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<title>GLEP 55 -- Use EAPI-suffixed ebuilds (.ebuild-EAPI)</title>
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<td class="textlinks" align="left">
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[<b><a href="http://www.gentoo.org/">Gentoo Linux Home</a></b>]
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[<b><a href="http://www.gentoo.org/proj/en/glep">GLEP Index</a></b>]
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[<b><a href="http://www.gentoo.org/proj/en/glep/glep-0055.txt">GLEP Source</a></b>]
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</td></tr></table>
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<table class="rfc2822 docutils field-list" frame="void" rules="none">
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<tbody valign="top">
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<tr class="field"><th class="field-name">GLEP:</th><td class="field-body">55</td>
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</tr>
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<tr class="field"><th class="field-name">Title:</th><td class="field-body">Use EAPI-suffixed ebuilds (.ebuild-EAPI)</td>
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</tr>
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<tr class="field"><th class="field-name">Version:</th><td class="field-body">1.1</td>
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</tr>
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<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>
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</tr>
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<tr class="field"><th class="field-name">Author:</th><td class="field-body">Piotr Jaroszyński <peper at gentoo.org></td>
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</tr>
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<tr class="field"><th class="field-name">Status:</th><td class="field-body">Draft</td>
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</tr>
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<tr class="field"><th class="field-name">Type:</th><td class="field-body">Standards Track</td>
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</tr>
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<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>
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</tr>
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<tr class="field"><th class="field-name">Created:</th><td class="field-body">17-Dec-2007</td>
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</tr>
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<tr class="field"><th class="field-name">Post-History:</th><td class="field-body">17-Dec-2007, 22-Dec-2007</td>
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</tr>
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</tbody>
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</table>
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<hr />
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<div class="contents topic">
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<p class="topic-title first"><a id="contents" name="contents">Contents</a></p>
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<ul class="simple">
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<li><a class="reference" href="#abstract" id="id3" name="id3">Abstract</a></li>
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<li><a class="reference" href="#problem" id="id4" name="id4">Problem</a></li>
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<li><a class="reference" href="#abstract-solution" id="id5" name="id5">Abstract solution</a></li>
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<li><a class="reference" href="#proposed-solution" id="id6" name="id6">Proposed solution</a></li>
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<li><a class="reference" href="#specification" id="id7" name="id7">Specification</a></li>
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<li><a class="reference" href="#application" id="id8" name="id8">Application</a></li>
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<li><a class="reference" href="#other-ideas" id="id9" name="id9">Other ideas</a></li>
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<li><a class="reference" href="#references" id="id10" name="id10">References</a></li>
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<li><a class="reference" href="#copyright" id="id11" name="id11">Copyright</a></li>
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</ul>
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</div>
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<blockquote>
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<p>"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."</p>
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<p class="attribution">—Alexander Pope, An Essay on Criticism</p>
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</blockquote>
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<div class="section">
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<h1><a class="toc-backref" href="#id3" id="abstract" name="abstract">Abstract</a></h1>
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<p>This GLEP proposes usage of EAPI-suffixed file extensions for ebuilds (for
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example, foo-1.2.3.ebuild-1).</p>
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</div>
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<div class="section">
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<h1><a class="toc-backref" href="#id4" id="problem" name="problem">Problem</a></h1>
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<p>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:</p>
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<blockquote>
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<ul class="simple">
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<li>Change the behaviour of inherit in any way (for example, to extend or change
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eclass functionality).</li>
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<li>Add new global scope functions in any sane way.</li>
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<li>Extend versioning rules in an EAPI - for example, addition of the scm
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suffix - GLEP54 <a class="footnote-reference" href="#glep54" id="id1" name="id1">[1]</a>.</li>
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</ul>
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</blockquote>
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</div>
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<div class="section">
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<h1><a class="toc-backref" href="#id5" id="abstract-solution" name="abstract-solution">Abstract solution</a></h1>
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<p>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 - <a class="footnote-reference" href="#portageproblems" id="id2" name="id2">[2]</a> - show.</p>
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</div>
