[Bug c++/80804] New: Default constructor improperly invoked in C++1z mode

[barry.revzin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80804

            Bug ID: 80804
           Summary: Default constructor improperly invoked in C++1z mode
           Product: gcc
           Version: 7.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: barry.revzin at gmail dot com
  Target Milestone: ---

>From StackOverflow (http://stackoverflow.com/q/44015848/2069064), this code:

#include <cstdio>
#include <initializer_list>

struct S {
  S() { std::printf("DEF "); }      // (1)
  S(std::initializer_list<int> il)  // (2)
    { std::printf("L=%zu ", il.size()); }
};

int main() {
  S x({});
}

in gcc 7.1 with -std=c++1z invokes the default constructor. In C++14 mode, it
invokes the initializer_list constructor, as does clang in both modes. But the
default constructor shouldn't be invoked, since {} isn't an expression so the
"guaranteed elision" bullet in dcl.init shouldn't apply.