Re: How to build Python3 support into GNATCOLL with alire

[Simon Wright <simon@pushface.org>]

Fabien Chouteau <fabien.chouteau@gmail.com> writes:

> We are considering adding the feature to Alire directly. In particular
> an easy way to get relevant info from pkg-config.

In the case of gnatcoll_python3, which already has
GNATCOLL_PYTHON_CFLAGS and GNATCOLL_PYTHON_LIBS environment vars, what
we need *for Homebrew* is to set the first to
  pkg-config --cflags-only-I python3-embed
and the second to
  pkg-config --libs-only-L python3-embed

Note the python3-embed! python3 on its own gives you no libs on
macOS. As far as I can tell this has been in Python since 3.8.

I did an experiment adding Homebrew to a new
gnatcoll_python3-23.0.1.toml and revised libpython3dev-external.toml,
and it successfully build a simple demo with the above environment
variables set externally.