Add __callback__ property to weakref type

[Copilot]

RustPython's weakref type was missing the __callback__ read-only property, blocking PyO3 weakref compatibility (e.g. reference.getattr("__callback__") fails).

Changes

• crates/vm/src/object/core.rs: Add get_callback() to PyWeak — reads the callback field under the stripe lock using the same double-check pattern as upgrade()
• crates/vm/src/builtins/weakref.rs: Expose __callback__ as a read-only #[pygetset]
• Lib/test/test_weakref.py: Remove expectedFailure from test_callback_attribute and test_callback_attribute_after_deletion
• extra_tests/snippets/stdlib_weakref.py: Add regression coverage

>>> import weakref
>>> class C: pass
>>> o = C()
>>> weakref.ref(o).__callback__ is None
True
>>> cb = lambda r: None
>>> weakref.ref(o, cb).__callback__ is cb
True

Semantics match CPython: returns the callback if alive, None if no callback was set or referent was collected (callback consumed during clear).

[github-actions]

📦 Library Dependencies

The following Lib/ modules were modified. Here are their dependencies:

[x] lib: cpython/Lib/weakref.py
[x] lib: cpython/Lib/_weakrefset.py
[x] test: cpython/Lib/test/test_weakref.py (TODO: 13)
[ ] test: cpython/Lib/test/test_weakset.py

dependencies:

• weakref

dependent tests: (205 tests)

• weakref: test_array test_ast test_asyncio test_code test_concurrent_futures test_context test_contextlib test_copy test_ctypes test_deque test_descr test_dict test_enum test_exceptions test_file test_fileio test_frame test_functools test_gc test_generators test_genericalias test_importlib test_inspect test_io test_ipaddress test_itertools test_logging test_memoryio test_memoryview test_mmap test_ordered_dict test_pickle test_picklebuffer test_queue test_re test_scope test_set test_slice test_socket test_sqlite3 test_ssl test_struct test_sys test_tempfile test_thread test_threading test_threading_local test_type_params test_types test_typing test_unittest test_uuid test_weakref test_weakset test_xml_etree
  • asyncio: test_asyncio test_contextlib_async test_os test_sys_settrace test_unittest
  • bdb: test_bdb
  • concurrent.futures.process: test_compileall test_concurrent_futures
  • copy: test_bytes test_codecs test_collections test_copyreg test_coroutines test_csv test_decimal test_defaultdict test_dictviews test_email test_fractions test_http_cookies test_minidom test_opcache test_optparse test_platform test_plistlib test_posix test_site test_statistics test_sysconfig test_tomllib test_urllib2 test_xml_dom_minicompat test_zlib
    • argparse: test_argparse
    • collections: test_annotationlib test_bisect test_builtin test_c_locale_coercion test_call test_configparser test_contains test_ctypes test_exception_group test_fileinput test_funcattrs test_hash test_httpservers test_iter test_iterlen test_json test_math test_monitoring test_pathlib test_patma test_pprint test_pydoc test_random test_reprlib test_richcmp test_shelve test_sqlite3 test_string test_traceback test_tuple test_urllib test_userdict test_userlist test_userstring test_with
    • dataclasses: test__colorize test_ctypes test_regrtest test_zoneinfo
    • email.generator: test_email
    • gettext: test_gettext test_tools
    • http.cookiejar: test_http_cookiejar
    • http.server: test_robotparser test_urllib2_localnet test_xmlrpc
    • logging.handlers: test_pkgutil
    • mailbox: test_mailbox
    • smtplib: test_smtplib test_smtpnet
    • tarfile: test_shutil test_tarfile
    • webbrowser: test_webbrowser
  • inspect: test_abc test_asyncgen test_buffer test_grammar test_ntpath test_operator test_posixpath test_signal test_type_annotations test_yield_from test_zipimport
    • ast: test_compile test_compiler_codegen test_dis test_fstring test_future_stmt test_type_comments test_ucn test_unparse
    • cmd: test_cmd
    • importlib.metadata: test_importlib
    • pkgutil: test_runpy
    • rlcompleter: test_rlcompleter
    • trace: test_trace
  • logging: test_hashlib test_support test_urllib2net
    • hashlib: test_hmac test_unicodedata
    • multiprocessing.util: test_concurrent_futures
    • venv: test_venv
  • multiprocessing: test_fcntl test_multiprocessing_main_handling
  • symtable: test_symtable
  • tempfile: test_bz2 test_cmd_line test_ctypes test_doctest test_ensurepip test_faulthandler test_filecmp test_importlib test_launcher test_linecache test_modulefinder test_pkg test_py_compile test_selectors test_string_literals test_subprocess test_tabnanny test_termios test_threadedtempfile test_tokenize test_urllib_response test_winconsoleio test_zipapp test_zipfile test_zipfile64 test_zstd
    • ctypes.util: test_ctypes
    • urllib.request: test_sax test_urllibnet

Legend:

• [+] path exists in CPython
• [x] up-to-date, [ ] outdated

[youknowone]

@copilot Fix CI failure

[Copilot]

@copilot Fix CI failure

Fixed in 0d51428 — the lint failure was a ruff format issue with a long assert message in extra_tests/snippets/stdlib_weakref.py.