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<div class="section">
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<h1><a class="toc-backref" href="#id6" id="proposed-solution" name="proposed-solution">Proposed solution</a></h1>
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<p>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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<tt class="docutils literal"><span class="pre">.ebuild</span></tt> file extension and hence EAPI-suffixed ebuilds are simply ignored by
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the package managers.</p>
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</div>
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<div class="section">
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<h1><a class="toc-backref" href="#id7" id="specification" name="specification">Specification</a></h1>
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<p>Ebuild filename extension syntax: <tt class="docutils literal"><span class="pre">ebuild[-<EAPI>]</span></tt>, where <tt class="docutils literal"><span class="pre">[]</span></tt> denotes an
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optional part, and <tt class="docutils literal"><span class="pre"><EAPI></span></tt> is the EAPI of the ebuild.</p>
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<p>Let's call the EAPI included in the ebuild filename the pre-source EAPI, and the
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EAPI set inside the ebuild the post-source EAPI. Given these two, the final EAPI
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used by the ebuild can be established by following these steps:</p>
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<blockquote>
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<ul class="simple">
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<li>If the pre-source EAPI is not set it defaults to 0.</li>
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<li>If the pre-source EAPI is not recognised it is returned immediately.</li>
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<li>If the post-source EAPI is not set, it defaults to the pre-source EAPI.</li>
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<li>post-source EAPI is returned.</li>
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</ul>
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</blockquote>
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<p>The above process should be only used to generate the metadata cache. Should the
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pre-source EAPI be unsupported the cache entry cannot be generated.</p>
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<p>Ebuilds with unsupported EAPIs are masked.</p>
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<p>QA tools should consider it an error for both EAPIs to be set explicitly to
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different values. Package managers may warn, but must use the post-source EAPI
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in such cases.</p>
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<p>Examples:</p>
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<blockquote>
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<ul>
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<li><dl class="first docutils">
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<dt><tt class="docutils literal"><span class="pre">pkg-1.ebuild</span></tt>, no EAPI set inside the ebuild</dt>
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<dd><p class="first last">pre-source EAPI defaults to 0, post-source EAPI defaults to pre-source EAPI.
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EAPI 0 is used.</p>
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</dd>
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</dl>
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</li>
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<li><dl class="first docutils">
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<dt><tt class="docutils literal"><span class="pre">pkg-2.ebuild-1</span></tt>, no EAPI set inside the ebuild</dt>
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<dd><p class="first last">pre-source EAPI is 1, post-source EAPI defaults to pre-source EAPI.
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EAPI 1 is used.</p>
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</dd>
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</dl>
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</li>
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<li><dl class="first docutils">
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<dt><tt class="docutils literal"><span class="pre">pkg-3.ebuild</span></tt>, <tt class="docutils literal"><span class="pre">EAPI="1"</span></tt></dt>
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<dd><p class="first last">pre-source EAPI defaults to 0, post-source EAPI is 1.
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EAPI 1 is used.</p>
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</dd>
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</dl>
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</li>
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<li><dl class="first docutils">
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<dt><tt class="docutils literal"><span class="pre">pkg-4.ebuild-2</span></tt>, <tt class="docutils literal"><span class="pre">EAPI="1"</span></tt></dt>
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<dd><p class="first last">pre-source EAPI is 2, post-source EAPI is 1.
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EAPI 1 is used, but note that one should <strong>never</strong> explicitly set both
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EAPIs to different values.</p>
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</dd>
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</dl>
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</li>
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<li><dl class="first docutils">
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<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>
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<dd><p class="first last">pre-source EAPI is 2, post-source EAPI is never checked.
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ebuild is masked because of the unsupported pre-source EAPI.</p>
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</dd>
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</dl>
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</li>
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<li><dl class="first docutils">
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<dt><tt class="docutils literal"><span class="pre">pkg-6.ebuild</span></tt>, <tt class="docutils literal"><span class="pre">EAPI="2"</span></tt>, package manager not supporting EAPI 2</dt>
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<dd><p class="first last">pre-source EAPI defaults to 0, post-source EAPI is 2 (assuming the
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package manager didn't die when sourcing the ebuild thinking that EAPI 0
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is used).
