Re: [gentoo-dev] Adding USE=udev to linux profiles

[Dennis Schridde]

On Friday, 20 July 2018 08:25:05 CEST Michael Orlitzky wrote:
> On 07/20/2018 02:12 AM, Mart Raudsepp wrote:
> > Ok, I can see that point of view for make.conf.
> > I can't agree with changes in other profiles though, as other profile
> > will fall under the same category in USE_ORDER (in fact, it's the same
> > thing, as the end USE from "defaults" comes from your selected profile
> > and it's "parent" cascade, not taken from linux profile). But maybe you
> > have it tested and know it's a problem. Have you?
>
> Yes, when you set USE=foo in profile A and USE="-foo" in profile A/B,
> the end result is USE="foo -foo" which is the same thing as USE="-foo".
> The default portage USE_ORDER makes the profile flags more important
> than IUSE defaults, so the USE="-foo" from the profile clobbers any
> IUSE="+foo" defaults.
>
> If no default was set in profile A, then no override would be necessary
> in profile A/B, and the resulting USE="" would not override the IUSE
> default.

It appears to me that the difficulty stems from use flags being tri-state 
(enabled, disabled, unset), but us having only operators to enable (+) and 
disable (-) them in make.conf and profiles.

What about adding a third operator, e.g. `^`, that resets a use flag to the 
unset state?