[Bug c++/85251] New: Using declaration for base class constructor looses explicit.

[maxim.yegorushkin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85251

            Bug ID: 85251
           Summary: Using declaration for base class constructor looses
                    explicit.
           Product: gcc
           Version: 6.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: maxim.yegorushkin at gmail dot com
  Target Milestone: ---

Example:

    #include <cstdio>

    struct A {
        template<class... Args>
        A(Args&&... args) { std::printf("%s\n", __PRETTY_FUNCTION__); }

        explicit A(int) { std::printf("%s\n", __PRETTY_FUNCTION__); }
    };

    struct B : A { using A::A; };

    int main(int ac, char**) {
        A a = ac;
        B b = ac;
    }

Outputs:

    A::A(Args&& ...) [with Args = {int&}]
    A::A(int)

Expected output (clang++-3.9.0 output):

    A::A(Args&& ...) [with Args = {int&}]
    A::A(Args&& ...) [with Args = {int&}]