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Update status of GLEP 55 according to council decision on 2012-05-08.

1 GLEP: 55
2 Title: Use EAPI-suffixed ebuilds (.ebuild-EAPI)
3 Version: $Revision: 1.5 $
4 Last-Modified: $Date: 2009/05/17 20:56:53 $
5 Author: Piotr JaroszyƄski <peper@gentoo.org>
6 Status: Rejected
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 Status
19 ======
20
21 This GLEP was voted down by the Council in its meeting on 2010-08-23.
22 The Council rejected it again in its meeting on 2012-05-08, in favour
23 of parsing the EAPI from the bash assignment statement in ebuilds.
24
25 Abstract
26 ========
27
28 This GLEP proposes usage of EAPI-suffixed file extensions for ebuilds (for
29 example, foo-1.2.3.ebuild-1).
30
31 Problem
32 =======
33
34 The current way of specifying the EAPI in ebuilds is flawed. In order to get the
35 EAPI the package manager needs to source the ebuild, which itself needs the EAPI
36 in the first place. Otherwise it imposes a serious limitation, namely every ebuild,
37 using any of the future EAPIs, will have to be source'able by old package
38 managers and hence there is no way to do any of the following:
39
40 * Change the behaviour of inherit in any way (for example, to extend or change
41 eclass functionality).
42
43 * Add new global scope functions in any sane way.
44
45 * Extend versioning rules in an EAPI - for example, addition of the scm
46 suffix - GLEP54 [#GLEP54]_ or allowing more sensible version formats like
47 ``1-rc1``, ``1-alpha`` etc. to match upstream more closely.
48
49 * Use newer bash features.
50
51
52 Current behaviour
53 =================
54
55 Following subsections show what happens if you introduce any of the mentioned
56 changes in an ebuild and try to install it with portage 2.1.6.13.
57
58 Incompatible change of inherit (e.g. make it look in the package dir too)
59 -------------------------------------------------------------------------
60
61 ``sys-apps/foo-1.ebuild``::
62
63 EAPI="5"
64 inherit "foo"
65
66 DESCRIPTION=""
67 HOMEPAGE=""
68 SRC_URI=""
69 ...
70
71 Result::
72
73 *
74 * ERROR: sys-apps/foo-1 failed.
75 * Call stack:
76 * ebuild.sh, line 1879: Called _source_ebuild
77 * ebuild.sh, line 1818: Called source '/var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild'
78 * foo-1.ebuild, line 6: Called inherit 'foo'
79 * ebuild.sh, line 1218: Called die
80 * The specific snippet of code:
81 * [ ! -e "$location" ] && die "${1}.eclass could not be found by inherit()"
82 * The die message:
83 * foo.eclass could not be found by inherit()
84 *
85 * If you need support, post the topmost build error, and the call stack if relevant.
86 * This ebuild is from an overlay: '/var/lib/gentoo/repositories/peper/'
87 *
88
89 !!! All ebuilds that could satisfy "sys-apps/foo" have been masked.
90 !!! One of the following masked packages is required to complete your request:
91 - sys-apps/foo-1 (masked by: corruption)
92
93 Current portage looks for eclasses only in the ``eclass`` directory of a
94 repository. This results in a fatal error and ebuild being masked by corruption
95 - might be pretty confusing to users.
96
97 New global scope function
98 -------------------------
99
100 ``sys-apps/foo-1.ebuild``::
101
102 EAPI="5"
103 new_global_scope_function "foo"
104
105 DESCRIPTION=""
106 HOMEPAGE=""
107 SRC_URI=""
108 ...
109
110 Result::
111
112 /var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild: line 7: new_global_scope_function: command not found
113
114 !!! All ebuilds that could satisfy "sys-apps/foo" have been masked.
115 !!! One of the following masked packages is required to complete your request:
116 - sys-apps/foo-1 (masked by: EAPI 5)
117
118 The current version of portage supports EAPI '2'. You must upgrade to a
119 newer version of portage before EAPI masked packages can be installed.
