Cython + numpy broken in Sage >= 10.8

[Eric Gourgoulhon]

Hi, 

The demo notebook

https://github.com/sagemanifolds/SageManifolds/blob/master/Notebooks/SM_black_hole_rendering.ipynb

used to work well up to Sage 10.7 (included). 

In Sage 10.8 and 10.9.beta5, it fails in cell 65 with the error message:

RuntimeError: command '/usr/bin/gcc' failed with exit code 1 /tmp/sage_3h57taol/spyx_bq4f9ism/_tmp_sage_3h57taol_tmp_c0x04if5_pyx/_tmp_sage_3h57taol_tmp_c0x04if5_pyx_0.c:1158:10: fatal error: numpy/arrayobject.h: Aucun fichier ou dossier de ce nom 1158 | #include "numpy/arrayobject.h"

This cell combines cython and numpy. 

My system is Ubuntu 24.04 and numpy is from Sage spkg since there is no system numpy installed on that computer. 

Following this thread

https://stackoverflow.com/questions/14657375/cython-fatal-error-numpy-arrayobject-h-no-such-file-or-directory

a workaround was to run

sudo ln -s /home/eric/sage/10.9/local/var/lib/sage/venv-python3.12.5/lib/python3.12/site-packages/numpy/_core/include/numpy/ /usr/include/numpy

Then the notebook ran successfully. 

So it seems that in the cython cell 65, the header files for numpy were searched in /usr/include/numpy (which did not exist), instead of in local/var/lib/sage/venv-python3.12.5/lib/python3.12/site-packages/numpy/_core/include/numpy/ under the Sage root directory. 

I've just checked that on the same computer, there is no such an issue with Sage 10.7. 

Eric.