[Bug c++/77386] New: Explicit constructor is allowed causing ambiguous initialization call when it shouldn't be allowed

[hpmv at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77386

            Bug ID: 77386
           Summary: Explicit constructor is allowed causing ambiguous
                    initialization call when it shouldn't be allowed
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hpmv at google dot com
  Target Milestone: ---

Using g++ 4.8.4, compiling the following code

struct X{
  X(int, int) {}
};

struct Y {
 explicit Y(X) {}
 explicit Y(int, int) {}
};

int main() {
  Y({1, 2});
}


with the command line

  g++ -Wall -Wextra --std=c++11 main.cpp

fails with the errors

main.cpp: In function ‘int main()’:
main.cpp:11:11: error: call of overloaded ‘Y(<brace-enclosed initializer
list>)’ is ambiguous
   Y({1, 2});
           ^
main.cpp:11:11: note: candidates are:
main.cpp:6:11: note: Y::Y(X)
  explicit Y(X) {}
           ^
main.cpp:5:8: note: constexpr Y::Y(const Y&)
 struct Y {
        ^
main.cpp:5:8: note: constexpr Y::Y(Y&&)



This doesn't make sense because the overload Y::Y(const Y&) and Y::Y(Y&&)
should not be considered since it's not possible to interpret {1, 2} as Y(1, 2)
due to that constructor being marked explicit.

The code compiles in clang 3.4.