Fix up support for PyPy 3.10

[Nick Pope]

Python 3.10 support was released in PyPy v7.3.12 in June 2023.

It was highlighted ​here that a number of tests are failing, and here and here that the changes in #31262 have introduced some large "regressions". It turns out that there is a ​bug in PyPy related to abstract base classes being used for isinstance() checks with structural pattern matching. This can be resolved by either waiting for a fix in PyPy or implementing a workaround by removing the pattern matching approach. Aside from that, however, there are also a number of other failures and crashes that still need to be addressed.

​PyPy claims to be highly compatible with CPython and that it supports Django. Django ​claims to be compatible with PyPy. We need to determine whether it is possible to fix these issues or whether we need to remove this claim.

One of the issues is that currently there is no CI to ensure that PyPy support remains in a working state. An initial ​PR has been created to run a daily scheduled test run on SQLite only. Later it may make sense to enable triggering testing via assigning a label to a PR.

[Nick Pope]

​PR

[GitHub <noreply@…>]

In 0d407bc:

Refs #34986 -- Installed libmemcached-dev in PyPy 3.10 daily builds.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 174369a9:

Refs #34986 -- Avoided pickling error in DjangoUnicodeDecodeError.

By using the existing object reference instead of a custom one, pickling
related issues when running the test suite in parallel can be avoided.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 9baaf89:

Refs #34986 -- Added django.utils.version.PYPY.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 6089230:

Refs #34986 -- Fixed mocking in utils_tests.test_http.HttpDateProcessingTests.test_parsing_rfc850.

Mocking in the datetime module can be tricky. In CPython the datetime
C module is used, but PyPy uses a pure Python implementation. This
caused issues with the prior approach to mocking datetime.datetime.

See ​https://docs.python.org/3/library/unittest.mock-examples.html#partial-mocking

[Mariusz Felisiak <felisiak.mariusz@…>]

In 051dbb53:

Refs #34986 -- Added PyPy support to django.utils.autoreload.get_child_arguments().

It seems that sys._xoptions is also supported on PyPy.

[Mariusz Felisiak <felisiak.mariusz@…>]

In baf705f3:

Refs #34986 -- Fixed some test assertions for PyPy.

These failures were due to minor inconsistencies or implementation
differences between CPython and PyPy.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 5f9e5c1:

Refs #34822, Refs #34986 -- Fixed migrations serializer support for functools.lru_cache().

It turns out that functools._lru_cache_wrapper is only a class when
CPython's _functools C module provides it, otherwise it is a function.
PyPy also provides it as a function.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 06c5cb12:

Refs #34986 -- Removed redundant CustomChoicesTests.test_timezone_unsupported().

This test relied on the behavior of subclassing datetime.timezone
which is not permitted by the C-extension version of CPython's
datetime module. This restriction isn't enforced by the pure
Python version, nor by PyPy.

See ​https://github.com/python/cpython/issues/112451

It's not critical, and doesn't test any Django behavior, so just
remove it.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 1c3614e3:

Refs #34986 -- Avoided implementation-specific unpickleable types.

The implementation of some core types differ between CPython and PyPy
and this may affect the way that pickling works such that errors are
raised in differing locations in the interpreter or not at all.

Use our own custom non-pickleable type instead to avoid these quirks.

[Mariusz Felisiak <felisiak.mariusz@…>]

In fb921638:

Refs #34986 -- Moved garbage_collect() helper to django.test.utils.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 66d58e77:

Refs #34986 -- Added PyPy to tox.ini.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 958a590e:

Refs #34986 -- Used non-binary build of psycopg for PyPy.

[Mariusz Felisiak <felisiak.mariusz@…>]

In af6e7e3d:

Refs #34986 -- Fixed backends.postgresql.test_server_side_cursors.ServerSideCursorsPostgres tests for PyPy.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 2dca98f:

Refs #34986 -- Added PyPy 3.10 with PostgreSQL to daily builds.