[LLVMbugs] [Bug 17649] New: regression in r193073

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17649

            Bug ID: 17649
           Summary: regression in r193073
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: mrmocool at gmx.de
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

http://llvm-reviews.chandlerc.com/D1762

gcc (v4.8.1, Ubuntu 13.10) does indeed reject
for ( ; ({ if (first) { first = 0; continue; } 0; }); )

but it still accepts Qt 4.8.4's foreach (which seems to be the same in Qt 5.2).
Clang now rejects even the most basic use of that.
Please clarify if it needs to be changed in clang, g++ or Qt.
It seems like the semantics of this extension aren't all that clear:
http://gcc.gnu.org/ml/gcc-help/2013-07/msg00155.html

Here's the partially preprocessed code:

#include <vector>
#include <iostream>

template <typename T>
class QForeachContainer
{
public:
    inline QForeachContainer(const T& t)
    : c(t), brk(0), i(c.begin()), e(c.end())
    {
    }
    const T c;
    int brk;
    typename T::const_iterator i, e;
};

int main()
{
    std::vector<int> v(10);
    for (QForeachContainer<__typeof__(v)> _container_(v);
         !_container_.brk && _container_.i != _container_.e;
         __extension__({ ++_container_.brk; ++_container_.i; })
        )
        for (int val = *_container_.i;
             ;
             __extension__({--_container_.brk; break; })
            )
            std::cout << val << " ";
}

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