Re: [gentoo-dev] USE_EXPAND / USE 'configuration space' refactoring: bikeshedding the separator

[Brian Harring <ferringb@gmail.com>]

On Thu, Sep 13, 2012 at 04:24:27PM +0100, Ciaran McCreesh wrote:
> On Thu, 13 Sep 2012 03:39:19 -0700
> Brian Harring <ferringb@gmail.com> wrote:
> > 1) We disallow '@' in USE flags (yes, a use flag can actually have 
> > '@' in it's name according to PMS; someone was hitting the crack 
> > pipe pretty damn hard when they allowed that one).  This doesn't 
> > impact anything in gentoo-x86, nor any tree I've ever seen.
> 
> No crack pipe was involved in that decision! It's because of LINGUAS.
> 
> (Incidentally, we used : rather than @ for separation for exheres-0 for
> that reason.)

Who says Linguas definition didn't involve a bit 'o crack? ;)  On that 
subject, not entirely sure how the hell a grepp'ing of profiles on my 
part missed that file; worse, I distinctly recall this coming up in 
the past.  Suspect it's time we add a footnote to that section of 
names since it's non-obvious.  Sigh...

Two angles;

1) Mind you, the woken up/caffeine ratio currently blows so this 
could be quite off kilter- but at first glance the '@' linguas usage 
actually seems to map to sub use groups (both in intent and 
grouping), at least for the quick scan I did of what we use.  Might 
not actually be an issue, iow if we allow that, although that's 
assuming the '@' subgroup approach translates reasonably cleanly.

The potential failure I'd see with that approach is it's a bit reliant 
on the assumption that the rules:

`language[_territory[.codeset]][@modifier]`

have been abided by- that the modifier is just that, a modifier.  
Were we to do this, which, at least at first sight, seems like a nifty 
solution that addresses it, we'd *likely* want sub groups to have a 
rule such that if you try to expand the subgroup of a setting, and 
that setting isn't a subgroup, it is considered 'on'.  Basically, for 
the linguas case, it kind of sucks if we get into the situation where 
the consuming ebuilds/eclasses has to be sensitive to which modifiers 
were exposed.  Essentially:

linguas@de_DE@, if not a subgroup to expand to, is treated as scalar, 
rather than list.  Impliciations of that I've not yet fully thought 
out- note that tweak isn't necessary for the basic notion of #1 to be 
usable also.


2) bikeshedding potentials: just spitballing a couple of potentials 
if '@' subgroups there doesn't fly for folks reading (mean it nicely, 
we shouldn't diverge arbitarily, but in the same instant we shouldn't 
import syntax/notions from exherbo unless they explicitly make sense 
in the gentoo/PMS context; the formats diverge enough the "reuse for 
compatibility" argument doesn't hold much water):

ruby_targets@ruby_18
ruby_targets:ruby_18
ruby_targets|ruby_18
ruby_targets(ruby_18)

Potentially fun thought, although the syntax is kind of ugly; 
basically we treat 'ruby_target' as a matching target (restriction in 
pkgcore vernacular, something that matches something else); the nice 
thing about this is it naturally plugins into the notion of multiple 
settings:

ruby_targets[ruby18]
ruby_targets[ruby18,ruby19]

In the same angle, while it's partially valid bash (and not in the 
single setting case):
ruby_targets{ruby_18}
ruby_targets{ruby_18,ruby_19}

That said, I consider the [] and {} syntax absolutely freaking ugly to 
the eye.  I mention it should others think it's not butt-fugly.

If approach #1 doesn't fly, using ':' as the delimiter gets my vote.

~harring