Re: [gentoo-dev] Re: useflag policies

[Alexis Ballier]

On Wed, 12 Aug 2015 17:08:59 +0200
Ulrich Mueller <ulm@g.o> wrote:

> >>>>> On Wed, 12 Aug 2015, Alexis Ballier wrote:
>
> > i.e. something that really tells the PM how to automate the choice:
> > - 'qt5 -> !qt4' is rather straightforward to solve and tells the PM
> > how (note that it is not equivalent to 'qt4 -> !qt5')
> > - '^^ ( qt5 qt4 )' requires the PM to make a choice in order to
> >   automate it
>
> I was thinking about some syntax like this:
>
>    REQUIRED_USE="|| ( +foo bar ) ^^ ( +qt5 -qt4 )"
>
> The package manager would first evaluate each group in REQUIRED_USE
> with the original set of USE flags. If that doesn't evaluate to true,
> retry with flags changed as indicated by the + and - signs.


it is more in the line of what we currently do, but that doesn't
resolve the 'sat' problem: it doesnt make clear we don't want to
satisfy it but rather walk through a list of causes and consequences

now that i'm thinking more about it, killing || and ^^ would probably
solve the automation problem:
qt? ( !qt4? ( qt5 ) qt4? ( !qt5 ) ) vs 'qt? ( ^^ ( qt4 qt5 ) )'

a bit longer but PM now knows what to do


both are equally expressive:

|| ( a b ) <-> !a? ( b )
(or !b? ( a ) depending on preference)
Here PM will enable b if a is disabled (a if b is disabled in the
latter form)

^^ ( a b ) <-> !a? ( b ) a? ( !b )
Here PM will enable b if a is disabled; disable b if a is enabled


No need for a new syntax :)

Alexis.