Make completion signatures depend on the Receiver type

[maikel]

This draft PR tracks my attempt to make get_completion_signatures take the receiver type instead of the env. If that works out it would solve some pending issues wrt to detecting whether connecting child senders throws or not.

[copy-pr-bot]

This pull request requires additional validation before any workflows can run on NVIDIA's runners.

Pull request vetters can view their responsibilities here.

Contributors can view more details about this message here.

[ericniebler]

Have you considered doing away with get_completion_signatures and just having connect, with the completion signatures as a nested typedef on the operation state?

[maikel]

Have you considered doing away with get_completion_signatures and just having connect, with the completion signatures as a nested typedef on the operation state?

Hm Im not sure whether computing completion sigs can require a complete definition of the operation state. I think it must require a complete definition of the receiver, tho (for what i try to achieve)

[ericniebler]

I wonder if this experiment would be easier in the smaller, cleaner ustdex repo.

[ericniebler]

Have you considered doing away with get_completion_signatures and just having connect, with the completion signatures as a nested typedef on the operation state?

i have made this change in the ericniebler/ustdex and it works well. this is the direction i would like to pursue for stdexec.

[ericniebler]

the sender_in concept is no longer needed, right? sender_to is enough.