en/glep/glep-0055.txt

GLEP: 55
Title: Use EAPI-suffixed ebuilds (.ebuild-EAPI)
Version: $Revision: 1.2 $
Last-Modified: $Date: 2008/01/06 02:39:42 $
Author: Piotr Jaroszyński <peper@gentoo.org>
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 17-Dec-2007
Post-History: 17-Dec-2007, 22-Dec-2007, 17-May-2009

  "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 do any of the following:

  *  Change the 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]_ or allowing more sensible version formats like
     ``1-rc1``, ``1-alpha`` etc. to match upstream more closely.


Current behaviour
=================

Following subsections show what happens if you introduce any of the mentioned
changes in an ebuild and try to install it with portage 2.1.6.13.

Incompatible change of inherit (e.g. make it look in the package dir too)
-------------------------------------------------------------------------

``sys-apps/foo-1.ebuild``::

 EAPI="5"
 inherit "foo"

 DESCRIPTION=""
 HOMEPAGE=""
 SRC_URI=""
 ...

Result::

 *
 * ERROR: sys-apps/foo-1 failed.
 * Call stack:
 *               ebuild.sh, line 1879:  Called _source_ebuild
 *               ebuild.sh, line 1818:  Called source '/var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild'
 *            foo-1.ebuild, line    6:  Called inherit 'foo'
 *               ebuild.sh, line 1218:  Called die
 * The specific snippet of code:
 *              [ ! -e "$location" ] && die "${1}.eclass could not be found by inherit()"
 *  The die message:
 *   foo.eclass could not be found by inherit()
 *
 * If you need support, post the topmost build error, and the call stack if relevant.
 * This ebuild is from an overlay: '/var/lib/gentoo/repositories/peper/'
 *

 !!! All ebuilds that could satisfy "sys-apps/foo" have been masked.
 !!! One of the following masked packages is required to complete your request:
 - sys-apps/foo-1 (masked by: corruption)

Current portage looks for eclasses only in the ``eclass`` directory of a
repository. This results in a fatal error and ebuild being masked by corruption
- might be pretty confusing to users.

New global scope function
-------------------------

``sys-apps/foo-1.ebuild``::

 EAPI="5"
 new_global_scope_function "foo"

 DESCRIPTION=""
 HOMEPAGE=""
 SRC_URI=""
 ...

Result::

 /var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild: line 7: new_global_scope_function: command not found

 !!! All ebuilds that could satisfy "sys-apps/foo" have been masked.
 !!! One of the following masked packages is required to complete your request:
 - sys-apps/foo-1 (masked by: EAPI 5)

 The current version of portage supports EAPI '2'. You must upgrade to a
 newer version of portage before EAPI masked packages can be installed.

Not that bad as user is advised to upgrade portage.

New version format
------------------

``sys-apps/foo-2-rc1.ebuild``::

 Invalid ebuild name: /var/lib/gentoo/repositories/peper/sys-apps/foo/foo-2-rc1.ebuild

 emerge: there are no ebuilds to satisfy "sys-apps/foo"

Not the best error message, especially if there are lots of them.

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 backwards 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.

The EAPI used by the ebuild is the EAPI included in the filename if it is set.
Otherwise the EAPI set inside the ebuild is used, which defaults to 0 (this is
the current behaviour).

Ebuilds with unsupported EAPIs are masked.

It should be considered an error to set the EAPI both in the filename and in the
ebuild.

Examples:

  *  ``pkg-1.ebuild``, no EAPI set inside the ebuild
       EAPI defaults to 0.

  *  ``pkg-2.ebuild-1``, no EAPI set inside the ebuild
       EAPI 1 is used.

  *  ``pkg-3.ebuild-1``, ``EAPI="1"``
       EAPI set in both places - error.

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 authors to provide backwards 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 on a
given system.

Summary of ideas
================

EAPI-suffixed ebuilds (proposed solution)
-----------------------------------------

Properties:
 * Can be used right away: yes
 * Hurts performance: no

Some say it is clear and simple, others that it is ugly and unintuitive.

EAPI in the filename with one-time extension change
---------------------------------------------------

One of the proposed filename formats:
``<PKG>-<VER>.eapi-<EAPI>.eb``

Properties:
 * Can be used right away: yes
 * Hurts performance: no

This is equivalent to the proposed solution.

Some say it is better because the extension is static.

Easily fetchable EAPI inside the ebuild
---------------------------------------

Properties:
 * Can be used right away: no
 * Hurts performance: yes

Cannot be used right away as it would trigger the errors shown in Current
behaviour section for old package managers.

Performance decrease comes from the fact that with version format changes in the
picture package managers need EAPI to parse the ebuild's version. That means that merely
picking the best version of a package requires loading EAPI (from cache or the
ebuild) for each available ebuild.


