Breaking change in PyDate_FromTimeStamp API

[pganssle]

BPO	36025
Nosy	@abalkin, @encukou, @ambv, @berkerpeksag, @serhiy-storchaka, @pganssle
PRs	bpo-36025: Restore original function API for PyDate_FromTimestamp #11922

^{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 = 'https://github.com/pganssle'
closed_at = <Date 2019-04-27.19:59:54.756>
created_at = <Date 2019-02-18.17:22:05.656>
labels = ['3.8', 'type-bug', 'library', 'release-blocker']
title = 'Breaking change in PyDate_FromTimeStamp API'
updated_at = <Date 2019-04-27.19:59:54.756>
user = 'https://github.com/pganssle'

bugs.python.org fields:

activity = <Date 2019-04-27.19:59:54.756>
actor = 'berker.peksag'
assignee = 'p-ganssle'
closed = True
closed_date = <Date 2019-04-27.19:59:54.756>
closer = 'berker.peksag'
components = ['Library (Lib)']
creation = <Date 2019-02-18.17:22:05.656>
creator = 'p-ganssle'
dependencies = []
files = []
hgrepos = []
issue_num = 36025
keywords = ['patch']
message_count = 4.0
messages = ['335854', '335858', '335893', '341009']
nosy_count = 6.0
nosy_names = ['belopolsky', 'petr.viktorin', 'lukasz.langa', 'berker.peksag', 'serhiy.storchaka', 'p-ganssle']
pr_nums = ['11922']
priority = 'release blocker'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue36025'
versions = ['Python 3.8']

[pganssle]

The PyO3 test suite has been breaking since the alpha release of Python 3.8 because PyDateTimeAPI->Date_FromTimeStamp has had a breaking change in its API: PyO3/pyo3#352

I believe this happened when datetime.date.fromtimestamp and datetime.datetime.fromtimestamp were converted over to using the argument clinic. The function date_from_local_object was renamed to date_fromtimestamp, without a corresponding change to the PyDateTimeCAPI struct.

[pganssle]

I've put *a* fix in there by introducing a new wrapper function. Ideally we would just point the C API at the argument clinic-generated function, but because it takes a single positional argument the argument clinic outputs a METH_O function instead of METH_VARARGS.

I think these are the options:

1. Modify the argument clinic spec to force METH_VARARGS for a single positional argument taking an object - if that's possible.
2. Maintain a wrapper function for the C API that just unpacks the tuple and passes it to the date_fromtimestamp function that the argument clinic is *also* wrapping.
3. Revert the argument clinic change and manually manage the date_fromtimestamp function as a METH_VARARGS classmethod.

I don't know enough about the argument clinic to know if #1 is feasible, if it is and someone can point me in the right direction, I can update my PR. If not, I think I mildly prefer #2, since maintaining a thin wrapper that unpacks a tuple is not terribly difficult compared to maintaining the method definition stuff.

Since this was an accidental break in the C API, I've marked it as a release blocker.

[serhiy-storchaka]

I prefer option 2. Your PR LGTM.

[berkerpeksag]

New changeset 4d8c8c0 by Berker Peksag (Paul Ganssle) in branch 'master':
bpo-36025: Fix PyDate_FromTimestamp API (GH-11922)
4d8c8c0