Here's an issue for tracking the current state of mypy on CPython 3.10

CPython version: 3.10.0
mypy version: latest master (e6b91bd)

Dependencies:

• typed_ast is currently broken. Fixed on master, but no release to pypi yet (Allow compilation on python 3.10.0a6 typed_ast#155)
• typed_ast again broken in 3.10.0a7. PR Fix compilation on python 3.10.0a7 typed_ast#158
• lxml is currently broken due to a cython bug. The bug has been fixed in cython 0.29.22, but lxml hasn't been built with the new version yet (https://bugs.launchpad.net/lxml/+bug/1904900)
• virtualenv uses distutils, which is deprecated and will be removed in python 3.12. Mypy test-depends on virtualenv<20, and it looks like only virtualenv >=20 is still in active development. (Virtualenv pinned to <20 #10407)
• pytest breaks on python 3.10. This is already fixed upstream, but mypy pins pytest to <6.2, because of python 3.5 support

Tests:

• Some tests from FineGrainedSuite, FineGrainedCacheSuite and PythonCmdlineSuite` are broken, because cpython parser error messages changed. (Fix a bunch of tests broken by python 3.10 #10404)
  • Some occurrences of error: invalid syntax are now error: expected ':'
  • Some occurrences of error: unexpected EOF while parsing are now error: '(' was never closed
• Tests from SamplesSuite break with mypy/typeshed/stdlib/types.pyi:334: error: Name '_NotImplementedType' is not defined (Small fixes for Python 3.10 typeshed#5044)
• Enable CI for python 3.10 (Enable CI to use Python 3.10 #11294)

Features

• Pattern matching
  • Pattern matching is not yet supported (Support for python 3.10 match statement #10191)
  • Exhaustiveness checking for pattern matching (Reachability/exhaustiveness checking for match statements #12010)
  • Pattern matching in mypyc (Compiling code with match statements fails with an exception mypyc/mypyc#911)
• Support explicit TypeAlias (Support PEP 613 #9404)
• Support PEP 604 syntax for runtime use cases (Support PEP 604 syntax for runtime use cases #9880)
  • PEP 604 for TypeVar bounds new union syntax (types.Union) doesn't work on generic bounds #10949
• Support for dataclasses' kw_only ([dataclasses plugin] Support kw_only=True #10867)
• Support PEP 612 Parameter Specification Variables (PEP 612 tracking issue #8645)

Breaking changes

• mypyc is broken, because _PyObject_HasAttrId has been removed from CPython (bpo-41991: Remove _PyObject_HasAttrId cpython#22629). PR Fix mypyc failing to compile on CPython 3.10.0a6 #10202.
• mypy/sitepkgs.py imports distutils, which is deprecated and will be removed in python 3.12 (Only import distutils if it is needed #10203).

Misc

• Build Python 3.10 wheels
• Add Python 3.10 classifier