Easily fetchable EAPI inside the ebuild and one-time extension change
---------------------------------------------------------------------

Properties:
 * Can be used right away: yes
 * Hurts performance: yes

Performance decrease as described in the previous section.

Some say it is clear and simple, others that it is confusing and unintuitive,
because of the arbitrary format restrictions in what is a bash script otherwise.

Use different subdirectories for different EAPIs, i.e. cat/pkg/eapiX/
---------------------------------------------------------------------

Properties:
 * Can be used right away: yes
 * Hurts performance: yes

Performance decrease comes from the fact that it adds several more directory
reads.

Some say that it 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 :
1	GLEP: 55
2	Title: Use EAPI-suffixed ebuilds (.ebuild-EAPI)
3	Version: $Revision: 1.2 $
4	Last-Modified: $Date: 2008/01/06 02:39:42 $
5	Author: Piotr Jaroszyński <peper@gentoo.org>
6	Status: Draft
7	Type: Standards Track
8	Content-Type: text/x-rst
9	Created: 17-Dec-2007
10	Post-History: 17-Dec-2007, 22-Dec-2007, 17-May-2009
11
12	"A little learning is a dangerous thing; drink deep, or taste not the Pierian
13	spring: there shallow draughts intoxicate the brain, and drinking largely
14	sobers us again."
15
16	-- Alexander Pope, An Essay on Criticism
17
18	Abstract
19	========
20
21	This GLEP proposes usage of EAPI-suffixed file extensions for ebuilds (for
22	example, foo-1.2.3.ebuild-1).
23
24	Problem
25	=======
26
27	The current way of specifying the EAPI in ebuilds is flawed. In order to get the
28	EAPI the package manager needs to source the ebuild, which itself needs the EAPI
29	in the first place. Otherwise it imposes a serious limitation, namely every ebuild,
30	using any of the future EAPIs, will have to be source'able by old package
31	managers and hence there is no way to do any of the following:
32
33	* Change the behaviour of inherit in any way (for example, to extend or change
34	eclass functionality).
35
36	* Add new global scope functions in any sane way.
37
38	* Extend versioning rules in an EAPI - for example, addition of the scm
39	suffix - GLEP54 [#GLEP54]_ or allowing more sensible version formats like
40	``1-rc1``, ``1-alpha`` etc. to match upstream more closely.
41
42
43	Current behaviour
44	=================
45
46	Following subsections show what happens if you introduce any of the mentioned
47	changes in an ebuild and try to install it with portage 2.1.6.13.
48
49	Incompatible change of inherit (e.g. make it look in the package dir too)
50	-------------------------------------------------------------------------
51
52	``sys-apps/foo-1.ebuild``::
53
54	EAPI="5"
55	inherit "foo"
56
57	DESCRIPTION=""
58	HOMEPAGE=""
59	SRC_URI=""
60	...
61
62	Result::
63
64	*
65	* ERROR: sys-apps/foo-1 failed.
66	* Call stack:
67	* ebuild.sh, line 1879: Called _source_ebuild
68	* ebuild.sh, line 1818: Called source '/var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild'
69	* foo-1.ebuild, line 6: Called inherit 'foo'
70	* ebuild.sh, line 1218: Called die
71	* The specific snippet of code:
72	* [ ! -e "$location" ] && die "${1}.eclass could not be found by inherit()"
73	* The die message:
74	* foo.eclass could not be found by inherit()
75	*
76	* If you need support, post the topmost build error, and the call stack if relevant.
77	* This ebuild is from an overlay: '/var/lib/gentoo/repositories/peper/'
78	*
79
80	!!! All ebuilds that could satisfy "sys-apps/foo" have been masked.
81	!!! One of the following masked packages is required to complete your request:
82	- sys-apps/foo-1 (masked by: corruption)
83
84	Current portage looks for eclasses only in the ``eclass`` directory of a
85	repository. This results in a fatal error and ebuild being masked by corruption
86	- might be pretty confusing to users.
87
88	New global scope function
89	-------------------------
90
91	``sys-apps/foo-1.ebuild``::
92
93	EAPI="5"
94	new_global_scope_function "foo"
95
96	DESCRIPTION=""
97	HOMEPAGE=""
98	SRC_URI=""
99	...
100
101	Result::
102
103	/var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild: line 7: new_global_scope_function: command not found
104
105	!!! All ebuilds that could satisfy "sys-apps/foo" have been masked.
106	!!! One of the following masked packages is required to complete your request:
107	- sys-apps/foo-1 (masked by: EAPI 5)
108
109	The current version of portage supports EAPI '2'. You must upgrade to a
110	newer version of portage before EAPI masked packages can be installed.
111
112	Not that bad as user is advised to upgrade portage.
113
114	New version format
115	------------------
116
117	``sys-apps/foo-2-rc1.ebuild``::
118
119	Invalid ebuild name: /var/lib/gentoo/repositories/peper/sys-apps/foo/foo-2-rc1.ebuild
120
121	emerge: there are no ebuilds to satisfy "sys-apps/foo"
122
123	Not the best error message, especially if there are lots of them.
124
125	Abstract solution
