This should be very similar to what was done in the for statement (#15058).

Notes:

One difference between the for statement and comprehension is that the type of value expression needs to be inferred from different scope for the first comprehension. This could be done by extending the UnpackValue enum to include a Comprehension variant with a is_first boolean field.

I'm worried that this logic (

) would need to be duplicated (1) in infer_comprehension_definition when the target is just a name expression and (2) in Unpacker::unpack to get the unpack value type from the correct scope.