Consensus versioning & migrations

[aaronc]

An idea that came up on telegram with regards to this debate over tagging v0.40.2 vs 0.41 was that we could have separate consensus versions.

How about starting by adding a ConsensusVersion() uint64 method to AppModule?

We could also add an MigrateFrom(ctx sdk.Context, version uint64) method to AppModule to do in place state migrations. We could even add support in x/upgrade to generate an upgrade handler which 1) reads the current consensus versions from state and 2) calls each module's MigrateFrom method to migrate state from the current to the latest version.

What do you think?

[amaury1093]

sgtm. It seems to me that the MigrateFrom method is way more flexible than the current StoreUpgrades, it can for sure add/rename/delete stores. If we add support for MigrateFrom in x/upgrade, then I don't see the point of having StoreUpgrades anymore. Is that correct?

[aaronc]

StoreUpgrades is totally unrelated. Sorry it's confusing. Let's chat about it later

[hxrts]

related: tendermint/spec#222