126	=================
127
128	A solution to this problem has to lift those limitations and the only way to do
129	it is to make the EAPI of an ebuild available to the package managers in a way
130	that doesn't require them to source the ebuild. Another important requirement is
131	for the solution to be backward compatible, which has the pleasant side-effect
132	of making the solution applicable in the Gentoo tree right away. Opposed to
133	waiting an arbitrary amount of time, which is never long enough anyway, as the
134	issues listed on the common portage problems page - [#PortageProblems]_ - show.
135
136	Proposed solution
137	=================
138
139	The proposed solution is to use EAPI-suffixed file extensions for ebuilds. This
140	allows package managers to trivially read the EAPI from the ebuild filename. It
141	is also backwards compatible, because currently ebuilds are recognised by the
142	``.ebuild`` file extension and hence EAPI-suffixed ebuilds are simply ignored by
143	the package managers.
144
145
146	Specification
147	=============
148
149	Ebuild filename extension syntax: ``ebuild[-<EAPI>]``, where ``[]`` denotes an
150	optional part, and ``<EAPI>`` is the EAPI of the ebuild.
151
152	The EAPI used by the ebuild is the EAPI included in the filename if it is set.
153	Otherwise the EAPI set inside the ebuild is used, which defaults to 0 (this is
154	the current behaviour).
155
156	Ebuilds with unsupported EAPIs are masked.
157
158	It should be considered an error to set the EAPI both in the filename and in the
159	ebuild.
160
161	Examples:
162
163	* ``pkg-1.ebuild``, no EAPI set inside the ebuild
164	EAPI defaults to 0.
165
166	* ``pkg-2.ebuild-1``, no EAPI set inside the ebuild
167	EAPI 1 is used.
168
169	* ``pkg-3.ebuild-1``, ``EAPI="1"``
170	EAPI set in both places - error.
171
172	Note that it is still not permitted to have more than one ebuild with equal
173	category, package name, and version. Although it would have the advantage of
174	allowing authors to provide backwards compatible ebuilds, it would introduce
175	problems too. The first is the requirement to have strict EAPI ordering, the
176	second is ensuring that all the ebuilds for a single category/package-version
177	are equivalent, i.e. installing any of them has exactly the same effect on a
178	given system.
179
180	Summary of ideas
181	================
182
183	EAPI-suffixed ebuilds (proposed solution)
184	-----------------------------------------
185
186	Properties:
187	* Can be used right away: yes
188	* Hurts performance: no
189
190	Some say it is clear and simple, others that it is ugly and unintuitive.
191
192	EAPI in the filename with one-time extension change
193	---------------------------------------------------
194
195	One of the proposed filename formats:
196	``<PKG>-<VER>.eapi-<EAPI>.eb``
197
198	Properties:
199	* Can be used right away: yes
200	* Hurts performance: no
201
202	This is equivalent to the proposed solution.
203
204	Some say it is better because the extension is static.
205
206	Easily fetchable EAPI inside the ebuild
207	---------------------------------------
208
209	Properties:
210	* Can be used right away: no
211	* Hurts performance: yes
212
213	Cannot be used right away as it would trigger the errors shown in Current
214	behaviour section for old package managers.
215
216	Performance decrease comes from the fact that with version format changes in the
217	picture package managers need EAPI to parse the ebuild's version. That means that merely
218	picking the best version of a package requires loading EAPI (from cache or the
219	ebuild) for each available ebuild.
220
221
222	Easily fetchable EAPI inside the ebuild and one-time extension change
223	---------------------------------------------------------------------
224
225	Properties:
226	* Can be used right away: yes
227	* Hurts performance: yes
228
229	Performance decrease as described in the previous section.
230
231	Some say it is clear and simple, others that it is confusing and unintuitive,
232	because of the arbitrary format restrictions in what is a bash script otherwise.
233
234	Use different subdirectories for different EAPIs, i.e. cat/pkg/eapiX/
235	---------------------------------------------------------------------
236
237	Properties:
238	* Can be used right away: yes
239	* Hurts performance: yes
240
241	Performance decrease comes from the fact that it adds several more directory
242	reads.
243
244	Some say that it makes it much harder for maintainers to see what they have.
245
246	References
247	==========
248
249	.. [#GLEP54] GLEP 54, scm package version suffix
250	(http://glep.gentoo.org/glep-0054.html)
251
252	.. [#PortageProblems] Common portage problems
253	(http://www.gentoo.org/proj/en/portage/doc/common-problems.xml)
254
255	Copyright
256	=========
257
258	This document has been placed in the public domain.
259
260	.. vim: set tw=80 fileencoding=utf-8 spell spelllang=en et :