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  <div class="section" id="other-metadata-variables">
<h1>Other metadata variables<a class="headerlink" href="#other-metadata-variables" title="Permalink to this headline"></a></h1>
<span class="target" id="index-0"></span><div class="section" id="dynamic-slots-multislot-flag">
<span id="index-1"></span><h2>Dynamic slots (multislot flag)<a class="headerlink" href="#dynamic-slots-multislot-flag" title="Permalink to this headline"></a></h2>
<dl class="field-list simple">
<dt class="field-odd">Source</dt>
<dd class="field-odd"><p>QA (inferred from PMS)</p>
</dd>
<dt class="field-even">Reference</dt>
<dd class="field-even"><p><a class="reference external" href="https://wiki.gentoo.org/index.php?title=Project:Quality_Assurance/Policies&amp;oldid=109991#multislot.2FUSE-dependent_SLOT">https://wiki.gentoo.org/index.php?title=Project:Quality_Assurance/Policies&amp;oldid=109991#multislot.2FUSE-dependent_SLOT</a></p>
</dd>
<dt class="field-odd">Reported</dt>
<dd class="field-odd"><p><code class="docutils literal notranslate"><span class="pre">use</span></code> in global scope triggers fatal error</p>
</dd>
</dl>
<p>The use of <code class="docutils literal notranslate"><span class="pre">multislot</span></code> to alter <code class="docutils literal notranslate"><span class="pre">SLOT</span></code> values (as well as any other
USE-dependent slot values) in the Gentoo repository is forbidden.
Such a feature can be used in overlays, and it is acceptable to provide
such support in eclasses as long as it is not used in ::gentoo.</p>
<p>This policy has been explicitly declared in response to historical
(pre-2016) use of <code class="docutils literal notranslate"><span class="pre">USE=multislot</span></code> in toolchain ebuilds.  When the flag
was disabled, all package versions used the same slot, and upgrades were
handled as for non-slotted packages.  When the flag was enabled, each
version used a separate slot, permitting multiple versions being
installed simultaneously.  This allowed the user to choose between
the two options.</p>
<p>The original violation has been resolved by unconditionally slotting
the packages.  This permitted the users to install multiple versions
in parallel, while removal of old versions was to be handled via
<code class="docutils literal notranslate"><span class="pre">emerge</span> <span class="pre">--depclean</span></code>.</p>
<p><em>Rationale</em>: this feature was in direct violation of PMS <a class="reference external" href="https://projects.gentoo.org/pms/7/pms.html#x1-600007.1">metadata
invariance</a> requirements.  It caused the cached slot value to depend
on the state of querying the USE flag (which in turn could technically
depend on slot, via <code class="docutils literal notranslate"><span class="pre">package.use</span></code>).  This caused undefined package
manager behavior which could include use of unpredictable slot, cache
invalidation or explicit errors.</p>
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<li class="toctree-l1 current"><a class="current reference internal" href="#">Other metadata variables</a><ul class='nav'>
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