We have around 60 repos using the 'mccabe' package to do cyclomatic
complexity checks in flake8 in their gate jobs.[1] Based on advice
received at the time[2], the version of mccabe that we use in the gate
is effectively pinned to 0.2.1 by hacking (the project, not... never
mind).[3]
This is starting to cause problems, because version 0.2.1 does not work
with Python 3. By 'does not work' I don't mean that it refuses to run, I
mean that it returns completely different numbers. (As far as I can tell
they're always the same or lower.) tox creates the pep8 environment
using the version of python that tox itself is running in, so as distros
increasingly prefer to install packages using python3, people will
increasingly be running flake8 under python3, and they'll run into
situations like the one I had today where their pep8 tests pass locally
but fail in the gate (which still runs under python2). When the gate
switches to python3, as I assume it eventually must, we'll get bogus
results.
Unfortunately, moving to a later version is complicated by the fact that
0.2.1 was... not good software. There is exactly one regression test.[4]
And if you're about to ask whether it was to check the trivial case that
the function:
def foo():
return None
has a cyclomatic complexity of 1, then the joke is on you because it
actually returns 2 for that function.
Later versions have more tests and appear to be consistent with each
other and across python versions, but they return completely different
results to 0.2.1. And the results are mostly higher, so if we bump the
requirements many of those 60 projects will break.
(I could also go into details on how the numbers that later versions
report are also wrong in different ways, but I'll save it for another day.)
Here's how the allegedly most complex function in Heat[5] shakes out,
for example:
mccabe py27 py36
0.2.1 14 6
0.3.1 23 23
0.6.1 23 23
I don't have a solution to suggest, but I burned most of my day digging
into this so I just wanted to let y'all know how screwed we are.
cheers,
Zane.
[1]
https://github.com/search?q=org%3Aopenstack+max-complexity+extension%3A.ini+path%3A%2F&type=Code
[2]
http://lists.openstack.org/pipermail/openstack-dev/2014-October/048701.html
[3]
http://git.openstack.org/cgit/openstack-dev/hacking/tree/requirements.txt#n9
[4] https://github.com/PyCQA/mccabe/blob/0.2.1/test_mccabe.py
[5]
http://git.openstack.org/cgit/openstack/heat/tree/heat/engine/scheduler.py#n299
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