[Bug c++/52915] New: [C++11] Deleted default-constructor of anonymous unions not honored

[daniel.kruegler at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52915

             Bug #: 52915
           Summary: [C++11] Deleted default-constructor of anonymous
                    unions not honored
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: daniel.kruegler@googlemail.com


gcc 4.8.0 20120318 (experimental) in C++11 mode accepts the following code:

//---
struct S {
  int val;
  S(int v) : val(v) {}
};

void f() {
  union { S a; };
}
//---

This seems to violate to what the standard says. According to 9.5 p5:

"A union of the form
  union { member-specification } ;
is called an anonymous union; it defines an unnamed object of unnamed type."

combined with 12.1 p5 b6:

"A defaulted default constructor for class X is defined as deleted if:
[..]
— any [..] non-static data member with no brace-or-equal-initializer, has class
type M [..] and [..] M has no default constructor [..]"

The last item has the effect that the anonymous union defined in f() is a
union-like class that has a deleted default constructor, but the definition in
f() also defines an unnamed object of that type which is default-initialized.
It seems that gcc does not respect the last part of the semantics of this
declaration.