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<section id="migration-guides">
<h1>Migration guides<a class="headerlink" href="#migration-guides" title="Permalink to this heading">¶</a></h1>
<section id="migrating-from-old-python-usedep-syntax-in-python-single-r1">
<span id="index-0"></span><h2>Migrating from old PYTHON_USEDEP syntax in python-single-r1<a class="headerlink" href="#migrating-from-old-python-usedep-syntax-in-python-single-r1" title="Permalink to this heading">¶</a></h2>
<p>Prior to February 2020, <code class="docutils literal notranslate"><span class="pre">python-single-r1</span></code> used to provide a single
<code class="docutils literal notranslate"><span class="pre">PYTHON_USEDEP</span></code> variable alike the two other eclasses. However,
getting it to work correctly both on single-impl and multi-impl packages
required a gross hack.</p>
<p>The current eclass API requires using <code class="docutils literal notranslate"><span class="pre">python_gen_cond_dep</span></code> function
to generate multi-impl deps instead, with <code class="docutils literal notranslate"><span class="pre">PYTHON_USEDEP</span></code> serving
as a placeholder. Single-impl deps can be expressed with
<code class="docutils literal notranslate"><span class="pre">PYTHON_SINGLE_USEDEP</span></code> that can be used either as placeholder,
or directly as a variable.</p>
<p>During a transitional period, <code class="docutils literal notranslate"><span class="pre">PYTHON_USEDEP</span></code> was banned entirely
and <code class="docutils literal notranslate"><span class="pre">PYTHON_MULTI_USEDEP</span></code> was used instead. As of EAPI 8,
the opposite is true — <code class="docutils literal notranslate"><span class="pre">PYTHON_USEDEP</span></code> is to be used,
and <code class="docutils literal notranslate"><span class="pre">PYTHON_MULTI_USEDEP</span></code> was removed.</p>
<p>The recommended rule of thumb for migrating old ebuilds is to:</p>
<ol class="arabic simple">
<li><p>Replace all instances of <code class="docutils literal notranslate"><span class="pre">${PYTHON_USEDEP}</span></code> for simple-impl deps
with <code class="docutils literal notranslate"><span class="pre">${PYTHON_SINGLE_USEDEP}</span></code>. If you don’t know the type
of given dep, dependency check (repoman, pkgcheck) will tell you
if you chose wrong.</p></li>
<li><p>Wrap the dependencies using <code class="docutils literal notranslate"><span class="pre">${PYTHON_USEDEP}</span></code> in a single
<code class="docutils literal notranslate"><span class="pre">python_gen_cond_dep</span></code> block (reordering may be desirable).</p></li>
<li><p>Run <code class="docutils literal notranslate"><span class="pre">pkgcheck</span> <span class="pre">scan</span></code> or <code class="docutils literal notranslate"><span class="pre">repoman</span> <span class="pre">full</span></code>. If you get syntax errors,
you probably missed <code class="docutils literal notranslate"><span class="pre">python_gen_cond_dep</span></code> or did not escape
the <code class="docutils literal notranslate"><span class="pre">$</span></code> in placeholder properly. If you get unmatched dependency,
you probably got single-impl vs. multi-impl wrong.</p></li>
</ol>
<p>This way, you can generally convert ebuilds using trial-and-error
method.</p>
</section>
<section id="migrating-from-eapi-7-to-eapi-8">
<span id="index-1"></span><h2>Migrating from EAPI 7 to EAPI 8<a class="headerlink" href="#migrating-from-eapi-7-to-eapi-8" title="Permalink to this heading">¶</a></h2>
<p>EAPI 8 has banned everything that’s been deprecated in EAPI 7, as well
as some other obsolete stuff. The following table lists all banned
things along with their suggested replacements.</p>
<blockquote>
<div><table class="docutils align-default">
<thead>
<tr class="row-odd"><th class="head"><p>Deprecated thing</p></th>
<th class="head"><p>Replacement</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td colspan="2"><p>Private eclass API</p></td>
</tr>
<tr class="row-odd"><td><p>python_export</p></td>
<td><p>python_setup / getters</p></td>
</tr>
<tr class="row-even"><td><p>python_wrapper_setup</p></td>
<td><p>python_setup</p></td>
</tr>
<tr class="row-odd"><td colspan="2"><p>Obsolete API</p></td>
</tr>
<tr class="row-even"><td><p>distutils_install_for_testing
<code class="docutils literal notranslate"><span class="pre">--via-home</span></code></p></td>
<td><p>no argument (<code class="docutils literal notranslate"><span class="pre">--via-root</span></code>)
or <code class="docutils literal notranslate"><span class="pre">--via-venv</span></code></p></td>
</tr>
<tr class="row-odd"><td><p>python_gen_usedep</p></td>
<td><p>python_gen_cond_dep</p></td>
</tr>
