Setting up SCons to Autolint

Question

I'm using google's cpplint.py to verify source code in my project meets the standards set forth in the Google C++ Style Guide. We use SCons to build so I'd like to automate the process by having SCons first read in all of our .h and .cc files and then run cpplint.py on them, only building a file if it passes. The issues are as follows:

1. In SCons how do I pre-hook the build process? No file should be compiled until it passes linting.
2. cpplint doesn't return an exit code. How do I run a command in SCons and check whether the result matches a regular expression? I.E., how do I get the text being output?
3. The project is large, whatever the solution to #1 and #2 it should run concurrently when the -j option is passed to SCons.
4. I need a whitelist that allows some files to skip the lint check.

Answer 1

One way to do this is to monkey patch the object emitter function, which turns C++ code into linkable object files. There are 2 such emitter functions; one for static objects and one for shared objects. Here is an example that you can copy paste into a SConstruct:

import sys
import SCons.Defaults
import SCons.Builder
OriginalShared = SCons.Defaults.SharedObjectEmitter
OriginalStatic = SCons.Defaults.StaticObjectEmitter

def DoLint(env, source):
    for s in source:
        env.Lint(s.srcnode().path + ".lint", s)

def SharedObjectEmitter(target, source, env):
    DoLint(env, source)
    return OriginalShared(target, source, env)

def StaticObjectEmitter(target, source, env):
    DoLint(env, source)
    return OriginalStatic(target, source, env)

SCons.Defaults.SharedObjectEmitter = SharedObjectEmitter
SCons.Defaults.StaticObjectEmitter = StaticObjectEmitter
linter = SCons.Builder.Builder(
    action=['$PYTHON $LINT $LINT_OPTIONS $SOURCE','date > $TARGET'],
    suffix='.lint',
    src_suffix='.cpp')

# actual build
env = Environment()
env.Append(BUILDERS={'Lint': linter})
env["PYTHON"] = sys.executable
env["LINT"] = "cpplint.py"
env["LINT_OPTIONS"] = ["--filter=-whitespace,+whitespace/tab", "--verbose=3"]
env.Program("test", Glob("*.cpp"))

There's nothing too tricky about it really. You'd set LINT to the path to your cpplint.py copy, and set appropriate LINT_OPTIONS for your project. The only warty bit is creating a TARGET file if the check passes using the command line date program. If you want to be cross platform then that'd have to change.

Adding a whitelist is now just regular Python code, something like:

whitelist = """"
src/legacy_code.cpp
src/by_the_PHB.cpp
"""".split()

def DoLint(env, source):
    for s in source:
        src = s.srcnode().path
        if src not in whitelist:
            env.Lint( + ".lint", s)

It seems cpplint.py does output the correct error status. When there are errors it returns 1, otherwise it returns 0. So there's no extra work to do there. If the lint check fails, it will fail the build.

This solution works with -j, but the C++ files may compile as there are no implicit dependencies between the lint fake output and the object file target. You can add an explicit env.Depends in there to force that the ".lint" output depend on the object target. As is it's probably enough, since the build itself will fail (scons gives a non-zero return code) if there are any remaining lint issues even after all the C++ compiles. For completeness the depends code would be something like this in the DoLint function:

def DoLint(env, source, target):
    for i in range(len(source)):
        s = source[i]
        out = env.Lint(s.srcnode().path + ".lint", s)
        env.Depends(target[i], out)

Answer 2

AddPreAction seems to be what you are looking for, from the manpage:

AddPreAction(target, action)
env.AddPreAction(target, action)
Arranges for the specified action to be performed before the specified target is built. T

Also see http://benno.id.au/blog/2006/08/27/filtergensplint for an example.

Answer 3

See my github for a pair of scons scripts complete with an example source tree. It uses Google's cpplint.py.

https://github.com/xyzisinus/scons-tidbits