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13.19 manywarnings

The manywarnings module allows you to enable as many GCC warnings as possible for your package. The purpose is to protect against introducing new code that triggers warnings that weren’t already triggered by the existing code base.

An example use of the module is as follows:

# Set up the list of the pointless, undesired warnings.
nw="$nw -Wsystem-headers"       # Don't let system headers trigger warnings
nw="$nw -Wundef"                # All compiler preprocessors support #if UNDEF
nw="$nw -Wtraditional"          # All compilers nowadays support ANSI C
nw="$nw -Wconversion"           # These warnings usually don't point to mistakes.
nw="$nw -Wsign-conversion"      # Likewise.
# Enable all GCC warnings not in this list.
gl_MANYWARN_COMPLEMENT([warnings], [$warnings], [$nw])
for w in $warnings; do

This module is meant to be used by developers who are not very experienced regarding the various GCC warning options. In the beginning you will set the list of undesired warnings (‘nw’ in the example above) to empty, and compile the package with all possible warnings enabled. The GCC option -fdiagnostics-show-option, available in GCC 4.1 or newer, helps understanding which warnings originated from which option. Then you will go through the list of warnings. You will likely deactivate warnings that occur often and don’t point to mistakes in the code, by adding them to the ‘nw’ variable, then reconfiguring and recompiling. When warnings point to real mistakes and bugs in the code, you will of course not disable them.

There are also many GCC warning options which usually don’t point to mistakes in the code; these warnings enforce a certain programming style. It is a project management decision whether you want your code to follow any of these styles. Note that some of these programming styles are conflicting. You cannot have them all; you have to choose among them.

When a new version of GCC is released, you can add the new warning options that it introduces into the gl_MANYWARN_ALL_GCC macro (and submit your modification to the Gnulib maintainers :-)), and enjoy the benefits of the new warnings, while adding the undesired ones to the ‘nw’ variable.

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