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<section id="nep-2-a-proposal-to-build-numpy-without-warning-with-a-big-set-of-warning-flags">
<span id="nep02"></span><h1>NEP 2 — A proposal to build numpy without warning with a big set of warning flags<a class="headerlink" href="#nep-2-a-proposal-to-build-numpy-without-warning-with-a-big-set-of-warning-flags" title="Link to this heading">#</a></h1>
<dl class="field-list simple">
<dt class="field-odd">Author<span class="colon">:</span></dt>
<dd class="field-odd"><p>David Cournapeau</p>
</dd>
<dt class="field-even">Contact<span class="colon">:</span></dt>
<dd class="field-even"><p><a class="reference external" href="mailto:david%40ar.media.kyoto-u.ac.jp">david<span>@</span>ar<span>.</span>media<span>.</span>kyoto-u<span>.</span>ac<span>.</span>jp</a></p>
</dd>
<dt class="field-odd">Date<span class="colon">:</span></dt>
<dd class="field-odd"><p>2008-09-04</p>
</dd>
<dt class="field-even">Status<span class="colon">:</span></dt>
<dd class="field-even"><p>Deferred</p>
</dd>
</dl>
<section id="executive-summary">
<h2>Executive summary<a class="headerlink" href="#executive-summary" title="Link to this heading">#</a></h2>
<p>When building numpy and scipy, we are limited to a quite restricted set of
warning compilers, thus missing a large class of potential bugs which could be
detected with stronger warning flags. The goal of this NEP is present the
various methods used to clean the code and implement some policy to make numpy
buildable with a bigger set of warning flags, while keeping the build warnings
free.</p>
</section>
<section id="warning-flags">
<h2>Warning flags<a class="headerlink" href="#warning-flags" title="Link to this heading">#</a></h2>
<p>Each compiler detects a different set of potential errors. The baseline will
be gcc -Wall -W -Wextra. Ideally, a complete set would be nice:</p>
<div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>-W<span class="w"> </span>-Wall<span class="w"> </span>-Wextra<span class="w"> </span>-Wstrict-prototypes<span class="w"> </span>-Wmissing-prototypes<span class="w"> </span>-Waggregate-return
-Wcast-align<span class="w"> </span>-Wcast-qual<span class="w"> </span>-Wnested-externs<span class="w"> </span>-Wshadow<span class="w"> </span>-Wbad-function-cast
-Wwrite-strings<span class="w"> </span><span class="s2">"</span>
</pre></div>
</div>
<p>Intel compiler, VS with <code class="docutils literal notranslate"><span class="pre">/W3</span> <span class="pre">/Wall</span></code>, Sun compilers have extra warnings too.</p>
</section>
<section id="kind-of-warnings">
<h2>Kind of warnings<a class="headerlink" href="#kind-of-warnings" title="Link to this heading">#</a></h2>
<p>C Python extension code tends to naturally generate a lot of spurious warnings.
The goal is to have some facilities to tag some typical C-Python code so that
the compilers do not generate warnings in those cases; the tag process has to
be clean, readable, and be robust. In particular, it should not make the code
more obscure or worse, break working code.</p>
<section id="unused-parameter">
<h3>Unused parameter<a class="headerlink" href="#unused-parameter" title="Link to this heading">#</a></h3>
<p>This one appears often: any python-callable C function takes two arguments,
of which the first is not used for functions (only for methods). One way to
solve it is to tag the function argument with a macro NPY_UNUSED. This macro
uses compiler specific code to tag the variable, and mangle it such as it is
not possible to use it accidentally once it is tagged.</p>
<p>The code to apply compiler specific option could be:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#if defined(__GNUC__)</span>
<span class="w"> </span><span class="cp">#define __COMP_NPY_UNUSED __attribute__ ((__unused__))</span>
<span class="cp"># elif defined(__ICC)</span>
<span class="w"> </span><span class="cp">#define __COMP_NPY_UNUSED __attribute__ ((__unused__))</span>
<span class="cp">#else</span>
<span class="w"> </span><span class="cp">#define __COMP_NPY_UNUSED</span>
<span class="cp">#endif</span>
</pre></div>
</div>
<p>The variable mangling would be:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#define NPY_UNUSED(x) (__NPY_UNUSED_TAGGED ## x) __COMP_NPY_UNUSED</span>
</pre></div>
</div>
<p>When applied to a variable, one would get:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="n">foo</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">NPY_UNUSED</span><span class="p">(</span><span class="n">dummy</span><span class="p">))</span>
</pre></div>
</div>
<p>expanded to:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="n">foo</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">__NPY_UNUSED_TAGGEDdummy</span><span class="w"> </span><span class="n">__COMP_NPY_UNUSED</span><span class="p">)</span>
</pre></div>
</div>
<p>Thus avoiding any accidental use of the variable. The mangling is pure C, and
thus portable. The per-variable warning disabling is compiler specific.</p>
</section>
<section id="signed-unsigned-comparison">
<h3>Signed/unsigned comparison<a class="headerlink" href="#signed-unsigned-comparison" title="Link to this heading">#</a></h3>
<p>More tricky: not always clear what to do</p>
</section>
<section id="half-initialized-structures">
<h3>Half-initialized structures<a class="headerlink" href="#half-initialized-structures" title="Link to this heading">#</a></h3>
<p>Just put the elements with NULL in it.</p>
</section>
</section>
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