Default choices for port select (was: Re: py-mercurial)

[Sean Farley]

>> Sure it is. You could just generate the files needed during the
>> post-destroot phase. Something like this:
>>
>> 1) loop through ${python.prefix}/{bin,etc,share,lib,libexec}
>> 2) output into 'select' files: base, none, etc.
>
> And which port is supposed to install these files?
>
> Multiple ports want to provide options, but only one can claim ownership
> of the base file. The base file need to be retained even when I
> uninstall any of the ports providing options such that the other options
> can still be chosen.

(Apologies for the late reply)

This could be done in a similar way that subports work. For the bulk
majority of ports that need a 'select', generating the
${portname}-select would be trivial. For the edge cases, we could just
allow the options to be overridden. I think this would take care of
what you point out.

>> Well, couldn't something be done in the post-activate stage? "if nothing
>> selected, then select this one"
>
> Yes, the select port group could supply such a default post-activate phase.
>
> In some cases we also have system-provided option for which we decided
> they should be kept as the default. For example, when python27 is
> installed as a dependency of something else, should this change the
> 'python' executed in the shell or would the user recognize this as
> unexpected behavior? At the moment, the default would still be
> /usr/bin/python as no symlink has been placed in /opt/local/bin at all.
> Same is true for gcc4*/clang where the system-provided compiler is
> usually the better choice as it has been tested and is considered stable.

That isn't the case for MacPorts. The instructions have always (or
least for a long time) been to prepend ${prefix}/bin to your $PATH.
Whenever python27 or git or whatever is installed, it becomes the
default one used:

https://trac.macports.org/wiki/InstallingMacPorts

> However, there are other ports installed as a dependency that change
> what is executed by default - for example when git or svn are required
> for fetching. Also, ports like perl5* install as 'perl', overriding
> /usr/bin/perl in PATH. These ports do not provide a select option
> anyway, so is this the expected behavior?
>
> I am undecided on what the default option should be here...

Tough call. Though, I'm just suggesting we generate the
${portname}-select using something similar to subports.