<html>
    <head>
      <base href="https://bugs.llvm.org/">
    </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 - decltype resolution doesn't terminate recursion"
   href="https://bugs.llvm.org/show_bug.cgi?id=40988">40988</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>decltype resolution doesn't terminate recursion
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>8.0
          </td>
        </tr>

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

        <tr>
          <th>OS</th>
          <td>Linux
          </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>C++11
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>Simon.Richter@hogyros.de
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
          </td>
        </tr></table>
      <p>
        <div>
        <pre>GCC exhibits the same bug, see
<a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89563">https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89563</a>

I'm trying to build a commutative operator+ for a class, as a freestanding
template operator+ that accepts my class on the right hand side and reverses
the argument order:

    struct one {};

    struct two
    {
        two() { }
        two(one const &) { }
        operator one() const { return one{}; }
        two operator+(one const &) const { return two{}; }
    };

    two operator+(two const &, two const &) { return two{}; }

    template<typename T>
    auto operator+(T const &lhs, two const &rhs) -> decltype(rhs + lhs)
    {
        return rhs + lhs;
    }

    void test()
    {
        one o;
        two t;
        auto a = o + t;
    }

This fails to compile, because the decltype for the return type is resolved
recursively through the template, even though a nontemplate function exists.
This remains the case even if I make a freestanding operator+(two const &, one
const &); 

icc and MSVC compile this code correctly.</pre>
        </div>
      </p>


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