Store validator self-vote in bags-list, and allow them to be trimmed for election (#10821)

* Implement the new validator-in-bags-list scenario + migration

* Apply suggestions from code review

Co-authored-by: Zeke Mostov <z.mostov@gmail.com>

* some review comments

* guard the migration

* some review comments

* Fix tests 🤦‍♂️

* Fix build

* fix weight_of_fn

* reformat line width

* make const

* use weight of fn cached

* SortedListProvider -> VoterList

* Fix all build and docs

* check post migration

Co-authored-by: Zeke Mostov <z.mostov@gmail.com>

substrate/frame/staking/src/migrations.rs

@@ -17,13 +17,83 @@
 //! Storage migrations for the Staking pallet.
 
 use super::*;
+use frame_election_provider_support::SortedListProvider;
+use frame_support::traits::OnRuntimeUpgrade;
+
+pub mod v9 {
+	use super::*;
+
+	/// Migration implementation that injects all validators into sorted list.
+	///
+	/// This is only useful for chains that started their `VoterList` just based on nominators.
+	pub struct InjectValidatorsIntoVoterList<T>(sp_std::marker::PhantomData<T>);
+	impl<T: Config> OnRuntimeUpgrade for InjectValidatorsIntoVoterList<T> {
+		fn on_runtime_upgrade() -> Weight {
+			if StorageVersion::<T>::get() == Releases::V8_0_0 {
+				let prev_count = T::VoterList::count();
+				let weight_of_cached = Pallet::<T>::weight_of_fn();
+				for (v, _) in Validators::<T>::iter() {
+					let weight = weight_of_cached(&v);
+					let _ = T::VoterList::on_insert(v.clone(), weight).map_err(|err| {
+						log!(warn, "failed to insert {:?} into VoterList: {:?}", v, err)
+					});
+				}
+
+				log!(
+					info,
+					"injected a total of {} new voters, prev count: {} next count: {}, updating to version 9",
+					Validators::<T>::count(),
+					prev_count,
+					T::VoterList::count(),
+				);
+
+				StorageVersion::<T>::put(crate::Releases::V9_0_0);
+				T::BlockWeights::get().max_block
+			} else {
+				log!(
+					warn,
+					"InjectValidatorsIntoVoterList being executed on the wrong storage \
+				version, expected Releases::V8_0_0"
+				);
+				T::DbWeight::get().reads(1)
+			}
+		}
+
+		#[cfg(feature = "try-runtime")]
+		fn pre_upgrade() -> Result<(), &'static str> {
+			use frame_support::traits::OnRuntimeUpgradeHelpersExt;
+			frame_support::ensure!(
+				StorageVersion::<T>::get() == crate::Releases::V8_0_0,
+				"must upgrade linearly"
+			);
+
+			let prev_count = T::VoterList::count();
+			Self::set_temp_storage(prev_count, "prev");
+			Ok(())
+		}
+
+		#[cfg(feature = "try-runtime")]
+		fn post_upgrade() -> Result<(), &'static str> {
+			use frame_support::traits::OnRuntimeUpgradeHelpersExt;
+			let post_count = T::VoterList::count();
+			let prev_count = Self::get_temp_storage::<u32>("prev").unwrap();
+			let validators = Validators::<T>::count();
+			assert!(post_count == prev_count + validators);
+
+			frame_support::ensure!(
+				StorageVersion::<T>::get() == crate::Releases::V9_0_0,
+				"must upgrade "
+			);
+			Ok(())
+		}
+	}
+}
 
 pub mod v8 {
+	use crate::{Config, Nominators, Pallet, StorageVersion, Weight};
 	use frame_election_provider_support::SortedListProvider;
 	use frame_support::traits::Get;
 
-	use crate::{Config, Nominators, Pallet, StorageVersion, Weight};
-
 	#[cfg(feature = "try-runtime")]
 	pub fn pre_migrate<T: Config>() -> Result<(), &'static str> {
 		frame_support::ensure!(
@@ -35,16 +105,16 @@ pub mod v8 {
 		Ok(())
 	}
 
-	/// Migration to sorted [`SortedListProvider`].
+	/// Migration to sorted `VoterList`.
 	pub fn migrate<T: Config>() -> Weight {
 		if StorageVersion::<T>::get() == crate::Releases::V7_0_0 {
 			crate::log!(info, "migrating staking to Releases::V8_0_0");
 
-			let migrated = T::SortedListProvider::unsafe_regenerate(
+			let migrated = T::VoterList::unsafe_regenerate(
 				Nominators::<T>::iter().map(|(id, _)| id),
 				Pallet::<T>::weight_of_fn(),
 			);
-			debug_assert_eq!(T::SortedListProvider::sanity_check(), Ok(()));
+			debug_assert_eq!(T::VoterList::sanity_check(), Ok(()));
 
 			StorageVersion::<T>::put(crate::Releases::V8_0_0);
 			crate::log!(
@@ -61,8 +131,7 @@ pub mod v8 {
 
 	#[cfg(feature = "try-runtime")]
 	pub fn post_migrate<T: Config>() -> Result<(), &'static str> {
-		T::SortedListProvider::sanity_check()
-			.map_err(|_| "SortedListProvider is not in a sane state.")?;
+		T::VoterList::sanity_check().map_err(|_| "VoterList is not in a sane state.")?;
 		crate::log!(info, "👜 staking bags-list migration passes POST migrate checks ✅",);
 		Ok(())
 	}