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12     <title>GLEP 55 -- Use EAPI-suffixed ebuilds (.ebuild-EAPI)</title>
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27     <table class="rfc2822 docutils field-list" frame="void" rules="none">
28     <col class="field-name" />
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30     <tbody valign="top">
31     <tr class="field"><th class="field-name">GLEP:</th><td class="field-body">55</td>
32     </tr>
33     <tr class="field"><th class="field-name">Title:</th><td class="field-body">Use EAPI-suffixed ebuilds (.ebuild-EAPI)</td>
34     </tr>
35     <tr class="field"><th class="field-name">Version:</th><td class="field-body">1.1</td>
36     </tr>
37     <tr class="field"><th class="field-name">Last-Modified:</th><td class="field-body"><a class="reference" href="http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/proj/en/glep/glep-0055.txt?cvsroot=gentoo">2008/01/05 02:36:35</a></td>
38     </tr>
39     <tr class="field"><th class="field-name">Author:</th><td class="field-body">Piotr JaroszyƄski &lt;peper&#32;&#97;t&#32;gentoo.org&gt;</td>
40     </tr>
41     <tr class="field"><th class="field-name">Status:</th><td class="field-body">Draft</td>
42     </tr>
43     <tr class="field"><th class="field-name">Type:</th><td class="field-body">Standards Track</td>
44     </tr>
45     <tr class="field"><th class="field-name">Content-Type:</th><td class="field-body"><a class="reference" href="glep-0002.html">text/x-rst</a></td>
46     </tr>
47     <tr class="field"><th class="field-name">Created:</th><td class="field-body">17-Dec-2007</td>
48     </tr>
49     <tr class="field"><th class="field-name">Post-History:</th><td class="field-body">17-Dec-2007, 22-Dec-2007</td>
50     </tr>
51     </tbody>
52     </table>
53     <hr />
54     <div class="contents topic">
55     <p class="topic-title first"><a id="contents" name="contents">Contents</a></p>
56     <ul class="simple">
57     <li><a class="reference" href="#abstract" id="id3" name="id3">Abstract</a></li>
58     <li><a class="reference" href="#problem" id="id4" name="id4">Problem</a></li>
59     <li><a class="reference" href="#abstract-solution" id="id5" name="id5">Abstract solution</a></li>
60     <li><a class="reference" href="#proposed-solution" id="id6" name="id6">Proposed solution</a></li>
61     <li><a class="reference" href="#specification" id="id7" name="id7">Specification</a></li>
62     <li><a class="reference" href="#application" id="id8" name="id8">Application</a></li>
63     <li><a class="reference" href="#other-ideas" id="id9" name="id9">Other ideas</a></li>
64     <li><a class="reference" href="#references" id="id10" name="id10">References</a></li>
65     <li><a class="reference" href="#copyright" id="id11" name="id11">Copyright</a></li>
66     </ul>
67     </div>
68     <blockquote>
69     <p>&quot;A little learning is a dangerous thing; drink deep, or taste not the Pierian
70     spring: there shallow draughts intoxicate the brain, and drinking largely
71     sobers us again.&quot;</p>
72     <p class="attribution">&mdash;Alexander Pope, An Essay on Criticism</p>
73     </blockquote>
74     <div class="section">
75     <h1><a class="toc-backref" href="#id3" id="abstract" name="abstract">Abstract</a></h1>
76     <p>This GLEP proposes usage of EAPI-suffixed file extensions for ebuilds (for
77     example, foo-1.2.3.ebuild-1).</p>
78     </div>
79     <div class="section">
80     <h1><a class="toc-backref" href="#id4" id="problem" name="problem">Problem</a></h1>
81     <p>The current way of specifying the EAPI in ebuilds is flawed. In order to get the
82     EAPI the package manager needs to source the ebuild, which itself needs the EAPI
83     in the first place. Otherwise it imposes a serious limitation, namely every ebuild,
84     using any of the future EAPIs, will have to be source'able by old package
85     managers and hence there is no way to:</p>
86     <blockquote>
87     <ul class="simple">
88     <li>Change behaviour of inherit in any way (for example, to extend or change
89     eclass functionality).</li>
90     <li>Add new global scope functions in any sane way.</li>
91     <li>Extend versioning rules in an EAPI - for example, addition of the scm
92     suffix - GLEP54 <a class="footnote-reference" href="#glep54" id="id1" name="id1">[1]</a>.</li>
93     </ul>
94     </blockquote>
95     </div>
96     <div class="section">
97     <h1><a class="toc-backref" href="#id5" id="abstract-solution" name="abstract-solution">Abstract solution</a></h1>
98     <p>A solution to this problem has to lift those limitations and the only way to do
