[gentoo-dev] Re: RFC: USE flags in virtuals, to allow a specific provider to be determined

[Duncan]

Ian Stakenvicius posted on Fri, 25 Jul 2014 14:49:44 -0400 as excerpted:

> Hey all..  So, putting aside for now how much of a mess this would be to
> implement in the virtuals' ebuilds themselves, what do people think of
> changing the virtuals so that they contain an entry in IUSE for each
> provider that can satisfy it?
>
> The idea here is that the package satisfying a virtual could be
> optionally explicitly-chosen through package.use (or USE= in make.conf,
> perhaps) instead of having an entry in @world, that way if nothing
> depends on the virtual then it and the provider can be - --depclean'ed
> from the system. The idea is specifically NOT to have rdeps depend on
> these flags, that would undermine the whole purpose of the virtual; it
> would just be for end-users to set if they so chose.
>
> This may also help with getting portage to peg a virtual's provider to a
> specific package instead of constantly trying to switch from one to
> another, ie, how systemd kept getting pulled in, in relation to the
> upower virtual.

What about handling each such virtual_USE as a USE_EXPAND?  VIRTUAL_* as 
reserved-namespace USE_EXPAND would give us full backward compatibility 
along with an immediately identifiable namespace and virtually (heh) no 
possibility of confusion with other configuration.

Continuing with the earlier virtual/krb5 example, we'd have VIRTUAL_KRB5, 
with possible settings in make.conf of:

VIRTUAL_KRB5=mit-krb5
VIRTUAL_KRB5=heimdal

Virtually no possibility of confusion with normal USE flags, and the 
matching virtual would be immediately identifiable, so no possibility of 
getting confused on what it applies to, either.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman