system on_runtime_upgrade should be triggered after custom on runtime upgrade, similarly to other pallet

[gui1117]

About this code:

substrate/frame/executive/src/lib.rs

Lines 207 to 216 in acd1741

	pub fn execute_on_runtime_upgrade() -> frame_support::weights::Weight {
	let mut weight = 0;
	weight = weight.saturating_add(
	<frame_system::Pallet<System> as OnRuntimeUpgrade>::on_runtime_upgrade(),
	);
	weight = weight.saturating_add(COnRuntimeUpgrade::on_runtime_upgrade());
	weight = weight.saturating_add(<AllPallets as OnRuntimeUpgrade>::on_runtime_upgrade());
	weight
	}

I don't see why frame system pallet would take prioritised before the custom one whereas other pallet doesn't.

The custom on runtime upgrade should be able to do any kind of migration prior to pallet migration, allowing to bypass them.

cc @drewstone @al3mart

[al3mart]

I'm cc'ing @apopiak here :)

[drewstone]

@bkchr proposed removing all on_runtime_upgrade logic from the pallets and handling it directly at the runtime level, which seems like a good option imo. That way a team can check the references and order however they please.

[shawntabrizi]

Was there some bigger issue that was found which pointed to this?

[drewstone]

@shawntabrizi we're trying to run the next Edgeware upgrade and it seems the ref count migrations can't be updated on the fly (it migrates to triple count from double when we're still on single).

If there's no way to custom execute code before this, our only resolution is to fork substrate which I'd ideally try to avoid.