<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/61643>61643</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [C++20] [Modules] Including <valarray> in GMF in front of other headers may violate ODR Checking
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            libc++,
            clang:modules
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          ChuanqiXu9
      </td>
    </tr>
</table>

<pre>
    We meet the problem twice now (https://github.com/llvm/llvm-project/issues/61642 and https://github.com/llvm/llvm-project/issues/61150) so it may make sense to create a summary issue for this to avoid wider confusion. 

Here is the reproducer:

```
// a.cppm
module;
#include <ranges>
export module a;

// b.cppm
module;
#include <valarray>
#include <ranges>
export module b;
import a;
```

Compile it with:

```
clang++ -std=c++2b $(STL_PATH) a.cppm --precompile -o a.pcm
clang++ -std=c++2b $(STL_PATH) b.cppm -fmodule-file=a=a.pcm --precompile -o b.pcm
```

((STL_PATH) refer to libcxx HEAD in my reproducer). And it gives error diagnostics:

```
In module 'a' imported from b.cppm:5:
/home/chuanqi.xcq/workspace.xuchuanqi/llvm-project-for-work/build/61642/../../build_libcxx/include/c++/v1/variant:1743:16: error: 'std::__throw_if_valueless' has different definitions in different modules; definition in module 'a.<global>' first difference is function body
constexpr void __throw_if_valueless(_Vs&&... __vs) {
~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../build_libcxx/include/c++/v1/variant:1743:16: note: but in '' found a different body
constexpr void __throw_if_valueless(_Vs&&... __vs) {
~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In module 'a' imported from b.cppm:5:
/home/chuanqi.xcq/workspace.xuchuanqi/llvm-project-for-work/build/61642/../../build_libcxx/include/c++/v1/tuple:1562:1: error: 'std::__tuple_compare_three_way' has different definitions in different modules; definition in module 'a.<global>' first difference is function body
__tuple_compare_three_way(const tuple<_Tp...>& __x, const tuple<_Up...>& __y, index_sequence<_Is...>) {
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../build_libcxx/include/c++/v1/tuple:1562:1: note: but in '' found a different body
__tuple_compare_three_way(const tuple<_Tp...>& __x, const tuple<_Up...>& __y, index_sequence<_Is...>) {
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In module 'a' imported from b.cppm:5:
/home/chuanqi.xcq/workspace.xuchuanqi/llvm-project-for-work/build/61642/../../build_libcxx/include/c++/v1/__ranges/zip_view.h:494:40: error: 'std::__1::ranges::views::__zip::__fn::operator()' from module 'a.<global>' is not present in definition of 'std::__1::ranges::views::__zip::__fn' provided earlier
 _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Ranges&&... __rs) const
 ^
../../build_libcxx/include/c++/v1/__ranges/zip_view.h:491:40: note: declaration of 'operator()' does not match
  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()() const noexcept { return empty_view<tuple<>>{}; }
 ^
../../build_libcxx/include/c++/v1/__ranges/zip_view.h:494:40: note: declaration of 'operator()' does not match
  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Ranges&&... __rs) const
``` 

According to my analysis, this is caused by the free standing operators in <valarray> affects the operator in the require clause. We can find the example in https://github.com/llvm/llvm-project/issues/61150. And the compilation completes after I remove the free standing operator in valarray. Here is the example:


