<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/136289>136289</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [libc++] __bit reference: error: cannot add 'abi_tag' attribute in a redeclaration
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            libc++
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          T-Maxxx
      </td>
    </tr>
</table>

<pre>
    - Clang: 20.1.3 (built from sources on tag)
- Using libc++
- C++20
- Affected by Modules feature - got error by implementing one of base classes as module.

```
In file included from /home/tmax/programs/clang-20/bin/../include/c++/v1/chrono:1009:
In file included from /home/tmax/programs/clang-20/bin/../include/c++/v1/__chrono/formatter.h:29:
In file included from /home/tmax/programs/clang-20/bin/../include/c++/v1/__chrono/ostream.h:40:
In file included from /home/tmax/programs/clang-20/bin/../include/c++/v1/sstream:323:
In file included from /home/tmax/programs/clang-20/bin/../include/c++/v1/__ostream/basic_ostream.h:27:
In file included from /home/tmax/programs/clang-20/bin/../include/c++/v1/bitset:137:
/home/tmax/programs/clang-20/bin/../include/c++/v1/__bit_reference:189:31: error: cannot add 'abi_tag' attribute in a redeclaration
  189 | _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __bit_iterator<_Cp, false> __copy_aligned(
      | ^
/home/tmax/programs/clang-20/bin/../include/c++/v1/__config:536:22: note: expanded from macro '_LIBCPP_HIDE_FROM_ABI'
  536 | __attribute__((__abi_tag__(_LIBCPP_TOSTRING(_LIBCPP_ODR_SIGNATURE))))
 | ^
/home/tmax/programs/clang-20/bin/../include/c++/v1/__bit_reference:986:67: note: previous declaration is here
  986 |   _LIBCPP_CONSTEXPR_SINCE_CXX20 friend __bit_iterator<_Dp, false> __copy_aligned(
      | ^
```
Another one
```
In file included from /home/tmax/programs/clang-20/bin/../include/c++/v1/vector:315:
In file included from /home/tmax/programs/clang-20/bin/../include/c++/v1/__vector/vector_bool.h:17:
/home/tmax/programs/clang-20/bin/../include/c++/v1/__bit_reference:189:31: error: cannot add 'abi_tag' attribute in a redeclaration
  189 | _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __bit_iterator<_Cp, false> __copy_aligned(
      | ^
/home/tmax/programs/clang-20/bin/../include/c++/v1/__config:536:22: note: expanded from macro '_LIBCPP_HIDE_FROM_ABI'
  536 | __attribute__((__abi_tag__(_LIBCPP_TOSTRING(_LIBCPP_ODR_SIGNATURE))))
 | ^
/home/tmax/programs/clang-20/bin/../include/c++/v1/__bit_reference:986:67: note: previous declaration is here
  986 |   _LIBCPP_CONSTEXPR_SINCE_CXX20 friend __bit_iterator<_Dp, false> __copy_aligned(
```
</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJzsV1Fv6yYY_TXkBSXCH05iP_jBdeO7SLtt1fZKfUMYf06YsIkAV-2_n3B8u2i60rTtLntphBQbAuc7R4cDkd7rw4BYkPUNWd8u5BiO1hXPy6_y7e1t0dj2vVjSysjhQHhJga2SFacEsmbUJtDO2Z56OzqFntqBBnkgkBNWLuk3r4cDNbpRBG5ii53V-RnY9FZ2HaqALW3e6VfbjgY97VCG0SFd0oMNFJ2zLg7r_mSwxyHERe2A1Ha0kR6pMtJ79FR62k9LrAgrY9uwubFyP9BOG6R6UGZssT2XTaA-2h4J1KGXbwTqk7MHJ3tPoFaR8BIYgbrRA4F6tSJQz_Pj-MwJ6tckvh6dHSzhZcJYTnh5DUwhZlSoO-t6GQK61ZHwEv6HCqwPDmU_4afsSvj-DEp4yYFfjfNMNf5eeq3EJXXYXqmMRgePIRqOz5A_lWOjg3DYocNBYUTJoqd4EiNg2pLxQclhsIHKtqUEtrLRYtr9WypDcLoZQ-RPJXXYojLSyaDtQFhJaZLllGwrKn7d31QPD6K6v3t63r08PIqn_V21E9XLC7CP0V_2tztRP95_FeXNnp6L0wGdDLGOSlQnAhXtpPFI-I4KoezpXUgTc60lkE2Q8RMhyXr3s8VSduh0TMc130QPQBRnsAEntd5OcvhwQC-Vs1GtH3IjsJ1qXfPNWR7xoaQQkQhkQsw6Tx3fV3m-f3p-3N99uei6v41ifrkrn7897mIkfzRW_ldC_Nk1eRb12Gwv9Tg5fNV29PTCE1R7ekSHE_k8O5Onf-GOzmkc2h_Y4fYf2OHirCgHG47o4hlz7VPkFdXEoeTJ-mpxNoN-RxeNtWbKsuQzWD6D5TNY_lawfMTFoi14m_NcLrBItmmab5PtOl0ciyzPFUeG2zZVIEG1bJNJxTmg4l0KyUIXwGDN0iRLGADnqyzN0nWK6QawSzlsSMqwl9qsjHntV9YdFtr7EYuEbyDLF0Y2aPx0nQe4uH0DxOu9K-KsZTMePEmZ0T74P9YJOpjpj8DFtPXtWQl6qf-_3KqL0ZniGMLJx4SBmkB90OE4Nitl470qFjR_LU_O_oYqRH9EltE-M9HXAn4PAAD__7tR4PM">