[libc++] __bit reference: error: cannot add 'abi_tag' attribute in a redeclaration

[T-Maxxx]

• 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(

[philnik777]

Do you have a reproducer?

[T-Maxxx]

Closed sources unfortunately. I'll try to create example this weekend.
__
Possible solution: assign _LIBCPP_HIDE_FROM_ABI to friends declarations:

  template <class _Dp, bool _IC>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI friend __bit_iterator<_Dp, false> __copy_aligned(
      __bit_iterator<_Dp, _IC> __first, __bit_iterator<_Dp, _IC> __last, __bit_iterator<_Dp, false> __result);
  template <class _Dp, bool _IC>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI friend __bit_iterator<_Dp, false> __copy_unaligned(
      __bit_iterator<_Dp, _IC> __first, __bit_iterator<_Dp, _IC> __last, __bit_iterator<_Dp, false> __result);
  template <class _Dp, bool _IC>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI friend __bit_iterator<_Dp, false>
  copy(__bit_iterator<_Dp, _IC> __first, __bit_iterator<_Dp, _IC> __last, __bit_iterator<_Dp, false> __result);
  template <class _Dp, bool _IC>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI friend __bit_iterator<_Dp, false> __copy_backward_aligned(
      __bit_iterator<_Dp, _IC> __first, __bit_iterator<_Dp, _IC> __last, __bit_iterator<_Dp, false> __result);
  template <class _Dp, bool _IC>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI friend __bit_iterator<_Dp, false> __copy_backward_unaligned(
      __bit_iterator<_Dp, _IC> __first, __bit_iterator<_Dp, _IC> __last, __bit_iterator<_Dp, false> __result);
  template <class _Dp, bool _IC>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI friend __bit_iterator<_Dp, false>
  copy_backward(__bit_iterator<_Dp, _IC> __first, __bit_iterator<_Dp, _IC> __last, __bit_iterator<_Dp, false> __result);
  template <class _Cl, class _Cr>
  _LIBCPP_HIDE_FROM_ABI friend __bit_iterator<_Cr, false>
      __swap_ranges_aligned(__bit_iterator<_Cl, false>, __bit_iterator<_Cl, false>, __bit_iterator<_Cr, false>);
  template <class _Cl, class _Cr>
  _LIBCPP_HIDE_FROM_ABI friend __bit_iterator<_Cr, false>
      __swap_ranges_unaligned(__bit_iterator<_Cl, false>, __bit_iterator<_Cl, false>, __bit_iterator<_Cr, false>);
  template <class _Cl, class _Cr>
  _LIBCPP_HIDE_FROM_ABI friend __bit_iterator<_Cr, false>
      swap_ranges(__bit_iterator<_Cl, false>, __bit_iterator<_Cl, false>, __bit_iterator<_Cr, false>);
  template <class _Dp>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI friend __bit_iterator<_Dp, false>
      rotate(__bit_iterator<_Dp, false>, __bit_iterator<_Dp, false>, __bit_iterator<_Dp, false>);
  template <class _Dp, bool _IC1, bool _IC2>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI friend bool
      __equal_aligned(__bit_iterator<_Dp, _IC1>, __bit_iterator<_Dp, _IC1>, __bit_iterator<_Dp, _IC2>);
  template <class _Dp, bool _IC1, bool _IC2>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI friend bool
      __equal_unaligned(__bit_iterator<_Dp, _IC1>, __bit_iterator<_Dp, _IC1>, __bit_iterator<_Dp, _IC2>);
  template <class _Dp, bool _IC1, bool _IC2>
  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI friend bool
      equal(__bit_iterator<_Dp, _IC1>, __bit_iterator<_Dp, _IC1>, __bit_iterator<_Dp, _IC2>);

[T-Maxxx]

@philnik777

Here you go. "headers" version is like we're mixing sources, headers and modules in our codebase, just redacted names out due to NDA. For "flat" versions all headers' content are included directly, so there are weird constructions like "import XXX" in global module fragment. Also for "flat" version I've removed any include/import except error emitters.

llvm-136289.zip

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: Max (T-Maxxx)

- 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(