120
121 Not that bad as user is advised to upgrade portage.
122
123 New version format
124 ------------------
125
126 ``sys-apps/foo-2-rc1.ebuild``::
127
128 Invalid ebuild name: /var/lib/gentoo/repositories/peper/sys-apps/foo/foo-2-rc1.ebuild
129
130 emerge: there are no ebuilds to satisfy "sys-apps/foo"
131
132 Not the best error message, especially if there are lots of them.
133
134 Use newer bash features
135 -----------------------
136
137 ``|&`` is a new type of redirection added in bash-4. It cannot be used even in
138 local scope as bash still parses the whole ebuild.
139
140 ``sys-apps/foo-1.ebuild``::
141
142 EAPI="5"
143
144 foo() {
145 echo "foo" |& cat
146 }
147
148 Result::
149
150 /var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild: line 8: syntax error near unexpected token `&'
151 /var/lib/gentoo/repositories/peper/sys-apps/foo/foo-1.ebuild: line 8: ` echo "foo" |& cat'
152 *
153 * ERROR: sys-apps/foo-1 failed.
154 * Call stack:
155 * ebuild.sh, line 1879: Called _source_ebuild
156 * ebuild.sh, line 1818: Called die
157 * The specific snippet of code:
158 * source "${EBUILD}" || die "error sourcing ebuild"
159 * The die message:
160 * error sourcing ebuild
161 *
162 * If you need support, post the topmost build error, and the call stack if relevant.
163 * This ebuild is from an overlay: '/var/lib/gentoo/repositories/peper/'
164 * ... done!
165
166 !!! All ebuilds that could satisfy "sys-apps/foo" have been masked.
167 !!! One of the following masked packages is required to complete your request:
168 - sys-apps/foo-1 (masked by: corruption)
169
170 Again, not the best error.
171
172 Abstract solution
173 =================
174
175 A solution to this problem has to lift those limitations and the only way to do
176 it is to make the EAPI of an ebuild available to the package managers in a way
177 that doesn't require them to source the ebuild. Another important requirement is
178 for the solution to be backward compatible, which has the pleasant side-effect
179 of making the solution applicable in the Gentoo tree right away. Opposed to
180 waiting an arbitrary amount of time, which is never long enough anyway, as the
181 issues listed on the common portage problems page - [#PortageProblems]_ - show.
182
183 Proposed solution
184 =================
185
186 The proposed solution is to use EAPI-suffixed file extensions for ebuilds. This
187 allows package managers to trivially read the EAPI from the ebuild filename. It
188 is also backwards compatible, because currently ebuilds are recognised by the
189 ``.ebuild`` file extension and hence EAPI-suffixed ebuilds are simply ignored by
190 the package managers.
191
192
193 Specification
194 =============
195
196 Ebuild filename extension syntax: ``ebuild[-<EAPI>]``, where ``[]`` denotes an
197 optional part, and ``<EAPI>`` is the EAPI of the ebuild.
198
199 The EAPI used by the ebuild is the EAPI included in the filename if it is set.
200 Otherwise the EAPI set inside the ebuild is used, which defaults to 0 (this is
201 the current behaviour).
202
203 Ebuilds with unsupported EAPIs are masked.
204
205 It should be considered an error to set the EAPI both in the filename and in the
206 ebuild.
207
208 Examples:
209
210 * ``pkg-1.ebuild``, no EAPI set inside the ebuild
211 EAPI defaults to 0.
212
213 * ``pkg-2.ebuild-1``, no EAPI set inside the ebuild
214 EAPI 1 is used.
215
216 * ``pkg-3.ebuild-1``, ``EAPI="1"``
217 EAPI set in both places - error.
218
219 Note that it is still not permitted to have more than one ebuild with equal
220 category, package name, and version. Although it would have the advantage of
221 allowing authors to provide backwards compatible ebuilds, it would introduce
222 problems too. The first is the requirement to have strict EAPI ordering, the
223 second is ensuring that all the ebuilds for a single category/package-version
224 are equivalent, i.e. installing any of them has exactly the same effect on a
225 given system.
