Most developers expect that you can easily adjust C++ compiler flags
in a GNU package using CXXFLAGS. With LilyPond, however, this is
quite problematic. Reason is that it internally uses the following
variables to compute the final list of compiler flags (see files
`c++-vars.make` and `aclocal.m4`):
OPTIMIZE = <see configure flags --optimize et al.>
SANITIZE = <see configure flag --enable-ubsan>
CXXFLAGS = $CXXFLAGS \
$OPTIMIZE \
$SANITIZE
EXTRA_CXXFLAGS = -W -Wall -Wconversion
ALL_CXXPPFLAGS = $(CPPFLAGS) \
$(CONFIG_CPPFLAGS) \
$(DEFINES) \
$(INCLUDES:%=-I%)
ALL_CXXFLAGS = $(CXXFLAGS) \
$(ALL_CXXPPFLAGS) \
$($(PACKAGE)_CXXFLAGS) \
$(CONFIG_CXXFLAGS) \
$(MODULE_CXXFLAGS) \
$(EXTRA_CXXFLAGS)
As an example, the quite frequent idiom to disable optimization with
./configure CXXFLAGS="-O0"
fails because $OPTIMIZE overrides this. Similarly, it is not possible
to disable a warning like
./configure CXXFLAGS="-Wno-sign-conversion
since it gets overridden by the `-Wall -W -Wconversion` options in
$EXTRA_CXXFLAGS. Instead, you have to say
make EXTRA_CXXFLAGS="-W -Wall -Wconversion -Wno-sign-conversion"
(completely bypassing the configuring step) to disable sign conversion
warnings.
This is very, very non-standard and completely undocumented.
Any idea how this could be improved?
Werner
