Detect redundant unions with buffer/bytes types?

[Akuli]

Currently this annotation doesn't cause a lint error: (taken from python/typeshed#10432 )

from _typeshed import ReadOnlyBuffer

def farm_msg(__farm_name: str, __message: str | bytes | ReadOnlyBuffer) -> None: ...

If I understand the buffer situation correctly, bytes | ReadOnlyBuffer is equivalent to ReadOnlyBuffer, because typeshed claims that bytes implements __buffer__ on all Python versions.

It feels like a good idea to detect unions where bytes types are used like this, similar to Literal[1] | int and other checks we already have. But it feels like a bad idea to make flake8-pyi aware of _typeshed.ReadOnlyBuffer etc and their subtyping rules. I'm not sure.

[AlexWaygood]

It feels like a good idea to detect unions where bytes types are used like this, similar to Literal[1] | int and other checks we already have. But it feels like a bad idea to make flake8-pyi aware of _typeshed.ReadOnlyBuffer etc and their subtyping rules. I'm not sure.

A general-purpose way of detecting redundant unions could only ever be implemented by a type checker, since they're much better equipped to resolve imports across modules than we'll ever be. We have a much simpler design that only analyses a module at a time, and I'd like to keep it that way (I'm not sure flake8's plugin system even would allow us to analyse multiple modules at a time). So we'll need to weigh up whether it's worth special-casing these specific types from _typeshed or not.

[Avasam]

Relevant pyright discussion: microsoft/pyright#3949

[AlexWaygood]

So we'll need to weigh up whether it's worth special-casing these specific types from _typeshed or not.

My feeling is that this probably doesn't come up enough for it to be worth adding this special-casing — WDYT?