<tr class="row-even"><td><p>PYTHON_MULTI_USEDEP</p></td>
<td><p>PYTHON_USEDEP</p></td>
</tr>
<tr class="row-odd"><td colspan="2"><p>mydistutilsargs rename</p></td>
</tr>
<tr class="row-even"><td><p>mydistutilsargs</p></td>
<td><p>DISTUTILS_ARGS</p></td>
</tr>
<tr class="row-odd"><td colspan="2"><p>Post-Python 2 cleanup</p></td>
</tr>
<tr class="row-even"><td><p>python_gen* -2 / python2
/ pypy</p></td>
<td><p>remove entirely</p></td>
</tr>
<tr class="row-odd"><td><p>python_gen* -3</p></td>
<td><p>make unconditional</p></td>
</tr>
<tr class="row-even"><td><p>python_is_python3</p></td>
<td><p>always assume true</p></td>
</tr>
</tbody>
</table>
</div></blockquote>
<p>The changes can be split roughly into four groups: ban of now-private
eclass API, ban of obsolete API functions, mydistutilsargs rename
and bans related to post-Python 2 cleanup.</p>
<p>The private eclass API part involves <code class="docutils literal notranslate"><span class="pre">python_export</span></code>
and <code class="docutils literal notranslate"><span class="pre">python_wrapper_setup</span></code>. Both were deprecated in March 2020,
and they were never covered in this guide. The former was historically
used to get information about the Python interpreter (either the current
<code class="docutils literal notranslate"><span class="pre">${EPYTHON}</span></code> or an arbitrary choice), the latter to create the wrapper
directory containing <code class="docutils literal notranslate"><span class="pre">python</span></code> and other executables.</p>
<p>When the functions were used to establish a Python build environment,
the replacement for both is a single <code class="docutils literal notranslate"><span class="pre">python_setup</span></code> call. When
<code class="docutils literal notranslate"><span class="pre">python_export</span></code> was used to grab additional details about the Python
interpreter, the various <code class="docutils literal notranslate"><span class="pre">python_get*</span></code> functions should be used
instead.</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>src_configure<span class="o">()</span> <span class="o">{</span>
<span class="c1"># ...</span>
<span class="c1"># OLD:</span>
<span class="nb">local</span> PYTHON_INCLUDEDIR PYTHON_LIBPATH
python_export PYTHON_INCLUDEDIR PYTHON_LIBPATH
<span class="nv">mycmakeargs</span><span class="o">+=(</span>
-DPython3_INCLUDE_DIR<span class="o">=</span><span class="s2">"</span><span class="si">${</span><span class="nv">PYTHON_INCLUDEDIR</span><span class="si">}</span><span class="s2">"</span>
-DPython3_LIBRARY<span class="o">=</span><span class="s2">"</span><span class="si">${</span><span class="nv">PYTHON_LIBPATH</span><span class="si">}</span><span class="s2">"</span>
<span class="o">)</span>
<span class="c1"># NEW:</span>
<span class="nv">mycmakeargs</span><span class="o">+=(</span>
-DPython3_INCLUDE_DIR<span class="o">=</span><span class="s2">"</span><span class="k">$(</span>python_get_includedir<span class="k">)</span><span class="s2">"</span>
-DPython3_LIBRARY<span class="o">=</span><span class="s2">"</span><span class="k">$(</span>python_get_library_path<span class="k">)</span><span class="s2">"</span>
<span class="o">)</span>
<span class="o">}</span>
</pre></div>
</div>
<p>The second group involves sundry API that were deprecated earlier.
These are:</p>
<ol class="arabic simple">
<li><p><code class="docutils literal notranslate"><span class="pre">distutils_install_for_testing</span> <span class="pre">--via-home</span></code> layout that stopped
working correctly at some point. The default <code class="docutils literal notranslate"><span class="pre">--via-root</span></code> should
work most of the time, and <code class="docutils literal notranslate"><span class="pre">-via-venv</span></code> replace the remaining cases
for the removed layout.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">python_gen_usedep</span></code> function that was historically used to generate
partial USE dependencies, and was generally combined with
<code class="docutils literal notranslate"><span class="pre">REQUIRED_USE</span></code> to force specific (usually old) Python interpreters
for specific features. This was really ugly. Nowadays, you should
really use <code class="docutils literal notranslate"><span class="pre">python_gen_cond_dep</span></code> instead.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">PYTHON_MULTI_USEDEP</span></code> placeholder that was temporarily used
in python-single-r1 ebuilds. <code class="docutils literal notranslate"><span class="pre">PYTHON_USEDEP</span></code> is equivalent now.</p></li>
</ol>
<p>The third group is a sole rename of <code class="docutils literal notranslate"><span class="pre">mydistutilsargs</span></code> variable.
