[Bug c++/100065] New: Conditional explicit doesn't work for deduction guide

[andrey.davydov at jetbrains dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100065

            Bug ID: 100065
           Summary: Conditional explicit doesn't work for deduction guide
           Product: gcc
           Version: 10.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: andrey.davydov at jetbrains dot com
  Target Milestone: ---

#include <type_traits>

template<bool b>
struct X
{
    template<typename T>
    X(T);
};

template<bool b>
explicit(b) X(std::bool_constant<b>) -> X<b>;

X false_ = std::false_type{}; // #1 should be OK
X true_  = std::true_type{};  // #2 should fail, but GCC compiles it

Note that other compilers (Clang, MSVC) rejects case #2:
https://gcc.godbolt.org/z/fPEKn1no9