René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"changes to PyObject casting macros causing build failures with python-greenlet","articleBody":"\u003c!--\r\n  If you're new to Python and you're not sure whether what you're experiencing is a bug, the CPython issue tracker is not\r\n  the right place to seek help. Consider the following options instead:\r\n\r\n  - reading the Python tutorial: https://docs.python.org/3/tutorial/\r\n  - posting in the \"Users\" category on discuss.python.org: https://discuss.python.org/c/users/7\r\n  - emailing the Python-list mailing list: https://mail.python.org/mailman/listinfo/python-list\r\n  - searching our issue tracker (https://github.com/python/cpython/issues) to see if\r\n    your problem has already been reported\r\n--\u003e\r\n\r\n**Bug report**\r\n\r\nThere have been changes to how the macros for casting PyObject pointers per https://github.com/python/cpython/pull/91959#issuecomment-1114651243  by @vstinner any new compiler warnings are a regression.  \r\n\r\nThere were two types of errors in greenlet, one related to const correctness which has been fixed via https://github.com/python/cpython/pull/92138) and one related to casting wrapper classes (that has not been fixed).\r\n\r\nPer @serge-sans-paille in https://github.com/python/cpython/pull/92138#issuecomment-1116983125\r\n\r\n\u003e That's an interesting situation: greenlets are written in C++, and the object that raises issues is of type greenlet::refs::OwnedErrPiece that has a conversion operator to PyObject* (namely: https://github.com/python-greenlet/greenlet/blob/be41e1a24925326b72a02ef5cb6d1ed9643eb062/src/greenlet/greenlet_refs.hpp#L924 ) Using C-style cast or static_cast directly uses that operator so that's fine. But a reinterpret_cast won't work.\r\n\r\nand suggests a patch to CPython.\r\n\r\nhttps://github.com/python-greenlet/greenlet/pull/302 is a fix on the greenlet side.\r\n\r\nThe key line of the error is\r\n\r\n```\r\nsrc/greenlet/greenlet_refs.hpp: In member function ‘void greenlet::refs::PyErrPieces::normalize()’:\r\n/home/tcaswell/.pybuild/bleeding/include/python3.12/pyport.h:30:25: error: invalid cast from type ‘greenlet::refs::OwnedErrPiece’ to type ‘const PyObject*’ {aka ‘const _object*’}\r\n   30 |        const_cast\u003ctype\u003e(reinterpret_cast\u003cconst type\u003e(expr))\r\n      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\r\n```\r\n\r\nThis is also affecting https://github.com/python/pyperformance/issues/198\r\n\r\nA bunch of links: https://github.com/python/cpython/issues/92800#issuecomment-1126809930\r\n\r\n\r\n**Your environment**\r\n\r\n\u003c!-- Include as many relevant details as possible about the environment you experienced the bug in --\u003e\r\n\r\n- CPython versions tested on: main branch\r\n- Operating system and architecture: linux and x86_64 \r\n","author":{"url":"https://github.com/tacaswell","@type":"Person","name":"tacaswell"},"datePublished":"2022-05-17T20:33:11.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/92898/cpython/issues/92898"}