[LLVMbugs] [Bug 16529] New: Regression: comma separated expressions in decltype() returns incorrect type in clang++3.3

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16529

            Bug ID: 16529
           Summary: Regression: comma separated expressions in decltype()
                    returns incorrect type in clang++3.3
           Product: clang
           Version: 3.3
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++11
          Assignee: unassignedclangbugs at nondot.org
          Reporter: mlesoinne at cmsoftinc.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

In the following simple example, the return type of decltype() is incorrect
resulting in an incorrect output. 

=====================Beginning of code==============================
#include <iostream>
#include <vector>


struct Yes { char x[2]; };
struct No { char x; };

template <typename T>
constexpr auto f(const T& t) -> decltype(t.end()-t.begin(), Yes{});

constexpr No f(...);

std::vector<int> v;
bool vecHasIteratorDiff = sizeof(f(v)) == sizeof(Yes);
bool intHasIteratorDiff = sizeof(f(3)) == sizeof(Yes);
int main() {
    int x;
    std::cout << vecHasIteratorDiff << std::endl;
    std::cout << intHasIteratorDiff << std::endl;
    return 0;
}
=======================End of code=================================
Output with clang++ 3.3: 
0
0

Expected output (and obtained with clang++ 3.2:
1
0

It seems clang++3.3 believes the decltype() is long. Changing Yes to a basic
type gets around the problem.

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