<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/62903>62903</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            c++20 nullptr_t should be in global namespace if <stddef.h> is included
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          gnbond
      </td>
    </tr>
</table>

<pre>
    According to [CPPReference](https://en.cppreference.com/w/cpp/types/nullptr_t), for versions up to C++20 nullptr_t should be in the global namespace if <stddef.h> is included.  I.e. the following code should compile:
```c++
#include <stddef.h>
void foo(nullptr_t) {}
``` 
According to Godbolt, this does compile for g++ from 10.1 onwards, but does not compile with clang 13-16. 

For C++2x nullptr_t should be in global namespace.

 It looks like stddef.h tries to implement this for the C++2x case, but there is a FIXME that is suspicious: https://github.com/llvm/llvm-project/blob/597dd1f91d9f3823e4184f1fe73d8125fa16c026/clang/lib/Headers/stddef.h#LL103C8-L103C8

</pre>
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