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GLEP: 55
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Title: Use EAPI-suffixed ebuilds (.ebuild-EAPI)
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Version: $Revision: 1.3 $
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Last-Modified: $Date: 2009/05/17 15:50:27 $
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Author: Piotr Jaroszyński <peper@gentoo.org>
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Status: Draft
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Type: Standards Track
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Content-Type: text/x-rst
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Created: 17-Dec-2007
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Post-History: 17-Dec-2007, 22-Dec-2007, 17-May-2009
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"A little learning is a dangerous thing; drink deep, or taste not the Pierian
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spring: there shallow draughts intoxicate the brain, and drinking largely
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sobers us again."
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-- Alexander Pope, An Essay on Criticism
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Abstract
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========
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This GLEP proposes usage of EAPI-suffixed file extensions for ebuilds (for
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example, foo-1.2.3.ebuild-1).
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Problem
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=======
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The current way of specifying the EAPI in ebuilds is flawed. In order to get the
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EAPI the package manager needs to source the ebuild, which itself needs the EAPI
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in the first place. Otherwise it imposes a serious limitation, namely every ebuild,
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using any of the future EAPIs, will have to be source'able by old package
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managers and hence there is no way to do any of the following:
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* Change the behaviour of inherit in any way (for example, to extend or change
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eclass functionality).
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* Add new global scope functions in any sane way.
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* Extend versioning rules in an EAPI - for example, addition of the scm
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suffix - GLEP54 [#GLEP54]_ or allowing more sensible version formats like
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``1-rc1``, ``1-alpha`` etc. to match upstream more closely.
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* Use newer bash features.
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Current behaviour
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=================
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Following subsections show what happens if you introduce any of the mentioned
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changes in an ebuild and try to install it with portage 2.1.6.13.
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Incompatible change of inherit (e.g. make it look in the package dir too)
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-------------------------------------------------------------------------
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``sys-apps/foo-1.ebuild``::
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EAPI="5"
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inherit "foo"
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DESCRIPTION=""
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HOMEPAGE=""
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SRC_URI=""
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...
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Result::
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*
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* ERROR: sys-apps/foo-1 failed.
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* Call stack:
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* ebuild.sh, line 1879: Called _source_ebuild
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* ebuild.sh, line 1818: Called source '/var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild'
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* foo-1.ebuild, line 6: Called inherit 'foo'
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* ebuild.sh, line 1218: Called die
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* The specific snippet of code:
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* [ ! -e "$location" ] && die "${1}.eclass could not be found by inherit()"
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* The die message:
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* foo.eclass could not be found by inherit()
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*
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* If you need support, post the topmost build error, and the call stack if relevant.
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* This ebuild is from an overlay: '/var/lib/gentoo/repositories/peper/'
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*
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!!! All ebuilds that could satisfy "sys-apps/foo" have been masked.
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!!! One of the following masked packages is required to complete your request:
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- sys-apps/foo-1 (masked by: corruption)
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Current portage looks for eclasses only in the ``eclass`` directory of a
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repository. This results in a fatal error and ebuild being masked by corruption
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- might be pretty confusing to users.
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New global scope function
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-------------------------
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``sys-apps/foo-1.ebuild``::
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EAPI="5"
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new_global_scope_function "foo"
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DESCRIPTION=""
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HOMEPAGE=""
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SRC_URI=""
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...
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Result::
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/var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild: line 7: new_global_scope_function: command not found
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!!! All ebuilds that could satisfy "sys-apps/foo" have been masked.
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!!! One of the following masked packages is required to complete your request:
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- sys-apps/foo-1 (masked by: EAPI 5)
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The current version of portage supports EAPI '2'. You must upgrade to a
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newer version of portage before EAPI masked packages can be installed.
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Not that bad as user is advised to upgrade portage.
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New version format
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------------------
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``sys-apps/foo-2-rc1.ebuild``::
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Invalid ebuild name: /var/lib/gentoo/repositories/peper/sys-apps/foo/foo-2-rc1.ebuild
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emerge: there are no ebuilds to satisfy "sys-apps/foo"
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Not the best error message, especially if there are lots of them.
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Use newer bash features
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-----------------------
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``|&`` is a new type of redirection added in bash-4. It cannot be used even in
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local scope as bash still parses the whole ebuild.
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``sys-apps/foo-1.ebuild``::
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EAPI="5"
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foo() {
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echo "foo" |& cat
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}
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Result::
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/var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild: line 8: syntax error near unexpected token `&'
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/var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild: line 8: ` echo "foo" |& cat'
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*
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* ERROR: sys-apps/foo-1 failed.
