[BUG]: Failed to build with gcc-4.x

[hdu-sdlzx]

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

v3.0.1

Problem description

The doc says:

Supported compilers
2. GCC 4.8 or newer

But actually pybind11 failed to compile with gcc-4.8.5:

$ g++ test.cpp -std=gnu++11 -I../pybind11/include -lpython3.8
In file included from ../pybind11/include/pybind11/detail/internals.h:12:0,
from ../pybind11/include/pybind11/detail/native_enum_data.h:9,
from ../pybind11/include/pybind11/cast.h:15,
from ../pybind11/include/pybind11/attr.h:14,
from ../pybind11/include/pybind11/detail/class.h:12,
from ../pybind11/include/pybind11/pybind11.h:12,
from test.cpp:1:
../pybind11/include/pybind11/conduit/pybind11_platform_abi_id.h:75:10: error: #error "Unknown platform or compiler: PLEASE REVISE THIS CODE."

error "Unknown platform or compiler: PLEASE REVISE THIS CODE."

      ^

This error is generated because _GLIBCXX_USE_CXX11_ABI which is introduced in gcc-5.x is not defined.
https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html

Are we going to fix gcc-4.x or raise the platform requirements?

Reproducible example code

#include "pybind11/pybind11.h"

int main()
{
    return 0;
}

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

v2.13.6

[hdu-sdlzx]

Still failed to build when -D_GLIBCXX_USE_CXX11_ABI is added:

$ g++ test.cpp -std=gnu++11 -I../pybind11/include -D_GLIBCXX_USE_CXX11_ABI -lpython3.8
In file included from ../pybind11/include/pybind11/attr.h:13:0,
from ../pybind11/include/pybind11/detail/class.h:12,
from ../pybind11/include/pybind11/pybind11.h:12,
from test.cpp:1:
../pybind11/include/pybind11/detail/common.h:209:49: error: missing binary operator before token "("
&& ((defined(__has_include) && __has_include(<string_view>)) || defined(_MSC_VER))
^
If __has_include is not defined, the compiler should stop at "defined(__has_include)" but actually it does not.
This looks like a c preprocessor bug.

[hdu-sdlzx]

The following change worked.

diff --git a/include/pybind11/conduit/pybind11_platform_abi_id.h b/include/pybind11/conduit/pybind11_platform_abi_id.h
index d21fdc56..93d45c31 100644
--- a/include/pybind11/conduit/pybind11_platform_abi_id.h
+++ b/include/pybind11/conduit/pybind11_platform_abi_id.h
@@ -71,6 +71,8 @@

define PYBIND11_BUILD_ABI \

         "_libstdcpp_gxx_abi_1xxx_use_cxx11_abi_" PYBIND11_PLATFORM_ABI_ID_TOSTRING(           \
             _GLIBCXX_USE_CXX11_ABI)

+# elif defined(GNUC) && (GNUC < 5)
+# define PYBIND11_BUILD_ABI "_gcc_4.x"

else

error "Unknown platform or compiler: PLEASE REVISE THIS CODE."

endif

diff --git a/include/pybind11/detail/common.h b/include/pybind11/detail/common.h
index 314dba40..2b0d897e 100644
--- a/include/pybind11/detail/common.h
+++ b/include/pybind11/detail/common.h
@@ -205,9 +205,10 @@

define PYBIND11_HAS_VARIANT 1

#endif

-#if defined(PYBIND11_CPP17) \

• && ((defined(__has_include) && __has_include(<string_view>)) || defined(_MSC_VER))
  -# define PYBIND11_HAS_STRING_VIEW 1
  +#if defined(PYBIND11_CPP17)
  +# if (defined(__has_include) && __has_include(<string_view>)) || defined(_MSC_VER)
  +# define PYBIND11_HAS_STRING_VIEW 1
  +# endif
  #endif

#if (defined(PYPY_VERSION) || defined(GRAALVM_PYTHON)) && !defined(PYBIND11_SIMPLE_GIL_MANAGEMENT)

[rwgk]

The documentation isn't accurate anymore, this just escaped everyone's attention.

The way I usually think about it:

• We really only support what we test.

Currently that's:

     93 MSVC 19.44.35219.0
     42 GNU 15.2.0
      1 GNU 14.2.0
      7 GNU 13.4.0
     82 GNU 13.3.0
      7 GNU 11.5.0
      8 GNU 11.4.0
     14 GNU 10.5.0
      2 GNU 10.2.1
      7 GNU 9.5.0
      7 GNU 8.5.0
     37 AppleClang 17.0.0.17000013
     26 AppleClang 15.0.0.15000100
     14 Intel 2021.10.0.20230609
      7 NVHPC 23.5.0
      7 Clang 21.1.0 with GNU-like command-line
      7 Clang 18.1.8
      7 Clang 16.0.6
      7 Clang 14.0.6
      7 Clang 11.1.0
      7 Clang 5.0.2

This counts how often cmake's The CXX compiler identification is ... appears in the CI logs.

According to https://gcc.gnu.org/releases.html, even GCC 5 was released already more than 10 years ago.

It's a real burden to have to support such ancient compilers. I actually hope we'll drop C++ 11 and C++ 14 support sometime soon.

How much of a hardship is it for you to just keep using pybind11 2.13.6?

[rwgk]

From the issue description:

The doc says:
Supported compilers
2. GCC 4.8 or newer

This reflects reality more accurately:

• Point main README.rst to CI for supported platforms and compilers #5910

[hdu-sdlzx]

Thank you for your reply.

How much of a hardship is it for you to just keep using pybind11 2.13.6?

I have no problem keep using pybind 2.x with old compilers. An updated doc is enough for me, thank you!