99     it is to make the EAPI of an ebuild available to the package managers in a way
100     that doesn't require them to source the ebuild. Another important requirement is
101     for the solution to be backward compatible, which has the pleasant side-effect
102     of making the solution applicable in the Gentoo tree right away. Opposed to
103     waiting an arbitrary amount of time, which is never long enough anyway, as the
104     issues listed on the common portage problems page - <a class="footnote-reference" href="#portageproblems" id="id2" name="id2">[2]</a> - show.</p>
105     </div>
106     <div class="section">
107     <h1><a class="toc-backref" href="#id6" id="proposed-solution" name="proposed-solution">Proposed solution</a></h1>
108     <p>The proposed solution is to use EAPI-suffixed file extensions for ebuilds. This
109     allows package managers to trivially read the EAPI from the ebuild filename. It
110     is also backward compatible, because currently ebuilds are recognised by the
111     <tt class="docutils literal"><span class="pre">.ebuild</span></tt> file extension and hence EAPI-suffixed ebuilds are simply ignored by
112     the package managers.</p>
113     </div>
114     <div class="section">
115     <h1><a class="toc-backref" href="#id7" id="specification" name="specification">Specification</a></h1>
116     <p>Ebuild filename extension syntax: <tt class="docutils literal"><span class="pre">ebuild[-&lt;EAPI&gt;]</span></tt>, where <tt class="docutils literal"><span class="pre">[]</span></tt> denotes an
117     optional part, and <tt class="docutils literal"><span class="pre">&lt;EAPI&gt;</span></tt> is the EAPI of the ebuild.</p>
118     <p>Let's call the EAPI included in the ebuild filename the pre-source EAPI, and the
119     EAPI set inside the ebuild the post-source EAPI. Given these two, the final EAPI
120     used by the ebuild can be established by following these steps:</p>
121     <blockquote>
122     <ul class="simple">
123     <li>If the pre-source EAPI is not set it defaults to 0.</li>
124     <li>If the pre-source EAPI is not recognised it is returned immediately.</li>
125     <li>If the post-source EAPI is not set, it defaults to the pre-source EAPI.</li>
126     <li>post-source EAPI is returned.</li>
127     </ul>
128     </blockquote>
129     <p>The above process should be only used to generate the metadata cache. Should the
130     pre-source EAPI be unsupported the cache entry cannot be generated.</p>
131     <p>Ebuilds with unsupported EAPIs are masked.</p>
132     <p>QA tools should consider it an error for both EAPIs to be set explicitly to
133     different values. Package managers may warn, but must use the post-source EAPI
134     in such cases.</p>
135     <p>Examples:</p>
136     <blockquote>
137     <ul>
138     <li><dl class="first docutils">
139     <dt><tt class="docutils literal"><span class="pre">pkg-1.ebuild</span></tt>, no EAPI set inside the ebuild</dt>
140     <dd><p class="first last">pre-source EAPI defaults 0, post-source EAPI defaults to pre-source EAPI.
141     EAPI 0 is used.</p>
142     </dd>
143     </dl>
144     </li>
145     <li><dl class="first docutils">
146     <dt><tt class="docutils literal"><span class="pre">pkg-2.ebuild-1</span></tt>, no EAPI set inside the ebuild</dt>
147     <dd><p class="first last">pre-source EAPI is 1, post-source EAPI defaults to pre-source EAPI.
148     EAPI 1 is used.</p>
149     </dd>
150     </dl>
151     </li>
152     <li><dl class="first docutils">
153     <dt><tt class="docutils literal"><span class="pre">pkg-3.ebuild</span></tt>, <tt class="docutils literal"><span class="pre">EAPI=&quot;1&quot;</span></tt></dt>
154     <dd><p class="first last">pre-source EAPI defaults to 0, post-source EAPI is 1.
155     EAPI 1 is used.</p>
156     </dd>
157     </dl>
158     </li>
159     <li><dl class="first docutils">
160     <dt><tt class="docutils literal"><span class="pre">pkg-4.ebuild-2</span></tt>, <tt class="docutils literal"><span class="pre">EAPI=&quot;1&quot;</span></tt></dt>
161     <dd><p class="first last">pre-source EAPI is 2, post-source EAPI is 1.
162     EAPI 1 is used, but note that one should <strong>never</strong> explicitly set both
163     EAPIs to different values.</p>
164     </dd>
165     </dl>
166     </li>
167     <li><dl class="first docutils">
168     <dt><tt class="docutils literal"><span class="pre">pkg-5.ebuild-2</span></tt>, no EAPI set inside the ebuild, package manager not supporting EAPI 2</dt>
169     <dd><p class="first last">pre-source EAPI is 2, post-source EAPI is never checked.
