Scons LIBS linking, how to remove duplicate LIBS? - scons

Question

We use indirection when specifying library dependencies, for instance,
env.Program(TARGET, SOURCE, LIBS = [ $LIBS_A, $LIBS_B, $LIBS_C ])
LIBS_A, LIBS_B, and LIBS_C are specified in other SConscript files.
Suppose:
LIBS_A/Sconscript has LIBS_A = [ foo, bar, baz ]
LIBS_B/Sconscript has LIBS_B = [ foo, bar, bat ]
LIBS_C/Sconscript has LIBS_C = [ foo, bar, ben ]
Then the final linker line will have:
-lfoo -lbar -lbaz -lfoo -lbar -lbat -lfoo -lbar -lben
How can we remove duplicates and have the linker line read:
-lfoo -lbar -lbaz -lbat -lben

Answer 1

How's this. files fully listed.
main.cxx
#include <iostream>
int main()
{
std::cout << "Hello World!";
}
SConstruct
env=Environment()
Export('env')
for l in ['A','B','C']:
env.SConscript("LIBS_%s/SConscript"%l)
env.Program('myprogram',['main.cxx'], LIBS = list(set(env['LIBS_A'] + env['LIBS_B'] + env['LIBS_C'])))
LIBS_A/SConscript
Import('env')
env['LIBS_A'] = ['foo','bar','baz']
LIBS_B/SConscript
Import('env')
env['LIBS_B'] = ['foo','bar','bat']
LIBS_C/SConscript
Import('env')
env['LIBS_C'] = ['foo','bar','ben']
Yields:
g++ -o myprogram main.o -lbaz -lbat -lfoo -lbar -lben
If none of those would work for you, here's a more complicated way that should:
class foo(object):
def __init__(self, arg):
self.arg = arg
def __call__(self, target, source, env, for_signature):
print "LIBS_A: %s LIBS_B: %s"%(env['LIBS_A'],env['LIBS_B'])
rc = list(set(env['LIBS_A']+env['LIBS_B']))
print "Unique: %s"%rc
print "SIG:%s"%for_signature
return rc
# Will call our foo method to uniquify LIBS_*
env=Environment(FOO=foo, BAR="${FOO('$LIBS_A $LIBS_B')}")
env.Command('foo.XXXXX','foo.in',action="echo LIBS: $LIBS",LIBS="$BAR",
LIBS_A=['a','b','c','d','e','f','f','b'],
LIBS_B=['b','d','e','g','x'])

Answer 2

This worked for me. Big thanks to #bdbaddog
class uniquify_libs(object):
def __init__(self, arg):
self.arg = arg
def __call__(self, target, source, env, for_signature):
rc = list(set(env.subst(env[self.arg])[0].split()))
return rc
LIBS = ['$LIBS_A', '$LIBS_B'] ## defined in other SConscripts
Program(
target = TARGET,
source = SOURCE,
UNIQUE = uniquify_libs,
MYLIBS = LIBS,
LIBS = "${UNIQUE('MYLIBS')}",
)