226
227 Also note that it is not a new restriction. It is already possible to illegally
228 have multiple versions with different EAPIs as e.g. ``1.0 == 1.00 == 1.00-r0``
229 and hence you could have ``foo-1.0.ebuild`` with EAPI X and ``foo-1.00.ebuild``
230 with EAPI Y.
231
232 Summary of ideas
233 ================
234
235 EAPI-suffixed ebuilds (proposed solution)
236 -----------------------------------------
237
238 Properties:
239 * Can be used right away: yes
240 * Hurts performance: no
241
242 Some say it is clear and simple, others that it is ugly and unintuitive.
243
244 EAPI in the filename with one-time extension change
245 ---------------------------------------------------
246
247 One of the proposed filename formats:
248 ``<PKG>-<VER>.eapi-<EAPI>.eb``
249
250 Properties:
251 * Can be used right away: yes
252 * Hurts performance: no
253
254 This is equivalent to the proposed solution.
255
256 Some say it is better because the extension is static.
257
258 Easily fetchable EAPI inside the ebuild
259 ---------------------------------------
260
261 Properties:
262 * Can be used right away: no
263 * Hurts performance: yes
264
265 Cannot be used right away as it would trigger the errors shown in Current
266 behaviour section for old package managers.
267
268 Performance decrease comes from the fact that with version format changes in the
269 picture package managers need EAPI to parse the ebuild's version. That means that merely
270 picking the best version of a package requires loading EAPI (from cache or the
271 ebuild) for each available ebuild.
272
273 Here is more or less how the package manager figures out the best available
274 version for a package with N versions available.
275
276 * EAPI in the filename
277
278 * Read the directory containing the package - readdir()
279 * For each ebuild, read its EAPI and using that parse its version - no I/O
280 * Sort the versions - no I/O
281 * Going down from the highest to the lowest version
282
283 * Get the metadata from cache - 2 x stat() + read()
284 * break if the version is visible
285
286 * EAPI in the ebuild
287
288 * Read the directory containing the package - readdir()
289 * For each ebuild load its metadata from cache to get its EAPI - N x (2 x stat() + read())
290 * Sort the versions - no I/O
291 * Going down from the highest to the lowest version
292
293 * (metadata is already loaded) - no I/O
294 * break if the version is visible - no I/O
295
296 The difference is in for how many versions the package manager needs to hit
297 cache. With EAPI in the ebuild it needs to do that for all versions, with EAPI
298 in the filename it depends on versions visibility.
299 For example, package foo has versions 1, 2, 3, 4, 5 and 6. 6 is masked, 5 is
300 ~arch and 1,2,3 and 4 are arch. Say, the user accepts only arch for this
301 package. With EAPI in the filename it will read metadata only for versions
302 6, 5 and 4. With EAPI in the ebuild it needs to load metadata for all versions.
303
304 It's hard to say what's the avarage case, but surely the worst case scenario
305 (when only the lowest version is visible) is uncommon.
306
307 Easily fetchable EAPI inside the ebuild and one-time extension change
308 ---------------------------------------------------------------------
309
310 Properties:
311 * Can be used right away: yes
312 * Hurts performance: yes
313
314 Performance decrease as described in the previous section.
315
316 Some say it is clear and simple, others that it is confusing and unintuitive,
317 because of the arbitrary format restrictions in what is a bash script otherwise.
318
319 Use different subdirectories for different EAPIs, i.e. cat/pkg/eapiX/
320 ---------------------------------------------------------------------
321
322 Properties:
323 * Can be used right away: yes
324 * Hurts performance: yes
325
326 Performance decrease comes from the fact that it adds several more directory
327 reads.
328
329 Some say that it makes it much harder for maintainers to see what they have.
330
331 References
332 ==========
333
334 .. [#GLEP54] GLEP 54, scm package version suffix
335 (http://glep.gentoo.org/glep-0054.html)
336
337 .. [#PortageProblems] Common portage problems
338 (http://www.gentoo.org/proj/en/portage/doc/common-problems.xml)
339
340 Copyright
341 =========
342
343 This document has been placed in the public domain.
344
345 .. vim: set tw=80 fileencoding=utf-8 spell spelllang=en et :

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