GroupResult.as_tuple forget serialize group parent

[tbazadaykin]

celery -A ct report

software -> celery:4.0.2 (latentcall) kombu:4.0.2 py:2.7.9
            billiard:3.5.0.2 py-amqp:2.1.4
platform -> system:Linux arch:64bit, ELF imp:CPython
loader   -> celery.loaders.app.AppLoader
settings -> transport:amqp results:cache+memcached://127.0.0.1:11211/

broker_url: u'amqp://guest:********@localhost:5672//'
result_backend: u'cache+memcached://127.0.0.1:11211/'

Steps to reproduce

# ct.py

# ct.py
from __future__ import absolute_import, unicode_literals
from celery import Celery

app = Celery(
    'ct',
    broker='amqp://guest@localhost//',
    backend='cache+memcached://127.0.0.1:11211/'
)

@app.task
def nothing(*args):
   return args

if __name__ == '__main__':
    app.start()

Start worker

python ct.py worker -l INFO

In python console

>>> from celery import chain, group
>>> from celery.result import result_from_tuple
>>> from ct import nothing
>>> c = nothing.s() | group(nothing.s(), nothing.s())
>>> r = c.delay()
>>> r
<GroupResult: f46d7bcc-3140-40e8-9e21-d2f74eef6f28 [4854af6e-8e4a-48d8-98e9-d5f0eefcce20, 5c8d4ec1-84ff-4845-a9b2-9f07fd9bed19]>
>>> r.parent
<AsyncResult: a359ae60-ed18-4876-a67b-fc8cd83759a2>
>>> t = r.as_tuple()
>>> r2 = result_from_tuple(t)
>>> r2
<GroupResult: f46d7bcc-3140-40e8-9e21-d2f74eef6f28 [4854af6e-8e4a-48d8-98e9-d5f0eefcce20, 5c8d4ec1-84ff-4845-a9b2-9f07fd9bed19]>
>>> r2.parent

>>> r2.parent is None
True

Expected behavior

>>> r2 = result_from_tuple(t)
>>> r2.parent
<AsyncResult: a359ae60-ed18-4876-a67b-fc8cd83759a2>
>>>

[auvipy]

does this produce same against master branch

[tbazadaykin]

does this produce same against master branch

yes, it is

[pachewise]

wondering if GroupResult should have a parent? (seems like it should)...
writing a PR for this one.