SCons script that demonstrates the problem with batch building. After creating two dummy file they are correctly built together in one batch. If another build is initiated scons properly detects that no inputs have changed and doesn't build anything (but note that the output is missing mention of two.txt). The bug happens when you change only on…

output

z:\repro> echo Hello > one.txt
z:\repro> echo Hello > two.txt
z:\repro> scons

scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
build_batch(["one.built", "two.built"], ["one.txt", "two.txt"])
There are 2 targets
echo Hello from one.txt > one.built
echo Hello from two.txt > two.built
scons: done building targets.

z:\repro> scons

scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
scons: `one.built' is up to date.
scons: done building targets.


z:\repro> echo Changed > one.txt

scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
build_batch(["one.built", "two.built"], ["one.txt", "two.txt"])
There are 2 targets
echo Hello from one.txt > one.built
echo Hello from two.txt > two.built
scons: done building targets.

SConstruct

env = Environment()
single_builder = Builder(action='echo Hello from $SOURCE > $TARGET', batch_key=True)

def build_batch(target, source, env):
	print "There are %d targets" % len(target)
	for s in zip(source, target):
		env.Execute(env.subst('echo Hello from $SOURCE > $TARGET', source=s[0], target=s[1]))
		
batched_builder = Builder(action=Action(build_batch, batch_key=True, targets='$CHANGED_TARGETS'))
env.Append(BUILDERS={'Batched': batched_builder})
inputs = ['one', 'two']
Default([env.Batched(source=r'%s.txt' % name, target='%s.built' % name) for name in inputs])