astropy.wcs incompatible with wcslib 6.3

As mentioned by @privong in issue #9018, there is an error on import with astropy.wcs with wcslib version 6.3 and astropy 3.2.1. The backtrace is the following:

/usr/lib/python3.7/site-packages/astropy/wcs/__init__.py in <module>
     24 """
     25 
---> 26 from .wcs import *
     27 from . import utils
     28 

/usr/lib/python3.7/site-packages/astropy/wcs/wcs.py in <module>
     47 from astropy.io import fits
     48 from . import docstrings
---> 49 from . import _wcs
     50 
     51 from astropy.utils.compat import possible_filename

ImportError: /usr/lib/libwcs.so.6: undefined symbol: fits_read_wcstab

Thanks!

[privong]

@nden The Arch package manager indicates that wcslib depends on cfitsio, so that dependency should be satisfied.

$ pacman -Qi wcslib
Name            : wcslib
Version         : 6.3-1
Description     : A C library that implements the 'World Coordinate System' (WCS) standard in FITS
[...]
Depends On      : cfitsio
[...]

[jhunkeler]

Thanks! I was completely baffled… I’m not sure if the wcslib maintainer needs a ping.

• --use-system-cfitsio links the FITS module against libcfitsio
• --use-system-wcslib links the WCS module against libwcs, and not libcfitsio.

In this case it feels like astropy/wcs/setup_package.py needs to be updated to link to cfitsio.

# Might be nothing more than
cfg['libraries'] = ['cfitsio']