Also adds a check whether we have the GIL before doing so. This
is important because Py_UNBLOCK_THREADS is documented as unsafe
if we don't hold the GIL.

Closes https://github.com/cython/cython/issues/4137

Follows the implementation in CPython, which does a lookup in sys.modules if the attribute lookup on a package fails.

Closes https://github.com/cython/cython/issues/4390

Closes https://github.com/cython/cython/issues/3293

Very little works at present, there looks to be huge memory-leaks,
and the test-suite runs very slowly. It definitely isn't worth adding
anything on Github Actions at this stage.

It's just designed to get over the initial hurdle so that it
can be tested and improvements can be made if anyone is
inclined.

Add "tp_pypy_flags" field to PyTypeObject struct when compiling in PyPy 6.0+ in order to avoid C compiler warnings about an uninitialised struct field.

This reverts commit 751532a5.

This reverts commit f5aa00bb.

See https://github.com/cython/cython/issues/2529

Exclude a C++17 test (currently in PR #3294) on macOS since it suffers from the same incompatibility issues as the other C++17 tests.

Closes https://github.com/cython/cython/issues/3938

Closes https://github.com/cython/cython/issues/3938

With Cython syntax, we ignore the exception_check when a Python object is returned.
In pure Python mode, with a Python object type as return type, we reject it.
Instead of raising an error, we now just reset exception_check to False.

Found in https://github.com/cython/cython/issues/2529

Closes https://github.com/cython/cython/issues/2304

* Warn when cyfunction.__[kw]defaults__ is changed

Cython can't make use of these new defaults so it seems sensible
to alert the user (even if we're choosing to allow the assignment
for compatibility reasons).

I know the warning mechanism is somewhat heavy. I think this is
OK because it's unlikely that users will be repeatedly assigning
to these attributes in a time-critical loop.

Doesn't fix https://github.com/cython/cython/issues/2650, but hopefully alerts users to it.

CPython added PyMem_RawCalloc and PyMem_Calloc in version 3.5.

The #defines of PyMem_RawMalloc, PyMem_RawRealloc, and PyMem_RawFree
are removed from Cython/Utility/ModuleSetupCode.c since the Raw versions allow
use without the GIL but the non-Raw versions do not.
Co-authored-by: William Schwartz <wkschwartz@gmail.com>

Closes https://github.com/cython/cython/pull/3050
Closes https://github.com/cython/cython/pull/3047

Closes https://github.com/cython/cython/issues/2760

It requires Py_DecodeLocale which appears in 3.5. This is causing
it to fail on Windows. It's somehow passing on Linux for reasons
that I don't understand (but it really shouldn't be)

Specifically this disallows memoryviews, but it extends to any future type that Cython has to generate manual reference counting code for.

Closes https://github.com/cython/cython/issues/3085

Fixes https://github.com/cython/cython/issues/4354

As suggested in https://github.com/cython/cython/pull/4471#issuecomment-979489947
I don't think that we're getting any benefit from running the pypy
known bugs test as part of the CI (and it's causing minor problems).