<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/126081>126081</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang-diagnostic-error for boost include
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          chrchr-github
      </td>
    </tr>
</table>

<pre>
    ~~~c++
#include <boost/date_time/posix_time/posix_time.hpp>
~~~

After upgrading from clang19 to clang20-rc1, the line above causes this error:
~~~
boost/boost_1_73_0\boost/mpl/aux_/integral_wrapper.hpp:73:31: error: non-type template argument is not a constant expression [clang-diagnostic-error]
   73 |     typedef AUX_WRAPPER_INST( BOOST_MPL_AUX_STATIC_CAST(AUX_WRAPPER_VALUE_TYPE, (value - 1)) ) prior;
 | ^
boost/boost_1_73_0\boost/mpl/aux_/static_cast.hpp:24:47: note: expanded from macro 'BOOST_MPL_AUX_STATIC_CAST'
   24 | #   define BOOST_MPL_AUX_STATIC_CAST(T, expr) static_cast<T>(expr)
      | ^
~~~
This happens on Windows, but I don't see it here for some reason: https://godbolt.org/z/ooEnPzWqW
</pre>
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