Compatibility matrix Core x SDK

[julienrbrt]

With changes like this we need to start to create a compatibility matrix of core x SDK. As for instance a module implementing PreBlock from core v0.11.0, in a v0.47 chain will have no effect.

Originally posted by @julienrbrt in #17468 (comment)

[julienrbrt]

@aaronc / @tac0turtle do you have a better idea than a simple table like: https://github.com/cosmos/cosmos-sdk/blob/main/proto/README.md ?

My main issue is that core will still be compatible, but not interfaces will be available/implemented in earlier SDK versions. Possibly, the most straightforward is to add a // Since: Cosmos SDK v0.x.x comment like we do in .proto in each go doc instead of creating a table. However, given that core is SDK agnostic, it may be weird as well.

[tac0turtle]

could you explain the issue with earlier versions?

If possible avoiding Since: ... would be better as this eludes to misuse of an api if we have to share that information in a comment.

[julienrbrt]

could you explain the issue with earlier versions?

If possible avoiding Since: ... would be better as this eludes to misuse of an api if we have to share that information in a comment.

As a module developer, I look at the Core API in pkg.go.dev, and I see, for instance, that a module can implement PreBlock. If I make my module available for v0.47 and v0.50 chains, it will not behave the same, as v0.47 chains will never run the PreBlock, while both chains have the same core version as dependency. If I just look at the Core API and docs, I have currently no way to know that. I need to know the internal of the SDK to be able to know that.

I am not a fan of Since: ... either, but a compatibility matrix may look quite confusing:

core version	sdk version	appmodule.HasPreBlocker	appmodule.HasEndBlocker	...
v0.11.0	v0.50	✅	✅
v0.11.0	v0.47	🟥	✅
v0.10.0	v0.47	N/A	✅

[alexanderbez]

Personally, i think we should have both -- a compatibility matrix and annotations in comments. As a dev, there are times where I just simply want to know the compatibility and not have to dig through specific APIs I'm trying to use.