Re: [gentoo-dev] [RFC] Forced/automatic USE flag constraints (codename: ENFORCED_USE)

[Ciaran McCreesh <ciaran.mccreesh@googlemail.com>]

On Thu, 15 Jun 2017 18:37:16 +0200
Alexis Ballier <aballier@gentoo.org> wrote:
> > So you're saying that at the end of this, there's an ENFORCED_USE
> > solver that spits out some answer that may or may not be in any way
> > a sane solution to the conflict.
> > 
> > I don't see how that's helpful to a user.
> 
> Define sane.
> The definition of the solver is made to change the least possible of
> the inputs and is completely and easily predictable by the person
> writing the constraint. That is something I would call sane.

The problem is not just writing a resolver that spits out a valid
output. The problem is writing a resolver which will never go and
uninstall bash as a result of unintended combinations of inputs (which
Portage used to do, but there's now a special exception for system
packages, so it will only occasionally unexpectedly uninstall critical
packages that aren't explicitly in system due to virtuals instead).
This is *hard*.

A bad suggestion to the user is worse than no suggestion at all. Unless
you can safely determine that there aren't any unintended consequences
of your rule, the focus needs to be on producing good error messages
so the user can figure the problem out, not on producing bad solutions
that will confuse things even more.

-- 
Ciaran McCreesh