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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 - Compiler crashes due to incorrect template pack syntax"
   href="https://bugs.llvm.org/show_bug.cgi?id=48465">48465</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Compiler crashes due to incorrect template pack syntax
          </td>
        </tr>

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

        <tr>
          <th>Version</th>
          <td>10.0
          </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++2a
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>dbronick@go.olemiss.edu
          </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>Created <span class=""><a href="attachment.cgi?id=24257" name="attach_24257" title="Crash synopsis including tmp files (sh and cpp), original run script, and stack dump">attachment 24257</a> <a href="attachment.cgi?id=24257&action=edit" title="Crash synopsis including tmp files (sh and cpp), original run script, and stack dump">[details]</a></span>
Crash synopsis including tmp files (sh and cpp), original run script, and stack
dump

Overview: When an unexpected, unexpanded parameter pack is encountered in the
template arguments of a concept, the compiler crashes.

Steps to Reproduce: Attempt to compile the following with clang++-10
-std=c++20:

=======================Begin Sample============================

template<typename... Ts>
concept test = requires{sizeof...(Ts);};//trivially true

template<typename... Ts>
requires test<Ts>
struct Test{};

int main()
{
        Test<>;
        return 0;
}

=======================End Sample==============================

Actual Result: The compiler crashes with a seg fault

Expected Result: A syntax error message about an unexpected parameter pack

Build Data & Hardware: 2020 December 9th on Ubuntu 20.04.1 LTS with kernel
5.4.0-56-generic</pre>
        </div>
      </p>


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