PyImport_Import does not fall back to default builtins

Bug report

Bug description:

When importing a module with PyImport_Import() inside an already running python which does have limited globals, the import fails due to missing __builtins__: https://github.com/python/cpython/blob/01ba7df49966eaf14f44962a77898840c70dda96/Python/import.c#L3914-L3921

It feels similar to this issue: https://github.com/python/cpython/pull/24564 but with a slightly different setup.

Originally reported for pyo3 here: https://github.com/PyO3/pyo3/issues/4913

Minimal reproducer below, fuller reproducer can be found here: https://gitlab.com/nertpinx/cpython_repr

#include <Python.h>

PyObject *
func(PyObject *self __attribute__((unused)),
     PyObject *arg)
{
    return PyImport_Import(arg);
}

static PyMethodDef method_def = {
    .ml_name = "func",
    .ml_meth = func,
    .ml_flags = METH_NOARGS,
    .ml_doc = "Reproducer function",
};

int
main(int argc __attribute__((unused)),
     char **argv __attribute__((unused)))
{
    Py_InitializeEx(0);

    PyObject *program = NULL;
    PyObject *globals = NULL;
    PyObject *supermodule = NULL;
    PyObject *py_func = NULL;

    supermodule = PyUnicode_FromString("supermodule");
    py_func = PyCFunction_NewEx(&method_def, NULL, supermodule);
    globals = PyDict_New();
    PyDict_SetItemString(globals, "func", py_func);

    program = Py_CompileString("func()", "<string>", Py_file_input);
    PyEval_EvalCode(program, globals, NULL);

    if (PyErr_Occurred()) {
        PyErr_Print();
        return 1;
    }

    return 0;
}

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Commencez par les lignes référencées de import.c autour de 3914-3921 et construisez le reproducer C minimal avec CPython 3.13. Vérifiez comment PyImport_Import gère les globals sans builtins, puis ajoutez un test de régression couvrant la configuration avec des globals limités. C’est terminé lorsque l’import réussit en utilisant les builtins par défaut au lieu d’échouer à cause de l’absence de builtins.