using scons for literate programming - scons

Question

Using noweb, I would either like to generate a document file (or a source file) from a noweb input file **.nw
From hand I would do something like that:
notangle my_program.nw > my_program.cpp
g++ -c my_program.o my_program.cpp
ln -o myapp ... my_program.o ...
Now I like to ask whether I can use scons to automate this.
Imagine, my project directory is on $MYPROJECT. THere we have "$MYPROJECT/SConstruct".
Now I defined a scons tool "tangle.py" (simplified from "noweb.py).
Here we have "$MYPROJECT/site_scons/site_tools/tangle.py"
import SCons.Builder
def cpp_emit (target,source, env):
# I dont know what to do here ... please help
return (target,source)
# Tangle to .cpp
__noweb_tangle_builder = SCons.Builder.Builder(
action='/usr/bin/notangle $SOURCES >$TARGET',
suffix='.cpp',
src_suffix='.nw',
emitter=cpp_emit)
# -----------------------
def generate(env):
env['BUILDERS']['tangle']= __noweb_tangle_builder
def exists(env):
return 1
This tool generates a cpp-file from a nw-file.
But if I do something like
def cpp_emit (target,source, env):
new_source=target[0].name
new_target=new_source.rstrip(".cpp")+".o"
target.append(new_target)
source.append(new_source)
return (target, source)
I get into a dependency circle. SCons will find and abort with an error message.
Doing ...
def cpp_emit (target,source, env):
new_source=target[0].name
# someprogram.cpp -> someprogram.o
new_target=new_source.rstrip(".cpp")+".o"
# lets avoid dependency cycle
t = []
t.append(new_target)
source.append(new_source)
# oops, we dropped target test.cpp. It wont be generated.
return (t, source)
... the tool would stop generating a cpp file from a nw file. (Cpp target dropped)
Do you know a working way to do use scons for literate programming?
thank you for reading.
Leonard

Answer 1

Here is the tool that I created. Note the use of env['BUILDERS']['Object'].src_builder to allow env.Program() to accept noweb files.
# site_cons/site_tools/tangle.py
import SCons.Builder
__all__=['generate', 'exists']
tangle_builder = SCons.Builder.Builder(
action='$NOTANGLE $SOURCES > $TARGET',
suffix = '.cpp',
src_suffix = '.nw')
def generate(env):
env['NOTANGLE'] = exists(env)
env['BUILDERS']['Tangle'] = tangle_builder
if 'Object' in env['BUILDERS']:
env['BUILDERS']['Object'].src_builder.append('Tangle')
def exists(env):
if 'NOTANGLE' in env:
return env['NOTANGLE']
return env.WhereIs('notangle')
And its use:
# SConstruct
env = Environment(tools=['default', 'tangle'])
env.Program('my_program.nw')
Here is the output of the above SConstruct:
$ scons -Q
/usr/bin/notangle my_program.nw > my_program.cpp
g++ -o my_program.o -c my_program.cpp
g++ -o my_program my_program.o
$ scons -c
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Cleaning targets ...
Removed my_program.cpp
Removed my_program.o
Removed my_program
scons: done cleaning targets.

Answer 2

Seems like you're trying to add the object file without actually compiling the cpp file.
I made a small example that should help clear up the situation. Basically, since you configured the suffix, and src_suffix in the call to Builder, the sources and targets are correctly setup by SCons, and you dont need the emitter.
def cpp_emit (target,source, env):
for t in target:
print 'Emitter target: %s' % (t)
for s in source:
print 'Emitter source: %s' % (s.name)
return (target,source)
# Tangle to .cpp
builder = Builder(
action='/home/notroot/projects/sandbox/Emitter/builder.sh $SOURCES $TARGET',
suffix='.cc',
src_suffix='.nw',
emitter=cpp_emit)
env = Environment()
env['BUILDERS']['tangle'] = builder
tangleTarget = env.tangle(target='main.cc', source='main.nw')
env.Object(source=tangleTarget)
And here is the output:
$ scons
scons: Reading SConscript files ...
Emitter target: main.cc
Emitter source: main.nw
scons: done reading SConscript files.
scons: Building targets ...
/home/notroot/projects/sandbox/Emitter/builder.sh main.nw main.cc
g++ -o main.o -c main.cc
scons: done building targets.
$ scons -c
scons: Reading SConscript files ...
Emitter target: main.cc
Emitter source: main.nw
scons: done reading SConscript files.
scons: Cleaning targets ...
Removed main.cc
Removed main.o
scons: done cleaning targets.
I did the following to get the Builder to generate the cc file and compile it, but it doesnt clean the object file.
import os
def cpp_emit(target,source, env):
for s in source:
print 'Emitter source: %s' % (s.name)
for t in target:
print 'Emitter target: %s' % (t)
return (target,source)
def build_function(target, source, env):
# Code to build "target" from "source"
for t in target:
print 'Builder target: %s' % (t.name)
for s in source:
print 'Builder source: %s' % (s.name)
buildStr='/home/notroot/projects/sandbox/Emitter/builder.sh %s %s' % (source[0].name, target[0].name)
os.system(buildStr)
trgt = env.Object(source=target[0])
# return 0 or None upon success
return None
# Tangle to .cc and .o
builder = Builder(
action=build_function,
suffix='.cc',
src_suffix='.nw',
emitter=cpp_emit)
env = Environment()
env['BUILDERS']['tangle'] = builder
tangleTarget = env.tangle(target='main.cc', source='main.nw')
Here is the output:
$ scons
scons: Reading SConscript files ...
Emitter source: main.nw
Emitter target: main.cc
scons: done reading SConscript files.
scons: Building targets ...
build_function(["main.cc"], ["main.nw"])
Builder target: main.cc
Builder source: main.nw
scons: done building targets.
$ scons -c
scons: Reading SConscript files ...
Emitter source: main.nw
Emitter target: main.cc
scons: done reading SConscript files.
scons: Cleaning targets ...
Removed main.cc
scons: done cleaning targets.
In this second example, if you add the object file as a target, you will get the following error (rightly so)
scons: *** [main.cc] Multiple ways to build the same target were specified for: main.o (from ['main.nw'] and from ['main.cc'])