AddFilesDynamically

The function presented here is useful if:

• You've got one environment used to create many targets (too many to start messing with).
• The environment is configured differently for different platforms/compilers/etc.
• Some platforms/compilers/etc. need an additional source file to be compiled in order to work properly. This can be, for example, a replacement for a library that is not available on a certain platform. This function wraps a given emitter with another emitter that adds another file to the source nodes.

Replaceable emitters (as of SCons 0.96.90):

• PROGEMITTER - emitter for Program builder
• SHLIBEMITTER - emitter for SharedLibrary builder
• LIBEMITTER - emitter for Library builder

The Function

def add_file_to_emitter(env, emitter_name, file):
    try:
        original_emitter = env[emitter_name]
        if type(original_emitter) == list:
            original_emitter = original_emitter[0]
    except KeyError:
        original_emitter = None

    def emitter(target, source, env):
        if original_emitter:
            target, source = original_emitter(target, source, env)
        return target, source + [file]

    env[emitter_name] = emitter

Example Usage

In this example, the environment is searched for a library called somelib. If this library is not found, add_file_to_emitter is called to add somelibreplacement.c to every program built using the environment.

env = Environment()
conf = env.Configure()
if not conf.CheckLib('somelib'):
  add_file_to_emitter(env, 'PROGEMITTER', File('somelibreplacement.c'))
conf.Finish()

• -- AmirSzekely

Changing the Emitter for StaticObject

If you want to change where a builder finds its C/C++ source files, you want to change the emitter for the StaticObject builder, aka Object. Unfortunately, there is no OBJEMITTER currently defined, but another way to do it is shown below.

# Assuming the BUILD_DIR is set to the location of the generated files
# and some other generated files are in OTHER_BUILD_DIR
def my_emitter(target, source, env):
    """Tell SCons about the locations of some generated files. This could
    be any emitter you want"""
    if os.path.exists(source[0].path):
        # The source file was generated in the local build directory
        return (target, source)
    altSrcName = source[0].abspath.replace(env["BUILD_DIR"] + os.sep, "")
    if os.path.exists(altSrcName):
        # The source file is in the source directory
        return (target, altSrcName)
    # Assume that the source file is in the other generated files build directory
    altSrcName = "%s/%s%s" % (
        File("#"),
        env["OTHER_BUILD_DIR"],
        source[0].path.replace(env["OTHER_BUILD_DIR"], ""),
    )
    return (target, altSrcName)


# This is the part where we override the emitter for the Object builder
from SCons.Tool import createObjBuilders

# Get the underlying builder objects
static_obj, shared_obj = createObjBuilders(env)
# Now SCons can find .cpp files in different locations
static_obj.add_emitter(".cpp", my_emitter)

• -- MattDoar