Re: [gentoo-dev] Gentoo Prefix: on EPREFIX, ED and EROOT inside ebuilds

[Fabian Groffen]

On 13-11-2009 12:43:25 +0100, Ulrich Mueller wrote:
> In its November meeting [1], the council has unanimously expressed
> support for this proposal [2].
>
> However, there is need for additional discussion. From the council
> meeting log I could extract the following open questions:
>
>   1. What are the implications for non-prefix devs and users?

for devs: take note of EPREFIX, ED and EROOT, be aware what they mean
and eventually, use them in the right way.  This is not hard, since a
simple script[3] based on some heuristics can do the work in 98% of the
cases right.
for users: not an single bit, unless they look inside ebuilds

>   2. Should the Prefix team be allowed to do the necessary changes to
>      ebuilds themselves, or should it be done by the respective
>      maintainers?

The Prefix team is the equivalent of an arch team, only handling a big
bunch of arches [4].  Hence, keywording should be out of the question,
and just allowed.  Adding simple patches (to normal non-critical
ebuilds) used to be allowed AFAIR, so I see that as ok too.  In other
words, like darkside mentioned, I see our activities like those of an
arch team.

>   3. Are there any backwards compatibility or upgrade path issues for
>      eclasses that must still accept EAPI 0 (where the new ED, EROOT,
>      and EPREFIX variables are not defined)?

The backward and forward compatability is handled with conditional
code like:
  use prefix || local ED=${D}
or
  [[ -z ${ED} ]] && local ED=${D}

Since Zac checked in yesterday blacklisting of EPREFIX, EROOT and ED in
the main Portage branch, these variables hopefully soon become protected
in the sense that an externally set ED does not result in weird
behaviour of a Prefix aware eclass or ebuild when using the latter
approach, which is true forward compatible.
For your information, this was exactly what I asked for from the council.

>   4. EAPI numbering: Would this simply be added as an additional
>      feature to EAPI 3? Or should we have an intermediate EAPI slot,
>      e.g. 2.1 or 3 (and current EAPI 3 renamed to 4 in the latter
>      case)?

I don't care about this, but a fast EAPI is necessary to 1) rely on ED not
coming from outside, and 2) since we're defining ED, EROOT and EPREFIX
anyway, initialise ED and EROOT such that we don't need any conditional
code in ebuilds at all (and can just use ED where necessary).

>   5. Who is going to write the exact specification (PMS patch) for
>      this EAPI feature?

We agreed that I/Prefix team will give this a shot.

>   6. (Any question that I've missed?)

I guess most additional questions go beyond, and actually address the
real Prefix work, and its implications to Gentoo and many ebuilds, since
we have to touch around 2300 ebuilds, most with trivial changes, some
with heavy changes (think of the 32 patches that one needs to compile
Python...)

> Let's start the discussion now, in order to work out these details
> before the next council meeting (December 7th).
>
> Ulrich
>
> [1] <http://www.gentoo.org/proj/en/council/meeting-logs/20091109.txt>
>     (topic was discussed from 21:32 to 22:11 in the log's timezone)
> [2] <http://archives.gentoo.org/gentoo-dev/msg_2a62689c71f95e4de5699a330b8b5524.xml>
>

[3] http://overlays.gentoo.org/proj/alt/browser/trunk/prefix-overlay/scripts/eapify
[4] http://stats.prefix.freens.org/keywords-packages.png

-- 
Fabian Groffen
Gentoo on a different level