There should be a way to exit from a task with an error message without a traceback

[frol]

I am validating some arguments inside of a task and I want to exit gracefully with an error message.

Digging into the code showed that it only handles invoke.exceptions.Failure in https://github.com/pyinvoke/invoke/blob/master/invoke/cli.py#L432

At this point, I worked around this with the following hack:

import logging

from invoke.exceptions import Failure
from invoke.runner import Result

class ConfigError(Failure):

    def __init__(self, msg):
        logging.error(msg)
        super(ConfigError, self).__init__(
            Result(stdout='', stderr='', exited=1, pty=None)
        )

and then I can

raise ConfigError("my error message")

But I would rather prefer to have a built-in Invoke exception that will just exit with an error and exit code.

[frol]

Today, I have noticed that the master branch has quite a few fixes, but also it has some internal changes, so my workaround will be the following:

import logging

from invoke.exceptions import Failure
from invoke.runners import Result

class ConfigError(Failure):

    def __init__(self, msg):
        logging.error(msg)
        super(ConfigError, self).__init__(
            Result(commands='', stdout='', stderr='', exited=1, pty=None)
        )

[bitprophet]

History: Invoke's predecessor used an abort function which did this; we moved away from that here because encouraging (and using internally) what amounted to sys.exit(message), made it harder to catch non-critical failures when running tasks as library code - everything turned into SystemExit.

So, that's why we started with just raise Failure and such - easier to start with per-failure-case exceptions and then layer catching/logging on top as needed.

That said,

• Having real logging integration is planned for pre-1.0 (see Support full logging to file fabric/fabric#57 which will be made into an Invoke-specific ticket soon most likely)
• Yes, having a useful "just log an error and exit" method is probably still useful - but I wonder what % of the use case is served by literal use of sys.exit? (Disregarding that logging.error(x) isn't always exactly the same as print >>sys.stderr, x, of course)
• Looking closer, your workaround seems like it'd still end in a traceback, you're just adding the log emit to it - correct? The historical use case is the one where you want just an error message and no traceback - which might be distinct from your use case?

[frol]

I agree that both abort and sys.exit are evil, which is why I use an exception in my workaround. My workaround is ugly, but it works for me. It exploits the internals of Invoke which catch Failure exception and does sys.exit(). I could have made a function with logging and sys.exit() instead, but as I have mentioned in the beginning, I think that there should be only one sys.exit() in the program and it is in Invoke cli entry point.

[indera]

abort() also had nice color support https://github.com/fabric/fabric/blob/fa15c4dc5524e24a7016a4f33e1a3bae7f72455d/fabric/utils.py#L29

[bitprophet]

This got obviated by #476 and #481