I want to build a library with automake
But the library objects come from two parts
say A_SOURCES and B_SOURCES
and the compilation options for A are different from B

If I use
lib_LIBRARIES = mylib.a
then if I have
mylib_a_SOURCES = list of files for A and B
they will be all compiled with the same options

I want to have something like
lib_LIBRARIES = mylib.a

mylib_a_OBJS = $(A_OBJS) $(B_OBJS)

A_SOURCES = a_list
A_CPPFLAGS = FLAGS_FOR_A

B_SOURCES = b_list
B_CPPFALGS = FLAGS_FOR_B

How to do this ?

I have found a solution myself:

lib_LIBRARIES= mylib.a

then declare the library with only the A subset
mylib_a_SOURCES = A_list
mylib_a_CXXFLAGS = A_FLAGS

then declare a second library not installed
noinst_LIBRARIES = libB.a
with its own sources and compile options
libB_a_SOURCES= B-list
libB_a_CXXFLAGS = B_FLAGS

then simply add one line

mylib_a_LIBADD = libB.a

automake will generate the Makefile that will compile
the A objects then compile the B objects,
build the B library and then it will include B
to build mylib and call ranlib.