Requiring a specific variant in depends_lib

[Akim Demaille]

Hi!

I (try to) maintain the package for vcsn, and there are failures
on the build farm.  For instance on:

https://build.macports.org/builders/ports-10.7_x86_64_legacy-watcher/builds/3533

which leads to

https://build.macports.org/builders/ports-10.7_x86_64_legacy-builder/builds/18172/steps/install-port/logs/stdio

which fails with:

--->  Fetching archive for vcsn

DEBUG: Executing proc-pre-org.macports.archivefetch-archivefetch-0
DEBUG: Active variants check for archivefetch-type install considers depends_lib depends_run: boost ccache gmp python35 graphviz py35-ipython
DEBUG: boost is installed with the following variants: +no_single+no_static+python27
DEBUG:   required: python35, forbidden: 
DEBUG:   rejected, because required variant python35 is missing
Error: org.macports.archivefetch for port vcsn returned: boost must be installed with +python35.


So my question is: how can I specify that requirement in the Portfile?
Currently it reads:

depends_lib         port:boost \
                   path:bin/ccache:ccache \
                   port:gmp \
                   port:python${python_version}

and I’d like to have something like "port:boost + python${python_version}",
but it does not work.

Or if I can’t say that, what can I do so that vcsn is properly built
on your buildfarm?

Thanks in advance.