Although I add the libcxx tag, I am not sure that this is libcxx bug. I just add it to CC the libcxx folks. Since I met this in libstdc++ too. Maybe this is a defect in the spec.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzkWFtv6zYS_jX0y8CCTVm-PPjBl3iPgR704PTsdt8EihpZbCRSISlf-tDfvhhdbCc9G6TJLrbFGolIm8PhzDffkBwJ59RBIy5ZtGbRdiBqnxu73OS10E_qn_VikJj0svwZoUT04HOEypqkwBL8SUkEbU7A-Dz3vnIsXDG-Y3x3UD6vk0CakvFdURz7ZlhZ8wtKz_hOOVejY3w3HU8nHIRO4SM6xtGI8QU4A8pDKS5QikcEh9oheAPSovAIAlxdlsJeoJkKmbHgc-VIRByNSuGkUrQgjc5qp4wOgI22bLRqn5_QIpB0jmCxsiatJVqy-E6ITUfdX_u1cQZEIKuqbH8qTVoXyMJ1LxEqLYs6RWDhxgp9QMfCh3YQz5WxHtopIG6T7pUnb1V-FIWwVlyu6v_A2slVpyqb3--MeeFy89yYslIFUjxOyuevoyQLoQ-Mrxlfw9D5lIVb2X7lCTA-YXz-07cf4i-rb58ozC2aMBxWFmW3ztCACCpZvkth0inMWmeHmSIMt4L-SenvlkpuS33Xe8bnL5awmKElohUqkeczfHpYbUFpKC_3XOKLAFY6JdQO6ogO0FpjIVXioI3zSrrXgdzrPl6MzwTjM2ijhSlk1pQ9VcJVdNPDd7kpkfGdbLM-OMsnxncnYx9dJSQG57obeZGCw8zYIYkxvktqVaR9OjO-C4L-0YzErdeUtC3faLk2IIzvjmN6CKuE9ixcjWeTkJopC1ctANRhfNYEcsXCVRz73JpTrLL4KIoaC3SOnM2Fg1RlGVrUHlLMlFZeGe0I6dtAC5Fj4fpOpgnGDbuAhZtDYRJRUELwGWTKOn9VIpudIKu1bObSLtkxz2jn8VxZaDaU71s6j__hGJ8yPg2CAOL46IgibNYl1G_PPyx6-O0Nn3bufwx4bTxSm9SeoGF81qBgap2CuAPzz-P6X5j8vq5ox1mNoymn5jXmk2hMe5GwSBAjxidx-ZPQ_xX75g0_oHN1E3-rgiBotE8hjs-Mb-CFxN-fSVxIQukUz7HDp5qMIKG964XuaPRG3nz8896k-17A_3jG_X-i_RfO8zjuLll896uq4qPCU0B3o8liQs_RK3k_bjv9JY36NN3147-qqu9muu2ZCq3wxja3kUVDJsLntTRXjmgIlUVHVKN947ZFmOxDNvEZFQ9HlWIKKGyh0LbRgfiH_Xrz5Uv8ab99iHdff_wcr9Z7uJ0novYGXnozj792WN5OE9ucJs3ETjWLHt6bo_8-WONrsPqcTVEWwoo7mH4PfmqwRbcUXuadfe_0_eomaINniZWndASLvrYasKz8pTGYhZs-wSnC4QMl7WxLez81_0WMJv9zjN7Cj-v9-Vmlt5LS2FTpA13YywsILYqLU472xKZgVA6kqB2mkFyaejCziOC80M2s3pTm4H1eeIHIMpS-rSJ7ORJrq8qnWlkEWZDyAH5GkEJDpnTajONZlBUVVfqj1XJbZpDOtqppo0L9Aj06EJlHC3uwWJojvuIi2dK7F8B9idwZ-7JgaQEufG7qQw57EGlrR1cXeXEglPcgyoYHrra0vPBX4DvBpD4EsIdfaucbHcpTsDabe2WZKR5dAD8purDsocReiyYJ59OOzeCNCeCzuCR4XUbQzofS97FxFcpgkC7DdBEuxACX4-lsEUWTaBQO8uVcZKGMZhiNccbHcppkPJqLaMynUTIej8VALfmIh6OQh6NpFI14IBcpZjycIOeZmM45m4ywFKoIKG6BsYdBE7ElHTbhoBAJFq55TcM5edenIWd8wzhvC95w1d_tOGfRdmCXDQmS-uDYZFQo591NvVe-aF78bLrKeMSiLbBo_bnTEW1h3-Q9xfsFi5WGv33eUZNZoz3ls_E5WshRpGhd8xLmqEwhPMKP26-wyVE-Kn0Y1LZYfux1UfivAAAA__9D8hAp">