Unreachable yield should still make a function a generator

[kepler-5]

Describe the bug
According to https://docs.python.org/3/reference/expressions.html#yieldexpr, when a function contains a yield expression, it becomes a generator function, regardless of the reachability of that yield expression. But in the code below, an unconditional return makes the yield unreachable and pyright seems to stop type checking as soon as it sees the return.

def foo() -> None:
    return
    yield 42

This function signature is accepted by pyright but seems incorrect, since the presence of the yield keyword, even if unreachable, turns this function into a generator function. Calling foo() as written gives me <generator object foo at 0x12dfd54e0> rather than the promised None.

Removing the return, I get the expected error message:

Return type of generator function must be compatible with "Generator[Literal[42], Any, Any]"
  Type cannot be assigned to type "None"

I believe this to be a bug and I couldn't find a duplicate, but I'm definitely no expert so I'm sorry if I'm off about something here.

VS Code extension or command-line
Pylance v2023.9.10

[erictraut]

Pyright validates that the annotated return type of a generator function is compatible with Generator (or AsyncGenerator), but it currently does this only when type checkin a yield or yield to statement. In your example, the yield statement was determined to be unreachable, and errors detected when analyzing unreachable statements are suppressed.

I've enhanced the logic that validates the annotated return address for a generator so it is performed regardless of whether a yield or yield from statement is evaluated. This will be included in the next release.

[erictraut]

This is addressed in pyright 1.1.328, which I just published. It will also be included in a future release of pylance.