Ben Pfaff <b...@cs.stanford.edu> writes:
> Simon Josefsson <si...@josefsson.org> writes:
>
>> Bruno Haible <br...@clisp.org> writes:
>>
>>> Jim Meyering wrote:
>>>> -W
>> ...
>>>> -Wwrite-strings
>>>> -fdiagnostics-show-option
>>>
>>> Thanks. I've updated my build script to include these for glibc/x86 builds
>>> (except -Werror, which causes a configuration error already in
>>> "checking whether the compiler works...").
>>
>> I recommend putting warning flags in a separate variable,
>> e.g. WARN_CFLAGS, which is not used during ./configure checks but only
>> when building (parts of) the project code. That way, -Werror can be
>> used, which I find helpful since I can mentally ignore the compilation
>> output since I know I will be interrupted if there is anything real to
>> pay attention to.
>
> Another approach is to add -Werror last (this is what Eric Blake
> suggested on the autoconf mailing list a long time ago), e.g.:
>
> AC_DEFUN([OVS_ENABLE_WERROR],
> [AC_ARG_ENABLE(
> [Werror],
> [AC_HELP_STRING([--enable-Werror], [Add -Werror to CFLAGS])],
> [], [enable_Werror=no])
> AC_CONFIG_COMMANDS_PRE(
> [if test "X$enable_Werror" = Xyes; then
> CFLAGS="$CFLAGS -Werror"
> fi])])
But does that really work? Don't you risk affecting ./configure checks
that often are written in a way that triggers warnings, and with the
-Werror flag, leads to compilation errors. If the only reason for the
compilation to fail was the -Werror flag, then that ./configure check
has the wrong result. I guess it may depend on where in the ./configure
run the statement above is placed, but that seems fragile to me.
A combination of the two approaches that I've used is this:
if test "$gl_gcc_warnings" = yes; then
gl_WARN_ADD([-Werror], [WERROR_CFLAGS])
gl_WARN_ADD([-Wframe-larger-than=112], [WSTACK_CFLAGS])
nw="$nw -Wsystem-headers" # Don't let system headers trigger warnings
nw="$nw -Wpadded" # Struct in src/idn_cmd.h is not padded
nw="$nw -Wformat" # Self tests and examples print size_t as %d
nw="$nw -Wc++-compat" # We don't care strongly about C++ compilers
nw="$nw -Woverlength-strings" # Some of our strings are too large
nw="$nw -Wsign-conversion" # Too many warnings for now
nw="$nw -Wconversion" # Too many warnings for now
nw="$nw -Wtraditional" # Warns on #elif which we use often
nw="$nw -Wtraditional-conversion" # Too many warnings for now
nw="$nw -Wmissing-noreturn" # Too many warnings for now
nw="$nw -Wunreachable-code" # Too many false positives
nw="$nw -Wlogical-op" # Too many false positives
gl_MANYWARN_ALL_GCC([ws])
gl_MANYWARN_COMPLEMENT(ws, [$ws], [$nw])
for w in $ws; do
gl_WARN_ADD([$w])
done
gl_WARN_ADD([-Wno-format])
gl_WARN_ADD([-Wno-missing-field-initializers])
gl_WARN_ADD([-fdiagnostics-show-option])
fi
note the different variables, WERROR_CFLAGS, WSTACK_CFLAGS and
WARN_CFLAGS. Then I can use $(WERROR_CFLAGS) $(WARN_CFLAGS)
$(WSTACK_CFLAGS) on my own code, and typically $(WARN_CFLAGS) on gnulib
code or similar.
/Simon
