Call function inside SCons Builder's action - scons

Question

I'm trying to write a Builder in SCons to call a command line executable with some arguments that are generated by a (series of) python functions.
cmdVars = Variables(None, ARGUMENTS)
cmdVars.AddVariables(
EnumVariable('DEBUG', 'help for debug', 'a', allowed_values=('a','b','c')),
PathVariable('CLI', 'path to cli exe', 'C:\...\blah.exe', PathVariable.PathIsFile)
)
env = Environment(variables = cmdVars)
def generateSomeExtraBitsDependingOnFlag(debug):
if (debug == 'a'):
return "-DDEBUG -DBlah myTextHere"
return ''
myBuilder = Builder(
action = '"$CLI" generateSomeExtraBitsDependingOnFlag("$DEBUG")'
)
<extra stuff to add myBuilder to env and call env.myBuilder>
The "$CLI" input is correctly substituted to output (when calling scons) something like C:\Program Files\...\blah.exe but the output from the function never appears, regardless of the DEBUG setting.
Prepending print(debug) inside the function prints $DEBUG whilst parsing the SConstruct file (so it's not surprising it doesn't match the if condition).
Do I just need to use a Generator or follow the instructions in chapter 18.4 (Builders That Execute Python Functions) to make this work? Is the section Writing Builders That Execute External Commands not what I want here?
I suspect that given understanding, the user guide is clear, but without already knowing the answer, the guide is a little opaque to me.

Answer 1

Try this:
cmdVars = Variables(None, ARGUMENTS)
cmdVars.AddVariables(
EnumVariable('DEBUG', 'help for debug', 'a', allowed_values=('a','b','c')),
PathVariable('CLI', 'path to cli exe', 'C:\...\blah.exe', PathVariable.PathIsFile)
)
env = Environment(variables = cmdVars)
def generateSomeExtraBitsDependingOnFlag(source, target, env, for_signature):
if (env['DEBUG'] == 'a'):
return "-DDEBUG -DBlah myTextHere"
return ''
env['generateSomeExtraBitsDependingOnFlag'] =generateSomeExtraBitsDependingOnFlag
myBuilder = env.Builder(
action = '"$CLI" ${generateSomeExtraBitsDependingOnFlag}'
)
env.Append(BUILDERS = {'myBuilder' : myBuilder})
env.myBuilder('dummy','input')