there are plenty of extension packages one can install for octave by

pkg install <archive.xyz.tar>

however this is not possible within the current version of Octave in Spack:

pkg install specfun-1.1.0.tar.gz
mkoctfile: stripping disabled on this platform
make: *** [ellipj.oct] Error 1
mkoctfile -s ellipj.cc
Spack compiler must be run from Spack! Input 'SPACK_PREFIX' is missing.

pkg: error running `make' for the specfun package.

I suppose octave keeps compilers used during its build for later usage and then fails because Spack's compiler wrappers can't be used outside of spack. Any ideas how to fix it?