<html>
    <head>
      <base href="http://llvm.org/bugs/" />
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW --- - std::is_function<void()const> faild"
   href="http://llvm.org/bugs/show_bug.cgi?id=20084">20084</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>std::is_function<void()const> faild
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>libc++
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>unspecified
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Windows NT
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>All Bugs
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>y121516@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvmbugs@cs.uiuc.edu, mclow.lists@gmail.com
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>On clang HEAD and libcxx trunk, complile failed.


source:

#include<type_traits>

static_assert(std::is_function<void()const>{}, "");

int main(){}


compiler messages:

In file included from prog.cc:1:
/usr/local/libcxx-head/include/c++/v1/type_traits:438:83: error: no matching
function for call to '__source'
    : public integral_constant<bool,
sizeof(__libcpp_is_function_imp::__test<_Tp>(__libcpp_is_function_imp::__source<_Tp>()))
== 1>
                                                                               
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/libcxx-head/include/c++/v1/type_traits:443:14: note: in
instantiation of template class 'std::__1::__libcpp_is_function<void () const,
false>' requested here
    : public __libcpp_is_function<_Tp> {};
             ^
prog.cc:3:15: note: in instantiation of template class
'std::__1::is_function<void () const>' requested here
static_assert(std::is_function<void()const>{}, "");
              ^
/usr/local/libcxx-head/include/c++/v1/type_traits:429:28: note: candidate
template ignored: substitution failure [with _Tp = void () const]: reference to
function type 'void () const' cannot have 'const' qualifier
template <class _Tp> _Tp&  __source();
                     ~~~   ^
1 error generated.



It seems problem point is __libcpp_is_function_imp::__source function template
and changing clang behavior 3.4 to HEAD. 
please see: <a href="http://melpon.org/wandbox/permlink/7goraqrqNXsdOdLK">http://melpon.org/wandbox/permlink/7goraqrqNXsdOdLK</a></pre>
        </div>
      </p>
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