python-gmpy2 fails to build with Python 3.10.0a2.

src/gmpy2_convert_gmp.c:225:21: error: lvalue required as left operand of assignment
  225 |     Py_SIZE(result) = size;
      |                     ^
src/gmpy2_convert_gmp.c:228:25: error: lvalue required as left operand of assignment
  228 |         Py_SIZE(result) = - Py_SIZE(result);
      |    

https://docs.python.org/3.10/whatsnew/changelog.html#id11

bpo-39573: Convert Py_REFCNT() and Py_SIZE() macros to static inline functions. They cannot be used as l-value anymore: use Py_SET_REFCNT() and Py_SET_SIZE() to set an object reference count and size. This change is backward incompatible on purpose, to prepare the C API for an opaque PyObject structure.
https://bugs.python.org/issue39573

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.10/fedora-rawhide-x86_64/01757500-python-gmpy2/

For all our attempts to build python-gmpy2 with Python 3.10, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.10/package/python-gmpy2/

Testing and mass rebuild of packages is happening in copr. You can follow these instructions to test locally in mock if your package builds with Python 3.10:
https://copr.fedorainfracloud.org/coprs/g/python/python3.10/

Let us know here if you have any questions.

Python 3.10 will be included in Fedora 35. To make that update smoother, we're building Fedora packages with early pre-releases of Python 3.10.
A build failure prevents us from testing all dependent packages (transitive [Build]Requires), so if this package is required a lot, it's important for us to get it fixed soon.
We'd appreciate help from the people who know this package best, but if you don't want to work on this now, let us know so we can try to work around it on our side.