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

[William Hubbs <williamh@gentoo.org>]

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On Fri, Jul 25, 2014 at 03:54:53PM -0400, Ian Stakenvicius wrote:
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> On 25/07/14 03:51 PM, Pacho Ramos wrote:
> > El vie, 25-07-2014 a las 20:46 +0100, Ciaran McCreesh escribió:
> >> On Fri, 25 Jul 2014 21:44:02 +0200 Luis Ressel <aranea@aixah.de>
> >> wrote:
> >>> Okay, I didn't think of that. I'm not sure if the blocker deps
> >>> or the REQUIRED_USE would be more helpful for Portage, but
> >>> generally I think that the REQUIRED_USE error message is quite
> >>> hard to understand for unexperienced users -- much more so than
> >>> the error generated by a blocker dep.
> >> 
> >> ...and the fix for that is to scrap REQUIRED_USE and use
> >> pkg_pretend instead.
> >> 
> > 
> > Could you give an example to let us see how pkg_pretend could be
> > used to achieve the same as REQUIRED_USE?
> > 
> > Thanks
> > 
> > 
> 
> pkg_pretend() {
> 	if use heimdal && use mit-krb5; then
> 		eerror "Please set only one of the use following flags:"
> 		eerror "heimdal, mit-krb5"
> 		die "conflicting use flags set"
> 	fi
> }

I think this could get complicated really quick though.
For example, if I have an ebuild with three use flags,
flag1/flag2/flag3 with the requirement that one and only one of them
must be set, unless bash has an xor operator I don't know about, that
is going to need a lot of nesting etc to get right.

William


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