[gentoo-commits] gentoo commit in xml/htdocs/proj/en/glep: glep-0001.txt glep-0055.txt

[Piotr Jaroszynski (peper)]

peper       08/01/05 02:36:36

  Modified:             glep-0001.txt
  Added:                glep-0055.txt
  Log:
  Add GLEP 55 txt.

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Index: glep-0055.txt
===================================================================
GLEP: 55
Title: Use EAPI-suffixed ebuilds (.ebuild-EAPI)
Version: $Revision: 1.1 $
Last-Modified: $Date: 2008/01/05 02:36:35 $
Author: Piotr Jaroszyński <peper@g.o>
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 17-Dec-2007
Post-History: 17-Dec-2007, 22-Dec-2007

  "A little learning is a dangerous thing; drink deep, or taste not the Pierian
  spring: there shallow draughts intoxicate the brain, and drinking largely
  sobers us again."

  -- Alexander Pope, An Essay on Criticism

Abstract
========

This GLEP proposes usage of EAPI-suffixed file extensions for ebuilds (for
example, foo-1.2.3.ebuild-1).

Problem
=======

The current way of specifying the EAPI in ebuilds is flawed. In order to get the
EAPI the package manager needs to source the ebuild, which itself needs the EAPI
in the first place. Otherwise it imposes a serious limitation, namely every ebuild,
using any of the future EAPIs, will have to be source'able by old package
managers and hence there is no way to:

  *  Change behaviour of inherit in any way (for example, to extend or change
     eclass functionality).

  *  Add new global scope functions in any sane way.

  *  Extend versioning rules in an EAPI - for example, addition of the scm
     suffix - GLEP54 [#GLEP54]_.


Abstract solution
=================

A solution to this problem has to lift those limitations and the only way to do
it is to make the EAPI of an ebuild available to the package managers in a way
that doesn't require them to source the ebuild. Another important requirement is
for the solution to be backward compatible, which has the pleasant side-effect
of making the solution applicable in the Gentoo tree right away. Opposed to
waiting an arbitrary amount of time, which is never long enough anyway, as the
issues listed on the common portage problems page - [#PortageProblems]_ - show.

Proposed solution
=================

The proposed solution is to use EAPI-suffixed file extensions for ebuilds. This
allows package managers to trivially read the EAPI from the ebuild filename. It
is also backward compatible, because currently ebuilds are recognised by the
``.ebuild`` file extension and hence EAPI-suffixed ebuilds are simply ignored by
the package managers.


Specification
=============

Ebuild filename extension syntax: ``ebuild[-<EAPI>]``, where ``[]`` denotes an
optional part, and ``<EAPI>`` is the EAPI of the ebuild.

Let's call the EAPI included in the ebuild filename the pre-source EAPI, and the
EAPI set inside the ebuild the post-source EAPI. Given these two, the final EAPI
used by the ebuild can be established by following these steps:

  *  If the pre-source EAPI is not set it defaults to 0.
  *  If the pre-source EAPI is not recognised it is returned immediately.
  *  If the post-source EAPI is not set, it defaults to the pre-source EAPI.
  *  post-source EAPI is returned.

The above process should be only used to generate the metadata cache. Should the
pre-source EAPI be unsupported the cache entry cannot be generated.

Ebuilds with unsupported EAPIs are masked.

QA tools should consider it an error for both EAPIs to be set explicitly to
different values. Package managers may warn, but must use the post-source EAPI
in such cases.

Examples:

  *  ``pkg-1.ebuild``, no EAPI set inside the ebuild
       pre-source EAPI defaults 0, post-source EAPI defaults to pre-source EAPI.
       EAPI 0 is used.

  *  ``pkg-2.ebuild-1``, no EAPI set inside the ebuild
       pre-source EAPI is 1, post-source EAPI defaults to pre-source EAPI.
       EAPI 1 is used.

  *  ``pkg-3.ebuild``, ``EAPI="1"``
       pre-source EAPI defaults to 0, post-source EAPI is 1.
       EAPI 1 is used.

  *  ``pkg-4.ebuild-2``, ``EAPI="1"``
       pre-source EAPI is 2, post-source EAPI is 1.
       EAPI 1 is used, but note that one should **never** explicitly set both
       EAPIs to different values.

  *  ``pkg-5.ebuild-2``, no EAPI set inside the ebuild, package manager not supporting EAPI 2
       pre-source EAPI is 2, post-source EAPI is never checked.
       ebuild masked because of the unsupported pre-source EAPI.

  *  ``pkg-6.ebuild``, ``EAPI="2"``, package manager not supporting EAPI 2
       pre-source EAPI defaults to 0, post-source EAPI is 2 (assuming the
       package manager didn't die when sourcing the ebuild thinking that EAPI 0
       is used).
       ebuild masked because of the unsupported post-source EAPI.

Note that it is still not permitted to have more than one ebuild with equal
category, package name, and version. Although it would have the advantage of
allowing to provide backward compatible ebuilds, it would introduce problems
too. The first is the requirement to have strict EAPI ordering, the second is
ensuring that all the ebuilds for a single category/package-version are
equivalent, i.e. installing any of them has exactly the same effect to the
system.

Application
===========

Note that the developers should only set the pre-source EAPI. The process
described above is only necessary to avoid undefined behaviour in corner cases
and to retain backwards compatibility.

QA tools may warn if the post-source EAPI is set at all, thus helping with the
transition to the new format.

Other ideas
===========

There were some other solutions proposed on the mailing list:

  *  Set the EAPI inside the ebuild in a way that makes it easy to fetch it
       *  Doesn't meet the backward compatibility requirement.
       *  Isn't forward compatible either.
       *  Could be confusing as ebuilds, and not without a reason, are
          considered bash scripts and this would impose additional restrictions.

  *  Do the above and change the ebuild extension to ``.ebuild-ng``
       *  Meets the backward compatibility requirement.
       *  Still can be confusing.
       *  Isn't really forward compatible. What would be after ``.ebuild-ng``?
          ``.ebuild-ng-ng``?

  *  Use different subdirectories for different EAPIs, i.e. cat/pkg/eapiX/
       *  Meets both requirements.
       *  Introduces a noticeable performance hit (several more directory reads
          in an I/O bound operation).
       *  Makes it much harder for maintainers to see what they have.


References
==========

.. [#GLEP54] GLEP 54, scm package version suffix
    (http://glep.gentoo.org/glep-0054.html)

.. [#PortageProblems] Common portage problems
    (http://www.gentoo.org/proj/en/portage/doc/common-problems.xml)

Copyright
=========

This document has been placed in the public domain.

.. vim: set tw=80 fileencoding=utf-8 spell spelllang=en et :



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