Remove error string from ics27 ack

[colin-axner]

Summary of Bug

The ics27 host submodule currently returns the error string from message execution in the channel acknowledgement. If this value changes between patch releases, the marshalled acknowledgement will also changes. Nodes running different patch versions will set in state different acknowledgements and thus reach an app hash mismatch. Making error strings changes state machine breaking is too strict of a requirement for ics27 to impose on an entire chain.

Fix

Remove the error string from the channel acknowledgement. Emit the message execution error in the events.

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[damiannolan]

I've opened #751 with a fix for this. Should ICS27 be emitting more general events as well? Off the top of my head:

• successful ack
• account registration
• successful msg execution

I've also noticed this issue is true for transfer? Would you like me to do the same there?

[colin-axner]

I've also noticed this issue is true for transfer? Would you like me to do the same there?

This is a really good point. We have two options:

• ensure no calls to external modules outside ibc-go include error messages in our ack
• remove the error string

I think we should probably remove the error string and document this issue. I think we could handle ensuring external calls are not included in our ack, but I don't think we can expect other developers developing IBC app modules to be aware of this issue, and since they will copy our code, it is probably best to keep it simple