[BUG] casting PyObject * is broken in pure python mode

[matusvalo]

Describe the bug
For some cases casting PyObject * is failing during compilation with error: Cannot convert 'PyObject *' to Python object

To Reproduce
Following code is compiling with no error:

from cpython.ref cimport PyObject


foo = {"abc": 123}

cdef PyObject *bar = <PyObject *> foo

But in pure python version is failing:

import cython
from cython.cimports.cpython.ref import PyObject

foo = {"abc": 123}

bar: cython.pointer(PyObject) = cython.cast(cython.pointer(PyObject), foo)

Expected behavior

Pure python mode should reflect cython language.

Environment (please complete the following information):

• OS: Linux
• Python version: 3.9.2
• Cython version: master branch

[scoder]

This is intended. There is already a ticket where this was discussed. It only applies to module globals, which are Python objects unless explicitly declare()-d as something else. If you try the same thing inside of a function, it will probably work. I think it's ok to use a function in the documentation.

[matusvalo]

Hmm, yes it seems working. I did mistake when I was generelizing bug but it seems that following code snippet fails:

import cython
from cython.cimports.cpython.ref import PyObject

@cython.cfunc
def foo(obj: cython.pointer(PyObject)):
    pass

def main():
    python_dict = {"abc": 123}
    foo(cython.cast(cython.pointer(PyObject), python_dict))

compiling fails with following error:

$ cython -3a test.py

Error compiling Cython file:
------------------------------------------------------------
...
def foo(obj: cython.pointer(PyObject)):
    pass

def main():
    python_dict = {"abc": 123}
    foo(cython.cast(cython.pointer(PyObject), python_dict))
             ^
------------------------------------------------------------

test.py:12:14: Cannot convert 'PyObject *' to Python object

[matusvalo]

@scoder can you confirm the case? If yes I will close this issue and create new one with new snippet.

[da-woods]

The module globals issue is: #3944 (the issue that the the annotations on globals are ignored).

Your function-based version looks like a genuine bug (I think). I don't think it's necessary to create a new issue for it though

[matusvalo]

Ok closing this bug. Thank you @da-woods !