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