Enhancement request: make pycore_cell.h compile cleanly under C++

This isn’t a “real issue” report, since pycore_cell.h (and the helpers it declares) are internal implementation details, so I understand they’re not part of the stable/public API, not guaranteed to be C++-compatible, and may change or disappear in future CPython versions. I’m still asking about this because the fix is very small.

While adapting CinderX to FT-Python, we include pycore_cell.h from a C++ (in the JIT/codegen path for LOAD_DEREF / STORE_DEREF). This currently fails to compile under C++ unless -fpermissive is used.

pycore_cell.h already has extern "C" guards, so it looks intended to be usable from C++ in at least some capacity. Would it be acceptable to add an explicit cast so it compiles cleanly under C++?``

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What is the error message? What is your compiler (name/version)?

I think most compilers error or warn for this pattern in C++: https://gcc.godbolt.org/z/dvsoqvPzd

Typically with something like:

GCC:

<source>:8:18: error: invalid conversion from 'void*' to 'Foo*' [-fpermissive]
    8 |     return malloc(sizeof(Foo));
      |            ~~~~~~^~~~~~~~~~~~~
      |                  |
      |                  void*
Compiler returned: 1

Clang:

<source>:8:12: error: cannot initialize return object of type 'Foo *' with an rvalue of type 'void *'
    8 |     return malloc(sizeof(Foo));
      |            ^~~~~~~~~~~~~~~~~~~

clang version 19.1.2, it should be similar for other compilers, C++ is stricter on implicit conversions.

internal/pycore_cell.h:56:13: error: assigning to 'PyObject *' (aka '_object *') from incompatible type 'void *'
   56 |     value = _Py_atomic_load_ptr(&cell->ob_ref);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

pythongh-144490: Fix test_cppext: test the internal C API

gh-144490: Fix test_cppext: test the internal C API (#144536)

pythongh-144490: Test the internal C API in test_cppext

gh-144490: Fix C++ compatibility in pycore_cell.h (GH-144482)

pythongh-144490: Fix C++ compatibility in pycore_cell.h (pythonGH-144482

[3.14] gh-144490: Fix C++ compatibility in pycore_cell.h (GH-144482) (G…

pythongh-144490: Fix mimalloc debug build

pythongh-144490: Fix test_cppext on Windows

pythongh-144490: Fix test_cppext on Windows (python#144628)

[3.14] gh-144490: Test the internal C API in test_cppext (#144547)

gh-144490: Fix mimalloc debug build for C++ (#144620)

pythongh-144490: Test the internal C API in test_cext

[3.14] gh-144490: Test the internal C API in test_cext (#144678)

I modified test_cext (C) and test_cppext (C++) to test the internal C API on 3.14 and main branches. test_cppext now includes the pycore_cell.h header file.

Currently, test_cppext skips pycore_backoff.h and pycore_cell.h since they include mimalloc which emits C++ compiler warnings.

pythongh-144490: Fix test_cppext: test the internal C API (python#144536

pythongh-144490: Fix C++ compatibility in pycore_cell.h (pythonGH-144482

pythongh-144490: Fix test_cppext on Windows (python#144628)

pythongh-144490: Fix mimalloc debug build for C++ (python#144620)

pythongh-144490: Fix test_cppext: test the internal C API (python#144536

pythongh-144490: Fix C++ compatibility in pycore_cell.h (pythonGH-144482

pythongh-144490: Fix test_cppext on Windows (python#144628)

pythongh-144490: Fix mimalloc debug build for C++ (python#144620)

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Enhancement request: make pycore_cell.h compile cleanly under C++ #144490

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Enhancement request: make pycore_cell.h compile cleanly under C++ #144490

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vstinner commented on Feb 5, 2026

colesbury commented on Feb 5, 2026

yoney commented on Feb 5, 2026

vstinner commented on Feb 10, 2026

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