper<const B&>&)':
87366.cc:17:15: error: no matching function for call to 'called(wrapper<const
B&>&)'
17 | called(val);
| ^
87366.cc:13:27: note: candidate: 'template<class T> int
called(wrapper<ok_t<T>&>)'
13 | template <typename T> int called(wrapper<const T&> a);
| ^~~~~~
87366.cc:13:27: note: template argument deduction/substitution failed:
87366.cc: In substitution of 'template<class T> int called(wrapper<ok_t<T>&>)
[with T = B]':
87366.cc:17:15: required from here
87366.cc:13:27: error: no type named 'type' in 'struct enable_if_A<B>'
This was accepted prior to gcc-5, it started to be rejected with r217250:
DR 1558
* pt.c (dependent_alias_template_spec_p): New.
(dependent_type_p_r): Handle dependent alias template
specialization.
(template_args_equal): A dependent alias template specializations
is not equal to its underlying type as a template argument.
* tree.c (strip_typedefs): Don't strip a dependent alias
template-id.
