Add 'optional' or 'recommended' metadata tags to portfile spec.

[c.herbig@…]

There are certain programs that are not actually required for a program to run, but provide additional functionality. I don't think that simply adding them as 'depends_run' ports is a good solution, #39880. For example, Yelp provides a help browser for many Gnome apps, but has many dependencies that, if any are broken, will appear to be problems with the main port to the user. Instead of forcing the user to install yelp as a dependency, it might be better to inform them at install or upgrade time that yelp is a recommended secondary install.

Another example is gnome-themes-standard. Again, it is not at all necessary, but people will expect gnome apps to look a certain way, after seeing screenshots or working with linux systems. Even though this example is more trivial to simply append as a runtime dep, perhaps some people feel that it is not wanted, or are using a different theme.

As such, my proposal is to add one or other of the aforementioned metadata tags, so it would look like this:

recommended_ports: yelp \

gnome-themes-standard

and show up to the user after installation is complete as

Recommended supplementary ports:
    yelp  ${description of yelp}
    gnome-themes-standard  ${description of port}

and let the user decide for themselves.