Describe the issue:

This simple example.i file:

%module example

%{
#include <numpy/arrayobject.h>
%}

%init
%{
    import_array();
%}

Compiles correctly when using SWIG 4.3:

$ swig -python example.i
$ gcc -c example_wrap.c $(pkgconf python3 --cflags) $(pkgconf numpy --cflags)

However, with SWIG 4.4, I get the following compilation error:

$ gcc -c example_wrap.c $(pkgconf python3 --cflags) $(pkgconf numpy --cflags)
example_wrap.c: In function ‘SWIG_mod_exec’:
example_wrap.c:4148:3: error: returning ‘void *’ from a function with return type ‘int’ makes integer from pointer without a cast [-Wint-conversion]
 4148 |   import_array();
      |   ^~~~~~~~~~~~

It seems that the problem stems from the change in how SWIG generates the wrap file. In version 4.4, the code generated by _core/code_generators/generate_numpy_api.py became incompatible. I traced the problem down and found that it can be resolved by amending the code starting at line 160:

#define import_array() { \
  if (_import_array() < 0) { \
    PyErr_Print(); \
    PyErr_SetString( \
        PyExc_ImportError, \
        "numpy._core.multiarray failed to import" \
    ); \
    return NULL; \
  } \
}

changing the NULL to 0:

#define import_array() { \
  if (_import_array() < 0) { \
    PyErr_Print(); \
    PyErr_SetString( \
        PyExc_ImportError, \
        "numpy._core.multiarray failed to import" \
    ); \
    return 0; \
  } \
}

With SWIG 4.3, the import_array macro was included into a function that returned void. With SWIG 4.4, that function returns int (hence the GCC error above).

Reproduce the code example:

# Not applicable

Error message:

Python and NumPy Versions:

2.3.4
3.13.9 (main, Oct 15 2025, 14:56:22) [GCC 15.2.0]

Runtime Environment:

[{'numpy_version': '2.3.4',
'python': '3.13.9 (main, Oct 15 2025, 14:56:22) [GCC 15.2.0]',
'uname': uname_result(system='Linux', node='dev', release='6.16.5+deb14-amd64', version='#1 SMP PREEMPT_DYNAMIC Debian 6.16.5-1 (2025-09-05)', machine='x86_64')},
{'simd_extensions': {'baseline': ['SSE', 'SSE2', 'SSE3'],
'found': ['SSSE3', 'SSE41', 'POPCNT', 'SSE42'],
'not_found': ['AVX',
'F16C',
'FMA3',
'AVX2',
'AVX512F',
'AVX512CD',
'AVX512_SKX',
'AVX512_CLX',
'AVX512_CNL',
'AVX512_ICL',
'AVX512_SPR']}},
{'architecture': 'Nehalem',
'filepath': '/usr/lib/x86_64-linux-gnu/openblas-pthread/libopenblasp-r0.3.30.so',
'internal_api': 'openblas',
'num_threads': 2,
'prefix': 'libopenblas',
'threading_layer': 'pthreads',
'user_api': 'blas',
'version': '0.3.30'}]

Context for the issue:

This bug is causing the plplot package in Debian FTBFS (fail to build from source). See Bug#1119760.