Error on passing task to other task

[Lense]

from invoke import task

@task
def preTask(ctx):
    print("preTask")

@task
def testTask(ctx, otherTask=preTask):
    print("otherTask @ ", otherTask)

spits out

Traceback (most recent call last):
  File "/usr/bin/inv", line 11, in <module>
    sys.exit(program.run())
  File "/usr/lib/python2.7/site-packages/invoke/program.py", line 269, in run
    self._parse(argv)
  File "/usr/lib/python2.7/site-packages/invoke/program.py", line 329, in _parse
    self.parse_tasks()
  File "/usr/lib/python2.7/site-packages/invoke/program.py", line 490, in parse_tasks
    self.parser = Parser(contexts=self.collection.to_contexts())
  File "/usr/lib/python2.7/site-packages/invoke/collection.py", line 325, in to_contexts
    name=primary, aliases=aliases, args=task.get_arguments()
  File "/usr/lib/python2.7/site-packages/invoke/tasks.py", line 205, in get_arguments
    new_arg = Argument(**self.arg_opts(name, default, taken_names))
  File "/usr/lib/python2.7/site-packages/invoke/tasks.py", line 180, in arg_opts
    if default not in (None, NO_DEFAULT):
  File "/usr/lib/python2.7/site-packages/invoke/tasks.py", line 83, in __eq__
    if self.name != other.name:
AttributeError: 'NoneType' object has no attribute 'name'

I was originally doing something really dumb because I didn't understand how invoke worked, but I came across this weird case. Feel free to close this.

[bitprophet]

Huh, interesting, I think this is because the value you're passing in the signature of testTask is another Task object, and the argument examination stuff obviously didn't anticipate that. Thanks for the report!

Perhaps more deeply, __eq__ may not be well implemented for Task objects - it should say "nope, not equal" if the other object is None. 🤔 Ought to be a trivial fix!

[rsxm]

Hi, while testing/researching inspect.Signature for #357, I also came across this issue.

I'm still making my way through the codebase and don't yet fully understand why the eq method fails when a task is passed as an argument, but I've found two solutions that stops it from failing:

1. Add type checking to eq

   if not isinstance(other, (Task, Call)):
       return False
   

2. Return False on None and when 'name' attribute does not exist

if other is None:
    return False

if not getattr(other, 'name', None):
    return False

I suspect 1 is the better solution, but I don't know Invoke well enough to be sure. Either way, this is indeed "Low-hanging Fruit", and I've got a pull request-able branch (with updated tests) for both approaches.

However, I've got a suspicion that this only treats the symptom, and that the real cause is somehow related to the argspec/arg_opts logic.

[rsxm]

I've figured out how to properly debug Invoke tasks and located the root cause. Turns out there is nothing complicated about this issue :-)

Task.arg_opts simply tries to infer the type of the default value, but first it checks to make sure that the default is not None. If the default happens to be a Task instance, this check calls it's eq method, which breaks because it can't deal with anything else besides a Task instance (or more precisely, an object with a 'name' and a 'body' attribute).

I've opened a pull request that fixes this issue for your review.

[bitprophet]

Thanks @jr-minnaar - will look that over when I get to wrapping up 0.12.3.

[kuwv]

#906

[bitprophet]

Rolling into #906 which includes the fix and a changelog entry for this issue.