Decorator stacking problems and @task

[bitprophet]

Description

This is at least a documentation problem, if not a code one -- using @task "inside" other decorators such as @hosts doesn't work well, and @task must thus come at the top of the decorator 'list'. See this ML thread for details.

See also Erich Heine's post in that thread suggesting a way of normalizing the various decorators so this becomes less of a problem. It sounds a lot like Travis' idea of preemtively wrapping classic-style tasks in class tasks so that we can start assuming Task objects in the rest of the system.

EDIT: I think it makes more sense to defer this to 1.4/1.5 and correctly normalize things, instead of adding a doc/FAQ change that will become obsolete soon after.

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Originally submitted by Jeff Forcier (bitprophet) on 2011-08-11 at 02:32pm EDT

[dcolish]

I'm not seeing issues with stacking order when using the hosts and task decorators. Is there a clear failure case? Its not obvious from the ML thread. Could this have been already fixed inadvertently?

[bitprophet]

It seems to make the tasks not show up as valid tasks, i.e. they're not in --list nor can they be specified on the CLI or called with execute('name').

[dcolish]

Hmm, i didn't have any issues in this trivial example regardless of the order of the decorators. I should not this runs on my branch with dotted path support, but i dont think that is effecting anything here.

@task
@hosts('host1')
@runs_once
def some_task():
    print env['host']

execute(some_task)

[bitprophet]

A) note that I said execute('name') not execute(task_object) ;)
B) If you're calling execute() at top level at all, you're not using fab the tool, which is where the problem comes up.

With the following fabfile.py:

from fabric.api import *

@hosts('localhost')
@task
def foo():
    run("uname -a")

@task
def bar():
    execute('foo')

invoking it as fab --list shows this output:

Available commands:

    bar

Strike one: it's not showing foo. Reversing the order of decorators on foo makes it show up in --list correctly.

Invoking fab bar, which should simply execute 'foo' (via name lookup), results in Fatal error: None is not callable or a valid task name. Strike two. Reversing the order of decorators, again, fixes this. Switching from execute('foo') to execute(foo) (if the decorators are in the "wrong" order) also makes it work fine.

[dcolish]

Ah, I see whats going on here. My example was producing this behavior when I ran from the command line as well. I've traced through what is used to append tasks for listing from the cli. It looks like the application of decorators after task is destroying the type information needed, ie, isinstance(a, Task). I don't have a solution yet, but that's the cause afaik.

[dcolish]

Sorry, github seems to have some way of linking issues I don't understand. I sent pull request #548 to start work on a fix for this.

[bitprophet]

@dcolish I think it just doesn't parse the title/header for "#XXX", I edited your description field to include the reference and it should now show up in here as an autolink commenty looking thingamabob. EDIT: yup.

[bitprophet]

Just realized: the "make all our decorators return Task objects" approach would solve it for the use case of "already buying into new-style tasks" -- but it breaks for anybody using old-style tasks :(

EDIT: Except for the if statements in @dcolish's diff, though. That should handle things OK, unless I was thinking of something else before.

[bitprophet]

As it turns out, this can be implemented in a relatively sane way, and I don't think it does need to be part of 1.4, so I'm going to backport my implementation of it to 1.3.x. That should be pushed soon, then I can do a flight of releases.