Re: [gentoo-dev] GLEP 29 (USE groups) and negatives

[Jerome Brown]

Ciaran McCreesh wrote:
> http://www.gentoo.org/proj/en/glep/glep-0029.html
>
> We need to decide upon a solution to the -flags problem. The proposed
> solutions are:
>
> 1) Disallow all negatives. Disadvantages: we don't tend to disallow
> things just because users could shoot themselves in the foot with them.
>
> 2) Allow negatives, and document how to use them correctly.
> Disadvantages: sooner or later, some developer isn't going to read the
> docs, and will really really screw things up with a misunderstanding.
>
> 3) Reorder USE flags. Disadvantages: can't disable flags set by a group.
> Breaks existing USE lines.
>
> 4) Have portage warn on dodgy USE flag lines. Disadvantages: tricky,
> hard for the end user to figure out.
>
> 5) Use some weird tristate notation. Disadvantages: not everyone has the
> slightest clue what set theory is.
>
> I'm in favour of 2) personally, but others disagree. I'd like a proper
> discussion on this before trying to get the GLEP through.
>
How about another option?

6) Disallow -USE within groups, but allow -@GROUP

Looking through the GLEP, I notice that the examples of where problems
of allowing -USE flags in a group could be resolved by not allowing the
-USE but allowing -@GROUP. For example, the usage of @KDE and @GNOME
groups in the glep looks like this:

<quote glep>
If, for example, the KDE group turned off GNOME things and the GNOME
group turned off KDE things:

KDE X kde qt -gtk -gnome
GNOME X gtk gtk2 gnome -kde -qt

And a user wished to use both KDE and GNOME on a system, and so had USE
flags as follows:

USE="@KDE @GNOME"

They would end up with:

USE="X kde qt -gtk -gnome X gtk gtk2 gnome -kde -qt"

Which simplifies:

USE="X gtk gtk2 gnome -kde -qt"

This is clearly not the desired effect.
</quote>

If, however we disallowed negatives in the group, you would define them as:

KDE X kde qt
GNOME X gtk gtk2 gnome

Therefore to get the desired effect of the originally suggested @KDE or
@GNOME the user would put:

USE="@KDE -@GNOME" or
USE="@GNOME -@KDE"

and to get both would have

USE="@KDE @GNOME"

which would resolve correctly.

The issue comes with resolving the individual (@KDE -@GNOME or vice
versa) as both define X, and a -X comes from the other. I guess that
this could be resolved by defining that if a USE flag is defined in a
group, and another group negates it, that portage ignores the negation,
however if the negation is specified by the user in their USE line then
the negation is allowed: Therefore

USE="@GNOME -@KDE"

would resolve to

USE="X gtk gtk2 gnome -kde -qt"

and

USE="@GNOME -X"

would resolve to

USE="gtk gtk2 gnome -X"

Just my 0.02 Universal Currency
-- 
Jerome Brown
Technology Architect
Hub.Net

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