How to avoid the need for both +emacs and +emacs_app

[Sean Farley]

On Tue, Sep 18, 2012 at 5:05 AM, Mojca Miklavec
<mojca.miklavec.lists at gmail.com> wrote:
> Hello,
>
> I recently received a feature request to add "+emacs_app" option to
> gnuplot in addition to "+emacs":
>     http://trac.macports.org/ticket/36135

[snip]

> From that point of view it seems a bit of an overkill to me to provide
> two options (result doesn't depends on which one was selected), it is
> only important that at least one emacs binary is present on the system
> and its full path is exposed to gnuplot.

Agreed. I've run into this with other emacs-derived ports (e.g. auctex)

> Does this call for an Emacs PortGroup with ${emacs_binary} variable?
> Any other suggestion? (One solution would definitely be to fix gnuplot
> in such a way that it wouldn't even have to call emacs, it would just
> copy the files, but that's an even bigger overkill.)

It looks that way. Or we could overload the path dependence syntax:
`depends_lib-append
path:bin/emacs:${applications_dir}/Emacs.app/Contents/MacOS/Emacs:emacs`
... but this seems rather ugly.

At the very least, we would need to decide how to specify an optional
dependence (such as gnuplot) vs. a mandatory dependence (such as
auctex). Are there any examples of this already?