ICS28: Extend consumer InitGenesis

[mpoke]

Extends the CCV specification to cover the changes made by cosmos/interchain-security#30, i.e., InitGenesis on consumer should return a list of validator updates,
and cosmos/interchain-security#31, i.e., query the provider chain for a consumer chain genesis state.

Currently, the mechanism of disseminating the consumer chain genesis state is outside the scope of this specification. CCV assumes that the same genesis state is disseminated to all the correct validators in the initial validator set of the consumer chain. To aid developers, the mechanism implemented (see the above pull requests) is described as a possible approach.

[AdityaSripal]

Suggested change

	This is also where the application can inform the underlying consensus engine of the initial validator set.
	This is also where the application must inform the underlying consensus engine of the initial validator set.

The ABCI application overall MUST return a valset on init genesis. An individual module within the application may or may not return a valset, but something in application must return valset on initgenesis

[mpoke]

According to the ABCI documentation on InitChain,

If ResponseInitChain.Validators is empty, the initial validator set will be the RequestInitChain.Validators

However, in the SDK this line entails that "Exactly one module must return a non-empty validator set update to correctly initialize the chain"

@AdityaSripal How should we solve this conflict?

[AdityaSripal]

Ahh that is quite interesting. I don't know in practice if RequestInitChain does pass in a Validators field. This is a good question to clarify with the tendermint team

[mpoke]

From my discussion with @sergio-mena:

RequestInitChain contains the set of validators coming from the genesis file. When handling RequestInitChain , the app (e.g., SDK) can override that set with a different one. If the app does not return anything in ResponseInitChain , then Tendermint will simply reuse the value it used to populate RequestInitChain , which is the one found in the genesis info

If the genesis info contains an empty validator set, and the app doesn't provide anything in ResponseInitChain either, then Tendermint returns an error.

The restriction introduced in the SDK is further constraining this behavior: the SDK must always override the initial validator set . But an app using directly ABCI, doesn't necessarily need to override the validator set from genesis

@AdityaSripal I would suggest to keep the IBC spec consistent with the ABCI spec and not Cosmos SDK, i.e., leave "the application MAY inform". What do you say?
I also think this should be address in Cosmos SDK to avoid confusion and possible bugs.