Re: [gentoo-dev] On flags being in IUSE (and the prefix USE-flag in particular)

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

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On Mon, 10 Sep 2012 10:18:56 +0200
Fabian Groffen <grobian@gentoo.org> wrote:
> Normally, if you use a USE-flag, you add them to IUSE of the ebuild.
> However, some USE-flags have been considered too general to put them
> in there in the past.

That's not exactly why. Historically (as in, way before EAPI days) IUSE
was purely a visual thing: it was used for emerge -pv output, but not
anything affecting behaviour. Thus, people didn't list things that
weren't worth showing to the user.

That all went out of the window when we got package.use, new-use
support, etc. At that point, IUSE had to be fairly accurate. It became
even more important when we introduced use dependencies and use
dependency defaults. Not having an accurate IUSE means that
dependencies like cat/pkg[prefix(-)] can't work. This is why the
original EAPI 3 tidied all this up properly.

Unfortunately, due to EAPI 3 becoming EAPI 4 and having some features
removed, use dependency defaults ended up being "supported" without
having the necessary information to make them work correctly in all
cases, and prefix ended up being supported but without the "prefix" use
flag being special.

So really we should just not support prefix at all in any EAPI before
5, and not have the whole "but define those prefix variables anyway"
hack in eclasses. But apparently people are preferring to go to great
lengths not to have to use newer EAPIs...

-- 
Ciaran McCreesh

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