<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 - conflicting types error when using '_com_ptr_t' on clang 9.0 RC"
   href="https://bugs.llvm.org/show_bug.cgi?id=42923">42923</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>conflicting types error when using '_com_ptr_t' on clang 9.0 RC
          </td>
        </tr>

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

        <tr>
          <th>Version</th>
          <td>9.0
          </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>release blocker
          </td>
        </tr>

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

        <tr>
          <th>Component</th>
          <td>-New Bugs
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>Zachary.Henkel@microsoft.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
          </td>
        </tr></table>
      <p>
        <div>
        <pre>clang 9.0 RC built with msvc version 19.22.27905 for x64.  The attached example
compiles fine on clang 8.0.1 and on msvc.  

An odd thing that I noticed is that -std=c++14 works fine, it's only -std=c++17
that causes these errors.

I've attached a fully preprocessed file in case an msvc installation & clang-cl
aren't handy.  Run clang -c -Wno-everything -std=c++17 min_repro.cpp

D:\>clang -c -Wno-everything -std=c++17  D:\temp\min_repro.cpp
D:\temp\min_repro.cpp:67792:16: error: conflicting types for '_com_ptr_t'
    template<> _com_ptr_t(Interface* pInterface) throw()
               ^
D:\temp\min_repro.cpp:68735:13: note: in instantiation of template class
'_com_ptr_t<_com_IIID<IUnknown,
      &__uuidof(IUnknown)> >' requested here
IUnknownPtr Foo() {
            ^
D:\temp\min_repro.cpp:67792:16: note: previous declaration is here
    template<> _com_ptr_t(Interface* pInterface) throw()
               ^
D:\temp\min_repro.cpp:67865:28: error: conflicting types for 'operator='
    template<> _com_ptr_t& operator=(Interface* pInterface) throw()
                           ^
D:\temp\min_repro.cpp:67865:28: note: previous declaration is here
D:\temp\min_repro.cpp:68011:21: error: conflicting types for 'operator=='
    template<> bool operator==(const _com_ptr_t& p) const throw()
                    ^
D:\temp\min_repro.cpp:68011:21: note: previous declaration is here
3 errors generated.

Optionally if an msvc command prompt is available:
D:\>type repro.cpp
#include <comdef.h>

IUnknownPtr Foo() {
    return nullptr;
}

D:\>clang-cl.exe -c -std:c++17 -TP -W0 repro.cpp
** Same Errors</pre>
        </div>
      </p>


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