invalid conversion from ‘void*’ to ‘_PyCodeArray*’ found in internal headers when compiling with Python 3.14t

[clin1234]

Bug report

Bug description:

Cross-reporting from scipy/scipy#21968 scipy/scipy#21970

Installing scipy from git with the free-threaded interpreter yielded the following errors:

[65/1464] Compiling C++ object scipy/special/_specfun.cpython-314t-x86_64-linux-gnu.so.p/meson-generated__specfun.cpp.o
      FAILED: scipy/special/_specfun.cpython-314t-x86_64-linux-gnu.so.p/meson-generated__specfun.cpp.o
      c++ -Iscipy/special/_specfun.cpython-314t-x86_64-linux-gnu.so.p -Iscipy/special -I../scipy/special -I../../../workspaces/venv/lib/python3.14t/site-packages/numpy/_core/include -I/usr/include/python3.14t -fvisibility=hidden -fvisibility-inlines-hidden -fdiagnostics-color=always -DNDEBUG -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -std=c++17 -O3 -fPIC -DNPY_NO_DEPRECATED_API=NPY_1_9_API_VERSION -MD -MQ scipy/special/_specfun.cpython-314t-x86_64-linux-gnu.so.p/meson-generated__specfun.cpp.o -MF scipy/special/_specfun.cpython-314t-x86_64-linux-gnu.so.p/meson-generated__specfun.cpp.o.d -o scipy/special/_specfun.cpython-314t-x86_64-linux-gnu.so.p/meson-generated__specfun.cpp.o -c scipy/special/_specfun.cpython-314t-x86_64-linux-gnu.so.p/_specfun.cpp
      In file included from /usr/include/python3.14t/internal/pycore_frame.h:13,
                       from scipy/special/_specfun.cpython-314t-x86_64-linux-gnu.so.p/_specfun.cpp:12385:
      /usr/include/python3.14t/internal/pycore_code.h: In function ‘_Py_CODEUNIT* _PyCode_GetTLBCFast(PyThreadState*, PyCodeObject*)’:
      /usr/include/python3.14t/internal/pycore_code.h:617:53: error: invalid conversion from ‘void*’ to ‘_PyCodeArray*’ [-fpermissive]
        617 |     _PyCodeArray *code = _Py_atomic_load_ptr_acquire(&co->co_tlbc);
            |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
            |                                                     |
            |                                                     void*
      In file included from scipy/special/_specfun.cpython-314t-x86_64-linux-gnu.so.p/_specfun.cpp:12385:
      /usr/include/python3.14t/internal/pycore_frame.h: In function ‘_Py_CODEUNIT* _PyFrame_GetBytecode(_PyInterpreterFrame*)’:
      /usr/include/python3.14t/internal/pycore_frame.h:96:53: error: invalid conversion from ‘void*’ to ‘_PyCodeArray*’ [-fpermissive]
         96 |     _PyCodeArray *tlbc = _Py_atomic_load_ptr_acquire(&co->co_tlbc);
            |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
            |                                                     |
            |                                                     void*
      [66/1464] Compiling C++ object scipy/special/_gufuncs.cpython-314t-x86_64-linux-gnu.so.p/_gufuncs.cpp.o
      [67/1464] Compiling C++ object scipy/special/_special_ufuncs.cpython-314t-x86_64-linux-gnu.so.p/_special_ufuncs.cpp.o
      ninja: build stopped: subcommand failed.
      [end of output]
  
  note: This error originates from a subprocess, and is likely not a problem with pip.
error: metadata-generation-failed

× Encountered error while generating package metadata.
╰─> See above for output.

note: This is an issue with the package mentioned above, not pip.
hint: See above for details.

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-127411: Fix invalid conversion of load of TLBC array when compiled in C++ #127466

[colesbury]

The header is C code, not C++, and it is internal only, not a public header.

Please see Ralf's comment on the SciPy issue for compiling SciPy with Cython 3.1.0a1.

[colesbury]

Oh - I think this should be referencing scipy/scipy#21970 instead.

Ralf wrote:

...it looks like it's Cython digging into CPython private internals, which have probably just changed. That tends to break regularly...

Yes, the Cython dependencies on CPython internals are a headache every release. I think some of them have been removed; it'd be great if we can remove the remaining deps.

In the meantime, we should just add a cast here so that it compiles in C++ as well.

cc @mpage.

[clin1234]

At a quick glance, a simple cast within the internal header should suffice, since the compilation error isn't pointing to a line within the generated C++ code

[ZeroIntensity]

Yeah, the bandaid is to just change it to _Py_CAST(_PyCodeArray*, _Py_atomic_load_ptr_acquire(&co->co_tlbc)).