asyncio.gather no DeprecationWarning if task are passed

[Dreamsorcerer]

BPO	44815
Nosy	@asvetlov, @ambv, @1st1, @yan12125, @Dreamsorcerer
PRs	bpo-44815: Always show deprecation in asyncio.gather/sleep() #27568 [3.9] bpo-44815: Always show deprecation in asyncio.gather/sleep() #27569

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-08-18.18:58:54.184>
created_at = <Date 2021-08-02.18:29:57.219>
labels = ['3.8', '3.9', 'expert-asyncio']
title = 'asyncio.gather no DeprecationWarning if task are passed'
updated_at = <Date 2021-09-04.02:42:34.542>
user = 'https://github.com/Dreamsorcerer'

bugs.python.org fields:

activity = <Date 2021-09-04.02:42:34.542>
actor = 'yan12125'
assignee = 'none'
closed = True
closed_date = <Date 2021-08-18.18:58:54.184>
closer = 'lukasz.langa'
components = ['asyncio']
creation = <Date 2021-08-02.18:29:57.219>
creator = 'dreamsorcerer'
dependencies = []
files = []
hgrepos = []
issue_num = 44815
keywords = ['patch']
message_count = 5.0
messages = ['398794', '398797', '399862', '399864', '401033']
nosy_count = 5.0
nosy_names = ['asvetlov', 'lukasz.langa', 'yselivanov', 'yan12125', 'dreamsorcerer']
pr_nums = ['27568', '27569']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue44815'
versions = ['Python 3.8', 'Python 3.9']

[Dreamsorcerer]

When calling asyncio.gather() a DeprecationWarning is only emitted if no tasks are passed (which is probably the exceptional case, rather than the standard one).

This has resulted in us missing this deprecated argument in aiohttp until we received a bug report from a user trying it out against the 3.10 beta.

For some reason the warning only appears under a `if not coros_or_futures:` block. I think it should be run regardless:
https://github.com/python/cpython/blob/3.9/Lib/asyncio/tasks.py#L757

[Dreamsorcerer]

There is another issue with asyncio.sleep() too, if the passed argument is 0. This also tripped up the tests in aiohttp (though I've also used an explicit 0 in production code to yield back to the loop).

[ambv]

New changeset b2779b2 by Sam Bull in branch '3.9':
[3.9] bpo-44815: Always show deprecation in asyncio.gather/sleep() (GH-27569)
b2779b2

[ambv]

Thanks, Sam! ✨ 🍰 ✨

[yan12125]

A regression in 3.9.7 (bpo-45097) seems related to this issue. Could you have a look?