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ebuild is masked because of the unsupported post-source EAPI.</p>
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</dd>
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</dl>
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</li>
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</ul>
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</blockquote>
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<p>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.</p>
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</div>
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<div class="section">
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<h1><a class="toc-backref" href="#id8" id="application" name="application">Application</a></h1>
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<p>Note that the developers should only set the pre-source EAPI. The process
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described above is only necessary to avoid undefined behaviour in corner cases
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and to retain backwards compatibility.</p>
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<p>QA tools may warn if the post-source EAPI is set at all, thus helping with the
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transition to the new format.</p>
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</div>
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<div class="section">
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<h1><a class="toc-backref" href="#id9" id="other-ideas" name="other-ideas">Other ideas</a></h1>
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<p>There were some other solutions proposed on the mailing list:</p>
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<blockquote>
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<ul>
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<li><dl class="first docutils">
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<dt>Set the EAPI inside the ebuild in a way that makes it easy to fetch it</dt>
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<dd><ul class="first last simple">
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<li>Doesn't meet the backward compatibility requirement.</li>
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<li>Isn't forward compatible either.</li>
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<li>Could be confusing as ebuilds are considered bash scripts and this
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would impose additional restrictions on the ebuild format.</li>
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</ul>
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</dd>
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</dl>
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</li>
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<li><dl class="first docutils">
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<dt>Do the above and change the ebuild extension to <tt class="docutils literal"><span class="pre">.ebuild-ng</span></tt></dt>
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<dd><ul class="first last simple">
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<li>Meets the backward compatibility requirement.</li>
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<li>Still can be confusing.</li>
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<li>Isn't really forward compatible. What would be after <tt class="docutils literal"><span class="pre">.ebuild-ng</span></tt>?
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<tt class="docutils literal"><span class="pre">.ebuild-ng-ng</span></tt>?</li>
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</ul>
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</dd>
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</dl>
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</li>
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<li><dl class="first docutils">
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<dt>Use different subdirectories for different EAPIs, i.e. cat/pkg/eapiX/</dt>
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<dd><ul class="first last simple">
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<li>Meets both requirements.</li>
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<li>Introduces a noticeable performance hit (several more directory reads
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in an I/O bound operation).</li>
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<li>Makes it much harder for maintainers to see what they have.</li>
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</ul>
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</dd>
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</dl>
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</li>
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</ul>
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</blockquote>
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</div>
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<div class="section">
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<h1><a class="toc-backref" href="#id10" id="references" name="references">References</a></h1>
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<table class="docutils footnote" frame="void" id="glep54" rules="none">
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<colgroup><col class="label" /><col /></colgroup>
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<tbody valign="top">
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<tr><td class="label"><a class="fn-backref" href="#id1" name="glep54">[1]</a></td><td>GLEP 54, scm package version suffix
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(<a class="reference" href="http://glep.gentoo.org/glep-0054.html">http://glep.gentoo.org/glep-0054.html</a>)</td></tr>
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</tbody>
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</table>
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<table class="docutils footnote" frame="void" id="portageproblems" rules="none">
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<colgroup><col class="label" /><col /></colgroup>
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<tbody valign="top">
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<tr><td class="label"><a class="fn-backref" href="#id2" name="portageproblems">[2]</a></td><td>Common portage problems
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(<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>
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<div class="section">
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<h1><a class="toc-backref" href="#id11" id="copyright" name="copyright">Copyright</a></h1>
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<p>This document has been placed in the public domain.</p>
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<hr class="footer" />
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<a class="reference" href="glep-0055.txt">View document source</a>.
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antarus |
1.2 |
Generated on: 2008-01-06 02:39 UTC.
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peper |
1.1 |
Generated by <a class="reference" href="http://docutils.sourceforge.net/">Docutils</a> from <a class="reference" href="http://docutils.sourceforge.net/rst.html">reStructuredText</a> source.
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