Follow PEP-484 and warn about "func(x: list = None)" without an explicit "typing.Optional[]" declaration.

See https://github.com/cython/cython/issues/3883

Avoid an unnecessary inefficiency in a regex, although it is not relevant in practice since the regex is only applied to Cython's only C code.
Found by GitHub CodeQL.

Rewrite the section that describes the differences between __cinit__() and __init__(), to make it clearer when to use which.

Partially reverts https://github.com/cython/cython/commit/1027db04fb7c5bbfea2b9bcdfce0b1f384e26a93

Make the extension types tutorial actually understandable by itself, without referring to obscure "previous code" and "our integration example" that come out of nowhere.

Allow globally forcing C file regeneration by setting the env var CYTHON_FORCE_REGEN=1, e.g. from external build systems.

Always regenerate .c/cpp output files when changing the Cython version. This is probably what users expect since silently keeping outdated files is error prone.

By disabling "CYTHON_FAST_THREAD_STATE" and "CYTHON_USE_EXC_INFO_STACK"

I think this still leaves some breakage in Coroutines.c but it's enough of a fix that Cython succeeds in building itself. Therefore I think it's worth doing now even if it doesn't fix everything.

Related to https://github.com/cython/cython/issues/4500

Add Cython.Utils to the list of compiled modules and include a faster @contextmanager for try-finally cases.

This reverts commit aaba1229.

Revert "Check for "Optional[ctype]" earlier because we need to make sure that "Optional[int]" etc. interprets "int" as (valid) Python int type and not (invalid) C int type."

This reverts commit f73108cc.

This reverts commit cd5fb480.

This reverts commit 7914e3b3.

Check for "Optional[ctype]" earlier because we need to make sure that "Optional[int]" etc. interprets "int" as (valid) Python int type and not (invalid) C int type.

See https://github.com/cython/cython/issues/3883

Improve the error message for "Optional[ctype]". Previously, it failed complaining about "or None", which wasn't the actual syntax construct on user side.

See https://github.com/cython/cython/issues/3883

See https://github.com/cython/cython/issues/3883

New decorator/function "@cython.dataclasses.dataclass" and "cython.dataclasses.field()" to mark dataclasses and their fields.

Tries to match the interface provided by a regular dataclass as much as possible.
This means taking the types from the dataclasses module if available (so they match exactly) or a fallback Python version that just implements the core parts (executed with "PyRun_String()" in the C source).

Use of placeholders in generated "__init__" code means the code in the C file isn't hugely readable. Probably not a huge issue, but don't really see a way round that.

As part of this I've also also implemented a Cython version of "typing.ClassVar". Although really designed for use with dataclasses it behaves sensibly when used in types in a normal cdef class. This is worth documenting more thoroughly.

Closes https://github.com/cython/cython/issues/2903

Fix division-by-zero crash in tests when the C ompiler discards the computational body of a Cython coroutine.

Add a new command line option so that
$ cythonize -M foo.pyx
produces a file `foo.c.dep` with the dependencies of foo.pyx, in addition to `foo.c`.
Try to write relative paths as much as possible.

Backport of https://github.com/cython/cython/pull/4563