Incompatible with Cython 3.0a3

[jamadden]

Building with Cython 3.0a3 started producing these errors and warnings; Cython 3.0a1 was fine:

[1/1] Cythonizing src/gevent/libev/corecext.pyx
warning: src/gevent/libev/corecext.pyx:1288:0: Global name __SYSERR_CALLBACK matched from within class scope in contradiction to to Python 'class private name' rules. This may change in a future release.
warning: src/gevent/libev/corecext.pyx:1288:0: Global name __SYSERR_CALLBACK matched from within class scope in contradiction to to Python 'class private name' rules. This may change in a future release.
warning: src/gevent/libev/corecext.pyx:1288:0: Global name __SYSERR_CALLBACK matched from within class scope in contradiction to to Python 'class private name' rules. This may change in a future release.
warning: src/gevent/libev/corecext.pyx:1288:0: Global name __SYSERR_CALLBACK matched from within class scope in contradiction to to Python 'class private name' rules. This may change in a future release.

Error compiling Cython file:
------------------------------------------------------------
...
        if events & ~(libev.EV__IOFDSET | libev.EV_READ | libev.EV_WRITE):
            raise ValueError('illegal event mask: %r' % events)
        # All the vfd_functions are no-ops on POSIX
        cdef int vfd = libev.vfd_open(fd)
        libev.ev_io_init(&self._watcher, <void *>gevent_callback_io, vfd, events)
        self.__watcher = <libev.ev_watcher*>&self._watcher
                        ^
------------------------------------------------------------

src/gevent/libev/corecext.pyx:1027:25: Cannot convert 'ev_watcher *' to Python object

Error compiling Cython file:
------------------------------------------------------------
...
            raise ValueError('illegal event mask: %r' % events)
        # All the vfd_functions are no-ops on POSIX
        cdef int vfd = libev.vfd_open(fd)
        libev.ev_io_init(&self._watcher, <void *>gevent_callback_io, vfd, events)
        self.__watcher = <libev.ev_watcher*>&self._watcher
        self.__ss = &io_ss
                   ^
------------------------------------------------------------

src/gevent/libev/corecext.pyx:1028:20: Cannot convert 'start_and_stop *' to Python object

For now, I will pin to Cython<3.

[jamadden]

The problems begin in 3.0a2 and continue through 3.0a4.

[jamadden]

Re-opening pending cython/cython#3578

[scoder]

The errors that you got above are due to Cython now (mostly) following Python semantics on dunder names: cython/cython#3544

Specifically, as in Python, __somename now gives you a private, name-mangled attribute in classes. The obvious solution is to prefix the names only with a single underscore if they are not meant to be private to the class.

[jamadden]

The errors that you got above are due to Cython now (mostly) following Python semantics on dunder names

Thank you. I did eventually manage to figure that out, and it makes sense. The error message was initially a bit confusing since it's a step removed.