Re: [PATCH] warnings: Add gl_WARN_COMPLEMENT and gl_WARN_SUPPORTED.

[Bruno Haible]

Simon Josefsson wrote:
> I guess the effort is to document for each warning variable
> the code snippet that triggers it, and discuss whether it is a common
> warning and how useful it is.
> 
> > The reasonable set that I recommend is "-Wall".
> 
> I'd like to be able to add more to that list, to help catch build
> failures on other systems.

Yes, this is a bit of an effort. Just went through the process with gettext.

The list of warnings that I would disable unconditionally would be:

nw="$nw -Wsystem-headers"            # Don't let system headers trigger warnings
nw="$nw -Wtraditional"               # All compilers nowadays support ANSI C
nw="$nw -Waggregate-return"          # All compilers nowadays support ANSI C
nw="$nw -Wundef"                     # All compiler preprocessors support #if 
UNDEF
nw="$nw -Wconversion"                # These warnings usually don't point to 
mistakes.
nw="$nw -Wsign-conversion"           # Likewise.
nw="$nw -Wtraditional-conversion"    # Likewise.
nw="$nw -Wpadded"                    # We don't want to reorder structs for 
minimum size
nw="$nw -Wvla"                       # We use variable length arrays only when 
the compiler supports them
nw="$nw -Wunreachable-code"          # Complains about many uses of strcmp, due 
to glibc headers.
nw="$nw -Wlogical-op"                # Complains about many uses of strchr, due 
to glibc headers.
nw="$nw -Wcast-qual"                 # Removing 'const' is one of the purposes 
of casting pointers.
nw="$nw -Wstrict-prototypes"         # Complains about definitions of functions 
with empty argument list
nw="$nw -Wold-style-definition"      # Likewise.
nw="$nw -Winline"                    # If the compiler does not want to inline 
some functions, so be it.
nw="$nw -Wredundant-decls"           # Produces warnings for bison generated 
code.
nw="$nw -Wswitch-enum"               # Warns even if there is a 'default:' 
clause in the switch.
nw="$nw -Wunsafe-loop-optimizations" # If the compiler cannot optimize a loop, 
so be it.
nw="$nw -Wbad-function-cast"         # Warns even about casts from double to int
nw="$nw -Wwrite-strings"             # It is sometimes useful to use string 
literals in place of 'char *', without needing to cast.
nw="$nw -Wstrict-overflow"           # Yes our code does not rely on signed 
integer overflow behaviour.
nw="$nw -Wpacked"                    # When we ask for packed structures, we 
accept misalignment.
nw="$nw -Wfloat-equal"               # == of floats should be avoided in 
numerical algorithms, but is needed in testsuites.
nw="$nw -Wswitch-default"            # Enforces a coding style different from 
ours.
# Disable pointless, undesired parts of -W.
warnings="$warnings -Wno-unused-parameter" # Ignored parameters are frequent 
when a function implements a given function type.
warnings="$warnings -Wno-empty-body"       # Enforces a coding style different 
from ours.
warnings="$warnings -Wno-sign-compare"     # These warnings usually don't point 
to mistakes.
warnings="$warnings -Wno-type-limits"      # Type limits are system dependent; 
we prefer if over #if

The list of warnings that I would disable normally but use occasionally would 
be:

nw="$nw -Wc++-compat"                # Not all our source files are meant to be 
compilable in C++ mode.
nw="$nw -Wshadow"                    # Enforces a coding style different from 
ours. But it can be useful to enable it occasionally.
nw="$nw -Wmissing-noreturn"          # Only useful when searching for 
optimizations. But it can be useful to enable it occasionally.
nw="$nw -Wformat-nonliteral"         # gnulib uses some computed format strings 
(in argmatch, vasnprintf)
warnings="$warnings -Wno-uninitialized"    # False positives, due to incomplete 
data flow analysis done by gcc.

Bruno