SCons and dependencies for python function generating source

Question

edit Totally rewritten example, the issue is the same.

I have SConsctruct file:

env = Environment()

def write_main( out ):
    out.write("""
              #include <iostream>

              int main(int argc, char **argv)
              {{
                std::cout << "[{0}]" << std::endl;
                return 0;
              }}

              \n""".format(ARGUMENTS.get('print', 'nothing'))
            )

def generate_main(env, target, source):
    with open( env.GetBuildPath( target[0] ), 'w') as out:
        write_main( out )

main_builder = env.Builder( action = generate_main )
main_cpp = main_builder( env, env.GetBuildPath('main.cpp'), [] )

prog = env.Program( target='main', source=main_cpp )

Now if I run:

$ scons print=one && ./main 
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
generate_main(["main.cpp"], [])
g++ -o main.o -c main.cpp
g++ -o main main.o
scons: done building targets.
[one]

$ scons print=two && ./main
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
scons: `.' is up to date.
scons: done building targets.
[one]

$ rm main.cpp
$ scons print=two && ./main
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
generate_main(["main.cpp"], [])
g++ -o main.o -c main.cpp
g++ -o main main.o
scons: done building targets.
[two]

So you can clearly see that the middle build was incorrect. How can this be solved?

note: If I move body of write_main to generate_main (so I have only one function) it rebuilds correctly.

note:

One solution I can think of is providing all functions with target object so they can call Depends explicitly. In that example that would mean calling something like:

Depends( target, env.Variable( ARGUMENTS.get('print', 'nothing') ) )

Is there any other approach which would allow me to maintain current signature of write_main without requiring any knowledge about it in generate_main?

And how do I enforce particular syntax highlighting for a piece of code? (in above shell output gets weird/incorrect colors)

Answer 1

You can create explicit dependencies in SCons using the Depends() function.