regen() duplicates any non-list and non-tuple sequence

[Suor]

Checklist

• I have verified that the issue exists against the master branch of Celery.
• This has already been asked to the discussion group first.
• I have read the relevant section in the
  contribution guide
  on reporting bugs.
• I have checked the issues list
  for similar or identical bug reports.
• I have checked the pull requests list
  for existing proposed fixes.
• I have checked the commit log
  to find out if the bug was already fixed in the master branch.
• I have included all related issues and possible duplicate issues
  in this issue (If there are none, check this box anyway).

Mandatory Debugging Information

• I have included the output of celery -A proj report in the issue.
  (if you are not able to do this, then at least specify the Celery
  version affected).
• I have verified that the issue exists against the master branch of Celery.
• I have included the contents of pip freeze in the issue.
• I have included all the versions of all the external dependencies required
  to reproduce this bug.

Optional Debugging Information

• I have tried reproducing the issue on more than one Python version
  and/or implementation.
• I have tried reproducing the issue on more than one message broker and/or
  result backend.
• I have tried reproducing the issue on more than one version of the message
  broker and/or result backend.
• I have tried reproducing the issue on more than one operating system.
• I have tried reproducing the issue on more than one workers pool.
• I have tried reproducing the issue with autoscaling, retries,
  ETA/Countdown & rate limits disabled.
• I have tried reproducing the issue after downgrading
  and/or upgrading Celery and its dependencies.

Related Issues and Possible Duplicates

Related Issues

• None

Possible Duplicates

• None

Environment & Settings

Celery version:
5.1.0 (sun-harmonics)

celery report Output:

Steps to Reproduce

In [1]: from celery.utils.functional import regen
In [2]: from collections import deque
In [3]: l = regen(deque([1]))
In [4]: l
Out[4]: [1]
In [5]: l
Out[5]: [1, 1]
In [6]: l
Out[6]: [1, 1, 1]

When using .map() with non-list, non-tuple sequence passed all the items are processed 3 times:

@shared_task
def print_task(i):
    print(i)

# Print out 42 three times, can also use Django Queryset or any other Sequence
print_task.map(deque([42])).delay()

Required Dependencies

No dependencies

• Minimal Python Version: checked 3.8.2 and 3.9.0+
• Minimal Celery Version: checked 4.4.2, 4.4.7 and 5.10
• Minimal Kombu Version: N/A or Unknown
• Minimal Broker Version: N/A or Unknown
• Minimal Result Backend Version: N/A or Unknown
• Minimal OS and/or Kernel Version: N/A or Unknown
• Minimal Broker Client Version: N/A or Unknown
• Minimal Result Backend Client Version: N/A or Unknown

Python Packages

pip freeze Output:

amqp==5.0.6
backcall==0.2.0
billiard==3.6.4.0
-e git+git@github.com:celery/celery.git@025bad6e93087414b3ddc288060c367d1937774b#egg=celery
click==7.1.2
click-didyoumean==0.0.3
click-plugins==1.1.1
click-repl==0.1.6
decorator==5.0.9
ipython==7.23.1
ipython-genutils==0.2.0
jedi==0.18.0
kombu==5.1.0
matplotlib-inline==0.1.2
parso==0.8.2
pexpect==4.8.0
pickleshare==0.7.5
prompt-toolkit==3.0.18
ptyprocess==0.7.0
Pygments==2.9.0
pytz==2021.1
six==1.16.0
traitlets==5.0.5
vine==5.0.0
wcwidth==0.2.5

Other Dependencies

N/A

Minimally Reproducible Test Case

In [1]: from celery.utils.functional import regen
In [2]: from collections import deque
In [3]: l = regen(deque([1]))
In [4]: l
Out[4]: [1]
In [5]: l
Out[5]: [1, 1]
In [6]: l
Out[6]: [1, 1, 1]

Expected Behavior

Expected for regen() to not duplicate entires and for .map() to run each item once.

Actual Behavior

See above.

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[maybe-sybr]

Quick bisect suggest this has been broken since 998277302 when regen was first rewritten to make it lazy. We duplicate the elements because we don't set self.__done = True when we concretise the regen() instance when .data is accessed for something like an equaility check or repr() in the ipython example above.

I've got a bit of random time so I'll put up a PR for this shortly