mypy 2.0 big change list

[hauntsaninja]

This is a reminder list for changes we may want to do in a major version (that we know are relatively easy to flip on).

• Local partial types Allow inverting --local-partial-types #18377 Enable local partial types by default #10169
• PEP 688 change bytearray memoryview promotion by default Enable strict_bytes by default #18371
• Remove logic for legacy bundled stubs Remove logic for legacy bundled stubs #18372
• SQLite cache
• Delete the Python 2 extra from setup.py Delete Python 2 extra #18374

Needs more discussion:

• Get rid of --no-namespace-packages
• Interpret type as type[Any]?
• Move func-returns-value to disabled by default error code?

For general not-so-easy changes we want to do, see #16472 (major/minor isn't the most meaningful for a lot of the most important changes we want to do, e.g. --new-type-inference was in 1.7)

See also https://github.com/python/mypy/wiki/Release-Process#policy-for-backward-incompatible-changes

(feel free to edit)

[brianschubert]

• Enable --warn-unreachable in --strict in Mypy 2.0 #18078

[JukkaL]

I'd also like to add narrowing on initial assignment (#2008). We'd need to first add a feature flag to opt-in to the new behavior before 2.0.

[emmatyping]

I believe the behavior change in #6577 would likely be breaking, so mypy 2.0 would be a good time to do it.

[emmatyping]

I also think making --check-untyped-defs the default is a pretty significant change that we'd probably want to communicate and make in mypy 2.0 ref #6646