AsyncEngine.begin() returns _trans_ctx instead of expected AsyncTransaction

[blazewicz]

AsyncConnection.begin() returns AsyncTransaction, like one would expect:

sqlalchemy2-stubs/sqlalchemy-stubs/ext/asyncio/engine.pyi

Line 50 in e6ae4cc

def begin(self) -> AsyncTransaction: ...

however, AsyncEngine.begin() returns _trans_ctx:

sqlalchemy2-stubs/sqlalchemy-stubs/ext/asyncio/engine.pyi

Line 116 in e6ae4cc

def begin(self) -> _trans_ctx: ...

This leads to following errors, when user declares argument type to AsyncTransaction.

error: Argument "bar" to "foo" has incompatible type "_trans_ctx"; expected "AsyncTransaction"

[CaselIT]

Hi,

The typing itself is actually correct, see https://github.com/sqlalchemy/sqlalchemy/blob/master/lib/sqlalchemy/ext/asyncio/engine.py

But I'm not entirely sure if we could make the two begin behave more similarly wrt returned object. @zzzeek can't we return an async transaction from the engine.begin?

[CaselIT]

I think this is a won't fix for now