Add migration docs for 02-client refactor

[colin-axner]

Summary

The migration document should clearly explain how to go from the old 02-client API to the new API

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[catShaark]

can I try doing this ?

[crodriguezvega]

Sure, @catShaark. Thanks for volunteering!

Would it be possible for you to open a PR for this issue before the end of next week? As you can see in our project board this issue is part of our current iteration (ending April 29th) and the goal would be to complete these issues in the board to create an alpha tag.

@colin-axner would you like to add any more details in the issue of what you would like to see in the docs so that @catShaark can take that into account?

[colin-axner]

Excellent @catShaark, that'd be wonderful.

Here's what I had in mind:

There's a few major changes involved here:

• light clients now need to manage setting of client and consensus states for all interface functions (UpdateState, UpdateStateOnMisbehaviour, VerifyUpgradeAndUpdateState, CheckSubstituteAndUpdateState) Modify CheckHeaderAndUpdateState to set client state/consensus states in IBC light client implementations #284
• CheckHeaderAndUpdateState has been split into 4 functions, VerifyClientMessage, CheckForMisbehaviour, UpdateState, and UpdateStateOnMisbehaviour Split CheckHeaderAndUpdateState into 4 functions #668
• exported.Header/exported.Misbehaviour interface types have been merged and renamed to ClientMessage 02-client: merge misbehavior & header interfaces #1107

some minor changes:

• GetTimestampAtHeight has been added to the ClientState interface Add GetTimestampAtHeight to client state interface #876
• CheckMisbehaviourAndUpdateState has been removed (encapsulated in the usage of the 4 functions list above, VerifyClientMessage, CheckForMisbehaviour, etc) Remove CheckMisbehaviourAndUpdateState from the ClientState interface #1189
• GetRoot has been removed from ConsensusState interface Remove GetRoot from ConsensusState interface #670

Let me know if you have any questions. If you only feel comfortable adding entries for a few of these changes, that's totally fine, we will pick up the rest. Any contribution is greatly appreciated :)

[catShaark]

@colin-axner thanks for the summary, I will dig into this and ask you if I get stuck.

[catShaark]

@colin-axner should we add in that we remove "09-localhost" client implementation.

[catShaark]

so I want to add these entries :

• remove “09-localhost” client implementation
• client keeper CheckMisbehaviourAndUpdateState merge into UpdateClient
• MsgSubmitMisbehaviour is deprecated as MsgUpdateClient can handle header which include misbehaviour
• 07-tendermint client GetConsensusState has been modified

But I guess some of these (or all of these) might be irrelevant so I have to ask you

[colin-axner]

@colin-axner should we add in that we remove "09-localhost" client implementation.

yes please!

so I want to add these entries

The only one I wouldn't include is:

• 07-tendermint client GetConsensusState has been modified

[catShaark]

Yeah, I'll apply the changes accordingly and be more descriptive with the entries

[colin-axner]

thanks @catShaark! Closed by #1287