Since you usually need to pass the same arguments in all phase
functions, this variable was not really used in local scope. It has
been renamed to uppercase <code class="docutils literal notranslate"><span class="pre">DISTUTILS_ARGS</span></code> to follow the common
pattern for global scope variables.</p>
<p>Finally, the fourth group involves banning some of the features that
were specifically used in order to support distinguish between Python 2
and Python 3. This is meant to force cleaning up old cruft from
ebuilds. It comes in three parts:</p>
<ol class="arabic simple">
<li><p>Banning arguments to <code class="docutils literal notranslate"><span class="pre">python_gen*</span></code> that reference Python 2
(e.g. <code class="docutils literal notranslate"><span class="pre">-2</span></code>, <code class="docutils literal notranslate"><span class="pre">python2*</span></code>, <code class="docutils literal notranslate"><span class="pre">python2_7</span></code>, <code class="docutils literal notranslate"><span class="pre">pypy</span></code>). Since Python 2
is no longer supported in the relevant code paths, the relevant calls
should just be removed.</p></li>
<li><p>Banning the <code class="docutils literal notranslate"><span class="pre">-3</span></code> short-hand to <code class="docutils literal notranslate"><span class="pre">python_gen*</span></code>. Since all
supported interpreters are compatible with Python 3 now, the relevant
code should be made unconditional. Note that <code class="docutils literal notranslate"><span class="pre">python3*</span></code> is still
useful, as it distinguishes CPython from PyPy3.</p></li>
<li><p>Banning the <code class="docutils literal notranslate"><span class="pre">python_is_python3</span></code> function. Since the removal
of Python 2 support, it always evaluated to true.</p></li>
</ol>
<p>All the aforementioned replacements are available in all EAPIs.</p>
</section>
<section id="migrating-to-pep-517-builds">
<h2>Migrating to PEP 517 builds<a class="headerlink" href="#migrating-to-pep-517-builds" title="Permalink to this heading">¶</a></h2>
<p>As of January 2022, the <code class="docutils literal notranslate"><span class="pre">distutils-r1</span></code> can use PEP 517 build backends
instead of calling setuptools directly. The new mode is particularly
useful for:</p>
<ul class="simple">
<li><p>packages using flit and poetry, as a better replacement for
the deprecated <code class="docutils literal notranslate"><span class="pre">dev-python/pyproject2setuppy</span></code> hack</p></li>
<li><p>packages using other PEP 517 build systems (such as pdm) that are not
supported in legacy mode at all</p></li>
<li><p>packages using setuptools without <code class="docutils literal notranslate"><span class="pre">setup.py</span></code></p></li>
<li><p>packages using plain distutils, as the mode handles the switch from
deprecated stdlib distutils to the version vendored in setuptools
safely</p></li>
</ul>
<p>The PEP 517 mode provides the test phase with venv-style installed
package tree (alike <code class="docutils literal notranslate"><span class="pre">distutils_install_for_testing</span> <span class="pre">--via-venv</span></code>)
that should make testing more streamlined.</p>
<p>Unfortunately, the new mode can cause issues with customized distutils
and setuptools build systems. It is important to verify the installed
file list after the migration. Packages that require custom configure
phases or passing arguments are not supported at the moment.</p>
<p>For simple packages, the migration consists of:</p>
<ol class="arabic simple">
<li><p>Adding <code class="docutils literal notranslate"><span class="pre">DISTUTILS_USE_PEP517</span></code> above the inherit line. The value
indicates the build system used, e.g. <code class="docutils literal notranslate"><span class="pre">flit</span></code>, <code class="docutils literal notranslate"><span class="pre">poetry</span></code>,
<code class="docutils literal notranslate"><span class="pre">setuptools</span></code> (used also for distutils).</p></li>
<li><p>Removing <code class="docutils literal notranslate"><span class="pre">DISTUTILS_USE_SETUPTOOLS</span></code>. If the previous value was
<code class="docutils literal notranslate"><span class="pre">rdepend</span></code> (and indeed a runtime dependency is required), then
<code class="docutils literal notranslate"><span class="pre">dev-python/setuptools</span></code> needs to be explicitly added to
<code class="docutils literal notranslate"><span class="pre">RDEPEND</span></code>.</p></li>
<li><p>Removing <code class="docutils literal notranslate"><span class="pre">distutils_install_for_testing</span></code> and/or <code class="docutils literal notranslate"><span class="pre">--install</span></code>
option to <code class="docutils literal notranslate"><span class="pre">distutils_enable_tests</span></code>. This should no longer be
necessary and tests should work out of the box.</p></li>
</ol>
</section>
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