Conditional migrate call with extra MigrateInfo argument after contract update

[kulikthebird]

The result of this task is an implementation of the conditional migrate entry point calling after a contract's code update on the blockchain. Currently migrate is called every time the contract's binary is updated on the chain.

Procedure

The following procedure should be implemented:

1. Get the version of the on-chain state for the given contract by checking the Wasm binary before the code upgrade.
2. Get the state version supported by the new contract's binary (from the Wasm binary code).
3. Call migrate entry point if:

• at least one of the two versions is not provided, or
• both versions are provided and are different.

Migrate method

The migrate method needs to have a new parameter provided: info: MigrateInfo. In order to keep the backward compatibility, the VM should check the arity of the method implemented by the contract. If the arity is greater than 3, the following migrate signature should be assumed:

pub fn migrate(deps: DepsMut, env: Env, info: MigrateInfo, msg: MigrateMsg) -> StdResult<Response>;