[BUG]: detail\typeid.h(16,14): fatal error : 'cxxabi.h' file not found

[Boris-Rasin]

Required prerequisites

• Make sure you've read the documentation. Your issue may be addressed there.
• Search the issue tracker and Discussions to verify that this hasn't already been reported. +1 or comment there if it has.
• Consider asking first in the Gitter chat room or in a Discussion.

What version (or hash if on master) of pybind11 are you using?

3.1.0

Problem description

Compile error when using clang in Visual Studio (clang-cl):

pybind11\include\pybind11\detail\typeid.h(16,14): fatal error : 'cxxabi.h' file not found

clang-cl defines __GNUG__, but has no <cxxabi.h> header.

Possible fix:

#if __has_include(<cxxabi.h>)
#  include <cxxabi.h>
#endif

Reproducible example code

Is this a regression? Put the last known working version here if it is.

Not a regression

[henryiii]

Asked Claude to investigate, report below.

🤖 AI text below 🤖

Thanks for the report. Some notes:

The guard at detail/typeid.h:15 is unchanged since 2017, so this is not a regression, as you say. The other <cxxabi.h> include, in pybind11.h, is already guarded with && !defined(__clang__), so it is not affected.

We cannot reproduce the premise. With clang++ --target=x86_64-pc-windows-msvc -dM -E, clang defines _MSC_VER and __clang__, but not __GNUC__ or __GNUG__. Can you please give the exact compiler and command line (clang version, platform toolset, and any -f flags such as -fno-ms-compatibility)? The -dM -E output for the macros above is also helpful.

The suggested fix is correct, but it must also cover the use of abi::__cxa_demangle at typeid.h:36. If only the include is guarded, the call has no declaration. Also, pybind11 still supports C++11, where __has_include is not guaranteed, so it needs a fallback:

#if defined(__GNUG__)
#    if !defined(__has_include) || __has_include(<cxxabi.h>)
#        define PYBIND11_HAS_CXXABI_H
#    endif
#endif
#if defined(PYBIND11_HAS_CXXABI_H)
#    include <cxxabi.h>
#endif

Then both #if defined(__GNUG__) blocks in typeid.h use PYBIND11_HAS_CXXABI_H.