Add Never type to avoid ibc_packet_receive errors

[webmaster128]

When refactoring some ibc_packet_receive code in Nois I realized I really want type safety to ensure I don't shoot myself in the foot. A Never type makes explicit what is documented as best practive already: let ibc_packet_receive never return an error.

This way we keep compatibility with the current API (ibc_packet_receive returns Result<IbcReceiveResponse<C>, E> with E: ToString) but make it impossible to refactor code in a way that it returns an error (which is easy to get wrong with the ? operator).

[ethanfrey]

Looks good, happy for this type.

However, we no longer need this in receive as we auto-wrap errors in ibc receive as long as you use the same JSON format for errors as in ics20 and ics27.

We really should have this for ack and timeout, so the type is useful.

[ethanfrey]

Maybe add a comment that this is needed to satisfy the requirement of error type in cosmwasm results

[webmaster128]

However, we no longer need this in receive as we auto-wrap errors in ibc receive as long as you use the same JSON format for errors as in ics20 and ics27.

Where/how is this happening? Did I miss something that I should be aware of?

[ethanfrey]

We changed this when upgrading to ibc-go v3. This handles errors just in reply.

It was added in January. I know I had various discussions on GitHub here and I thought it was documented.

[webmaster128]

Oh, this PR might be obsolete then. I will check that.

[ethanfrey]

Never in other areas would be useful.
It was just the receive block we converted to app-level error instead of transaction rollback.

(And anyone that doesn't want that error format must ensure Never and manually handle)

[webmaster128]

Never in other areas would be useful.

Yeah, it seems like we have the same issue in ibc_packet_ack, right? You don't want to fail the ack transaction from the relayer just because of some failing ? in the CosmWasm implementation.