Introduce on_runtime_upgrade

[shawntabrizi]

This is a basic implementation of the on_runtime_upgrade which triggers at the very beginning of block initialization, before system::initialize or module::on_initialize.

Introduces OnRuntimeUpgrade trait which exposes on_runtime_upgrade function which is triggered in the executor.

There is now an on_runtime_upgrade() function which can be defined in the decl_module macro.

We have also introduced a new storage item in FRAME System, RuntimeUpgraded which is a bool that expresses if a runtime upgrade occurred last block.

In the executive module, we read this storage item and execute the on_runtime_upgrade logic if needed.

Balances and Staking pallets have a new storage value StorageVersion which keeps track of a Releases enum, which will express the semantic version of the runtime storage, and should match 1:1 with the crate version.

Closes #4056

I have also removed traces of on_finalise and on_initialise as they have been deprecated since v1.0.

[drewstone]

Is this still planned?

[shawntabrizi]

@drewstone Would like to, just need to prioritize 2.0 and avoid extra noise.

[gui1117]

I very like the idea about having something to execute prior to on_initialize to avoid having conflict with other module.

I think saying that module must not call others in this function is a good contrain so all modules can update themself with no issue and not care about its public API.

(Maybe modules could opt-in for some on_runtime_upgrade API which is callable by other module during the on_runtime_upgrade function, by exposing a pub mod on_runtime_upgrade_module_api {..})

This doesn't solve any runtime upgrade logic that a runtime will need, it is intended to be used only for storage upgrade self contained inside a module IMHO.

In case a runtime wants to switch a module to another one or do big upgrade not self-contained, I think the logic should be written in node/runtime/src/lib.rs with an additional function. This function could call modules specific migration function for example:

fn runtime_upgrade() {
Balance::upgrade_from_other_currency_module(OldBalance);
// or
Balance::upgrade_path_for_kusama_1000();
}

And pallet_balance could expose this function under some cargo features,

[shawntabrizi]

Should be ready to review with the feedback given

[gui1117]

Looks good to me

[shawntabrizi]

@gnunicorn gucci gang