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    <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 - "friends can only be classes or functions" should also be diagnosed when trying to befriend a concept"
   href="https://bugs.llvm.org/show_bug.cgi?id=45837">45837</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>"friends can only be classes or functions" should also be diagnosed when trying to befriend a concept
          </td>
        </tr>

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

        <tr>
          <th>Version</th>
          <td>trunk
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>All
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>All
          </td>
        </tr>

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

        <tr>
          <th>Severity</th>
          <td>enhancement
          </td>
        </tr>

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

        <tr>
          <th>Component</th>
          <td>C++2a
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>arthur.j.odwyer@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
          </td>
        </tr></table>
      <p>
        <div>
        <pre><a href="https://godbolt.org/z/jntYnj">https://godbolt.org/z/jntYnj</a>

Given this code:

struct S {
    template<class>
    friend concept fooable;
};

Clang produces this harsh syntax error:

error: expected member name or ';' after declaration specifiers
    friend concept fooable;
           ^

If you try to befriend any other kind of entity -- for example, a variable or
variable template -- Clang gives a much friendlier error message, indicating
that it understands what you were *trying* to do:

error: friends can only be classes or functions
    friend bool fooable_v;
                ^

People are already trying to befriend concepts in the field, so it would be
nice if Clang gave that same friendly error message
(diag::err_unexpected_friend) for the `concept` case, as well.</pre>
        </div>
      </p>


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