Deduplication does not care with post constraint

[presidento]

If a and b tasks has the same pre and post tasks and I run both of them, the post task runs usually in a wrong place. The expected/actual task orders are:

Command	Expected	Actual
invoke a b	pre a b post	pre a post b
invoke a b post	pre a b post	pre a post b
invoke pre a b post	pre a b post	pre a post b
invoke post a b post	post pre a b post	as expected 👍

With Invoke version: 0.11.1.

tasks.py

from invoke import task

@task
def pre(): print('pre')

@task
def post(): print('post')

@task(pre=[pre], post=[post])
def a(): print('a')

@task(pre=[pre], post=[post])
def b(): print('b')

Debug output

executor: Deduplicating tasks...
executor: <Task 'pre'>: ok
executor: <Call 'a', args: () kwargs: {}>: ok
executor: <Task 'post'>: ok <--------------------- ???
executor: <Task 'pre'>: skipping
executor: <Call 'b', args: () kwargs: {}>: ok
executor: <Task 'post'>: skipping <--------------- !!!
executor: Executing <Task 'pre'>
executor: Executing <Task 'a'> as a
executor: Executing <Task 'post'>
executor: Executing <Task 'b'> as b

[bitprophet]

Sounds strongly related to #45 - going to close this as a "dupe" but continue the conversation over there. Thanks for the detailed input!