[Bug c++/77566] New: Warnings (-Wextra) disappear for a public reference to the this pointer

[michele.caini at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77566

            Bug ID: 77566
           Summary: Warnings (-Wextra) disappear for a public reference to
                    the this pointer
           Product: gcc
           Version: 6.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: michele.caini at gmail dot com
  Target Milestone: ---

I'm referring to this question on SO:
http://stackoverflow.com/questions/39449946/reference-to-the-this-pointer-gcc-vs-clang

The following code compiles with warnings with -Wextra:

    struct A {
    private:
        A* const& this_ref{this};
    };

    int main() {
        A a{};
        (void)a;
    }

Relevant warning:

/data/user/0/com.n0n3m4.droidc/files/temp.c: In constructor 'constexpr A::A()':
/data/user/0/com.n0n3m4.droidc/files/temp.c:1:8: warning: a temporary bound to
'A::this_ref' only persists until the constructor exits [-Wextra]
 struct A {
        ^

The following code (public data member) has no warning instead:

    struct A {
        A* const& this_ref{this};
    };

    int main() {
        A a{};
        (void)a;
    }

I guess the same diagnostic issue should be detected for the second snippet.