170     ebuild masked because of the unsupported pre-source EAPI.</p>
171     </dd>
172     </dl>
173     </li>
174     <li><dl class="first docutils">
175     <dt><tt class="docutils literal"><span class="pre">pkg-6.ebuild</span></tt>, <tt class="docutils literal"><span class="pre">EAPI=&quot;2&quot;</span></tt>, package manager not supporting EAPI 2</dt>
176     <dd><p class="first last">pre-source EAPI defaults to 0, post-source EAPI is 2 (assuming the
177     package manager didn't die when sourcing the ebuild thinking that EAPI 0
178     is used).
179     ebuild masked because of the unsupported post-source EAPI.</p>
180     </dd>
181     </dl>
182     </li>
183     </ul>
184     </blockquote>
185     <p>Note that it is still not permitted to have more than one ebuild with equal
186     category, package name, and version. Although it would have the advantage of
187     allowing to provide backward compatible ebuilds, it would introduce problems
188     too. The first is the requirement to have strict EAPI ordering, the second is
189     ensuring that all the ebuilds for a single category/package-version are
190     equivalent, i.e. installing any of them has exactly the same effect to the
191     system.</p>
192     </div>
193     <div class="section">
194     <h1><a class="toc-backref" href="#id8" id="application" name="application">Application</a></h1>
195     <p>Note that the developers should only set the pre-source EAPI. The process
196     described above is only necessary to avoid undefined behaviour in corner cases
197     and to retain backwards compatibility.</p>
198     <p>QA tools may warn if the post-source EAPI is set at all, thus helping with the
199     transition to the new format.</p>
200     </div>
201     <div class="section">
202     <h1><a class="toc-backref" href="#id9" id="other-ideas" name="other-ideas">Other ideas</a></h1>
203     <p>There were some other solutions proposed on the mailing list:</p>
204     <blockquote>
205     <ul>
206     <li><dl class="first docutils">
207     <dt>Set the EAPI inside the ebuild in a way that makes it easy to fetch it</dt>
208     <dd><ul class="first last simple">
209     <li>Doesn't meet the backward compatibility requirement.</li>
210     <li>Isn't forward compatible either.</li>
211     <li>Could be confusing as ebuilds, and not without a reason, are
212     considered bash scripts and this would impose additional restrictions.</li>
213     </ul>
214     </dd>
215     </dl>
216     </li>
217     <li><dl class="first docutils">
218     <dt>Do the above and change the ebuild extension to <tt class="docutils literal"><span class="pre">.ebuild-ng</span></tt></dt>
219     <dd><ul class="first last simple">
220     <li>Meets the backward compatibility requirement.</li>
221     <li>Still can be confusing.</li>
222     <li>Isn't really forward compatible. What would be after <tt class="docutils literal"><span class="pre">.ebuild-ng</span></tt>?
223     <tt class="docutils literal"><span class="pre">.ebuild-ng-ng</span></tt>?</li>
224     </ul>
225     </dd>
226     </dl>
227     </li>
228     <li><dl class="first docutils">
229     <dt>Use different subdirectories for different EAPIs, i.e. cat/pkg/eapiX/</dt>
230     <dd><ul class="first last simple">
231     <li>Meets both requirements.</li>
232     <li>Introduces a noticeable performance hit (several more directory reads
233     in an I/O bound operation).</li>
234     <li>Makes it much harder for maintainers to see what they have.</li>
235     </ul>
236     </dd>
237     </dl>
238     </li>
239     </ul>
240     </blockquote>
241     </div>
242     <div class="section">
243     <h1><a class="toc-backref" href="#id10" id="references" name="references">References</a></h1>
244     <table class="docutils footnote" frame="void" id="glep54" rules="none">
245     <colgroup><col class="label" /><col /></colgroup>
246     <tbody valign="top">
247     <tr><td class="label"><a class="fn-backref" href="#id1" name="glep54">[1]</a></td><td>GLEP 54, scm package version suffix
248     (<a class="reference" href="http://glep.gentoo.org/glep-0054.html">http://glep.gentoo.org/glep-0054.html</a>)</td></tr>
249     </tbody>
250     </table>
251     <table class="docutils footnote" frame="void" id="portageproblems" rules="none">
252     <colgroup><col class="label" /><col /></colgroup>
253     <tbody valign="top">
254     <tr><td class="label"><a class="fn-backref" href="#id2" name="portageproblems">[2]</a></td><td>Common portage problems
255     (<a class="reference" href="http://www.gentoo.org/proj/en/portage/doc/common-problems.xml">http://www.gentoo.org/proj/en/portage/doc/common-problems.xml</a>)</td></tr>
256     </tbody>
257     </table>
258     </div>
259     <div class="section">
260     <h1><a class="toc-backref" href="#id11" id="copyright" name="copyright">Copyright</a></h1>
261     <p>This document has been placed in the public domain.</p>
262     <!-- vim: set tw=80 fileencoding=utf-8 spell spelllang=en et : -->
263     </div>
264    
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