bug#22437: Fixing package-with-python2

[Andreas Enge <andreas@enge.fr>]

Hello,

this looks really good, but I do not understand why we need the
additional private variable, for instance %python-cython:

On Wed, Feb 03, 2016 at 09:47:15AM +0100, Ludovic Courtès wrote:
> -(define-public python-cython
> +(define %python-cython
>    (package
>      (name "python-cython")
>      (version "0.23.4")
> @@ -2946,8 +2946,13 @@ programming language and the extended Cython programming language.  It makes
>  writing C extensions for Python as easy as Python itself.")
>      (license asl2.0)))
>  
> +(define-public python-cython
> +  (package
> +    (inherit %python-cython)
> +    (properties `((python2-variant . ,(delay python2-cython))))))
> +
>  (define-public python2-cython
> -  (package (inherit (package-with-python2 python-cython))
> +  (package (inherit (package-with-python2 %python-cython))
>      (name "python2-cython")
>      (inputs

If python2-cython inherits from (package-with-python2 python-cython),
is not the only difference that it keeps the properties field? And
would this not be harmless, as we are not going to call package-with-python2
again? Or would this create a circular dependency with (delay python2-cython)?
(In C or Pascal, this would not be a problem, one could simply declare
things before they are used, and that is it.)

It would be more elegant to drop the additional variable if possible.

Andreas