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* Call stack:
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* ebuild.sh, line 1879: Called _source_ebuild
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* ebuild.sh, line 1818: Called die
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* The specific snippet of code:
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* source "${EBUILD}" || die "error sourcing ebuild"
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* The die message:
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* error sourcing ebuild
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*
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* If you need support, post the topmost build error, and the call stack if relevant.
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* This ebuild is from an overlay: '/var/lib/gentoo/repositories/peper/'
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* ... done!
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!!! All ebuilds that could satisfy "sys-apps/foo" have been masked.
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!!! One of the following masked packages is required to complete your request:
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- sys-apps/foo-1 (masked by: corruption)
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Again, not the best error.
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Abstract solution
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=================
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A solution to this problem has to lift those limitations and the only way to do
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it is to make the EAPI of an ebuild available to the package managers in a way
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that doesn't require them to source the ebuild. Another important requirement is
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for the solution to be backward compatible, which has the pleasant side-effect
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of making the solution applicable in the Gentoo tree right away. Opposed to
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waiting an arbitrary amount of time, which is never long enough anyway, as the
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issues listed on the common portage problems page - [#PortageProblems]_ - show.
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Proposed solution
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=================
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The proposed solution is to use EAPI-suffixed file extensions for ebuilds. This
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allows package managers to trivially read the EAPI from the ebuild filename. It
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is also backwards compatible, because currently ebuilds are recognised by the
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``.ebuild`` file extension and hence EAPI-suffixed ebuilds are simply ignored by
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the package managers.
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Specification
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=============
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Ebuild filename extension syntax: ``ebuild[-<EAPI>]``, where ``[]`` denotes an
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optional part, and ``<EAPI>`` is the EAPI of the ebuild.
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The EAPI used by the ebuild is the EAPI included in the filename if it is set.
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Otherwise the EAPI set inside the ebuild is used, which defaults to 0 (this is
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the current behaviour).
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Ebuilds with unsupported EAPIs are masked.
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It should be considered an error to set the EAPI both in the filename and in the
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ebuild.
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Examples:
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* ``pkg-1.ebuild``, no EAPI set inside the ebuild
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EAPI defaults to 0.
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* ``pkg-2.ebuild-1``, no EAPI set inside the ebuild
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EAPI 1 is used.
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* ``pkg-3.ebuild-1``, ``EAPI="1"``
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EAPI set in both places - error.
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Note that it is still not permitted to have more than one ebuild with equal
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category, package name, and version. Although it would have the advantage of
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allowing authors to provide backwards compatible ebuilds, it would introduce
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problems too. The first is the requirement to have strict EAPI ordering, the
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second is ensuring that all the ebuilds for a single category/package-version
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are equivalent, i.e. installing any of them has exactly the same effect on a
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given system.
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Summary of ideas
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================
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EAPI-suffixed ebuilds (proposed solution)
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-----------------------------------------
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Properties:
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* Can be used right away: yes
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* Hurts performance: no
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Some say it is clear and simple, others that it is ugly and unintuitive.
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EAPI in the filename with one-time extension change
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---------------------------------------------------
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One of the proposed filename formats:
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``<PKG>-<VER>.eapi-<EAPI>.eb``
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Properties:
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* Can be used right away: yes
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* Hurts performance: no
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This is equivalent to the proposed solution.
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Some say it is better because the extension is static.
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Easily fetchable EAPI inside the ebuild
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---------------------------------------
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Properties:
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* Can be used right away: no
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* Hurts performance: yes
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Cannot be used right away as it would trigger the errors shown in Current
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behaviour section for old package managers.
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Performance decrease comes from the fact that with version format changes in the
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picture package managers need EAPI to parse the ebuild's version. That means that merely
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picking the best version of a package requires loading EAPI (from cache or the
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ebuild) for each available ebuild.
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Easily fetchable EAPI inside the ebuild and one-time extension change
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---------------------------------------------------------------------
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Properties:
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* Can be used right away: yes
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* Hurts performance: yes
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Performance decrease as described in the previous section.
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Some say it is clear and simple, others that it is confusing and unintuitive,
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because of the arbitrary format restrictions in what is a bash script otherwise.
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Use different subdirectories for different EAPIs, i.e. cat/pkg/eapiX/
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---------------------------------------------------------------------
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Properties:
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* Can be used right away: yes
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* Hurts performance: yes
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Performance decrease comes from the fact that it adds several more directory
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reads.
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Some say that it makes it much harder for maintainers to see what they have.
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References
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==========
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.. [#GLEP54] GLEP 54, scm package version suffix
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(http://glep.gentoo.org/glep-0054.html)
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.. [#PortageProblems] Common portage problems
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(http://www.gentoo.org/proj/en/portage/doc/common-problems.xml)
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Copyright
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=========
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This document has been placed in the public domain.
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.. vim: set tw=80 fileencoding=utf-8 spell spelllang=en et :
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