/[gentoo]/xml/htdocs/proj/en/glep/glep-0055.txt
Gentoo

Contents of /xml/htdocs/proj/en/glep/glep-0055.txt

Parent Directory Parent Directory | Revision Log Revision Log


Revision 1.2 - (show annotations) (download)
Sun Jan 6 02:39:42 2008 UTC (6 years, 7 months ago) by antarus
Branch: MAIN
Changes since 1.1: +15 -15 lines
File MIME type: text/plain
Editorially Bless glep 55 per changes I sent to peper

1 GLEP: 55
2 Title: Use EAPI-suffixed ebuilds (.ebuild-EAPI)
3 Version: $Revision: 1.1 $
4 Last-Modified: $Date: 2008/01/05 02:36:35 $
5 Author: Piotr JaroszyƄski <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
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]_.
40
41
42 Abstract solution
43 =================
44
45 A solution to this problem has to lift those limitations and the only way to do
46 it is to make the EAPI of an ebuild available to the package managers in a way
47 that doesn't require them to source the ebuild. Another important requirement is
48 for the solution to be backward compatible, which has the pleasant side-effect
49 of making the solution applicable in the Gentoo tree right away. Opposed to
50 waiting an arbitrary amount of time, which is never long enough anyway, as the
51 issues listed on the common portage problems page - [#PortageProblems]_ - show.
52
53 Proposed solution
54 =================
55
56 The proposed solution is to use EAPI-suffixed file extensions for ebuilds. This
57 allows package managers to trivially read the EAPI from the ebuild filename. It
58 is also backwards compatible, because currently ebuilds are recognised by the
59 ``.ebuild`` file extension and hence EAPI-suffixed ebuilds are simply ignored by
60 the package managers.
61
62
63 Specification
64 =============
65
66 Ebuild filename extension syntax: ``ebuild[-<EAPI>]``, where ``[]`` denotes an
67 optional part, and ``<EAPI>`` is the EAPI of the ebuild.
68
69 Let's call the EAPI included in the ebuild filename the pre-source EAPI, and the
70 EAPI set inside the ebuild the post-source EAPI. Given these two, the final EAPI
71 used by the ebuild can be established by following these steps:
72
73 * If the pre-source EAPI is not set it defaults to 0.
74 * If the pre-source EAPI is not recognised it is returned immediately.
75 * If the post-source EAPI is not set, it defaults to the pre-source EAPI.
76 * post-source EAPI is returned.
77
78 The above process should be only used to generate the metadata cache. Should the
79 pre-source EAPI be unsupported the cache entry cannot be generated.
80
81 Ebuilds with unsupported EAPIs are masked.
82
83 QA tools should consider it an error for both EAPIs to be set explicitly to
84 different values. Package managers may warn, but must use the post-source EAPI
85 in such cases.
86
87 Examples:
88
89 * ``pkg-1.ebuild``, no EAPI set inside the ebuild
90 pre-source EAPI defaults to 0, post-source EAPI defaults to pre-source EAPI.
91 EAPI 0 is used.
92
93 * ``pkg-2.ebuild-1``, no EAPI set inside the ebuild
94 pre-source EAPI is 1, post-source EAPI defaults to pre-source EAPI.
95 EAPI 1 is used.
96
97 * ``pkg-3.ebuild``, ``EAPI="1"``
98 pre-source EAPI defaults to 0, post-source EAPI is 1.
99 EAPI 1 is used.
100
101 * ``pkg-4.ebuild-2``, ``EAPI="1"``
102 pre-source EAPI is 2, post-source EAPI is 1.
103 EAPI 1 is used, but note that one should **never** explicitly set both
104 EAPIs to different values.
105
106 * ``pkg-5.ebuild-2``, no EAPI set inside the ebuild, package manager not supporting EAPI 2
107 pre-source EAPI is 2, post-source EAPI is never checked.
108 ebuild is masked because of the unsupported pre-source EAPI.
109
110 * ``pkg-6.ebuild``, ``EAPI="2"``, package manager not supporting EAPI 2
111 pre-source EAPI defaults to 0, post-source EAPI is 2 (assuming the
112 package manager didn't die when sourcing the ebuild thinking that EAPI 0
113 is used).
114 ebuild is masked because of the unsupported post-source EAPI.
115
116 Note that it is still not permitted to have more than one ebuild with equal
117 category, package name, and version. Although it would have the advantage of
118 allowing authors to provide backwards compatible ebuilds, it would introduce
119 problems too. The first is the requirement to have strict EAPI ordering, the
120 second is ensuring that all the ebuilds for a single category/package-version
121 are equivalent, i.e. installing any of them has exactly the same effect on a
122 given system.
123
124 Application
125 ===========
126
127 Note that the developers should only set the pre-source EAPI. The process
128 described above is only necessary to avoid undefined behaviour in corner cases
129 and to retain backwards compatibility.
130
131 QA tools may warn if the post-source EAPI is set at all, thus helping with the
132 transition to the new format.
133
134 Other ideas
135 ===========
136
137 There were some other solutions proposed on the mailing list:
138
139 * Set the EAPI inside the ebuild in a way that makes it easy to fetch it
140 * Doesn't meet the backward compatibility requirement.
141 * Isn't forward compatible either.
142 * Could be confusing as ebuilds are considered bash scripts and this
143 would impose additional restrictions on the ebuild format.
144
145 * Do the above and change the ebuild extension to ``.ebuild-ng``
146 * Meets the backward compatibility requirement.
147 * Still can be confusing.
148 * Isn't really forward compatible. What would be after ``.ebuild-ng``?
149 ``.ebuild-ng-ng``?
150
151 * Use different subdirectories for different EAPIs, i.e. cat/pkg/eapiX/
152 * Meets both requirements.
153 * Introduces a noticeable performance hit (several more directory reads
154 in an I/O bound operation).
155 * Makes it much harder for maintainers to see what they have.
156
157
158 References
159 ==========
160
161 .. [#GLEP54] GLEP 54, scm package version suffix
162 (http://glep.gentoo.org/glep-0054.html)
163
164 .. [#PortageProblems] Common portage problems
165 (http://www.gentoo.org/proj/en/portage/doc/common-problems.xml)
166
167 Copyright
168 =========
169
170 This document has been placed in the public domain.
171
172 .. vim: set tw=80 fileencoding=utf-8 spell spelllang=en et :

  ViewVC Help
Powered by ViewVC 1.1.20