Use proper bounded vector type for nominations (#10601)

* Use proper bounded vector type for nominations

* add docs and tweak chill_other for cleanup purposes

* Fix the build

* remove TODO

* add a bit more doc

* even more docs
gushc

* Update frame/staking/src/pallet/mod.rs

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

* Update frame/staking/src/pallet/mod.rs

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

* Fix the nasty bug

* also bound the Snapshot type

* fix doc test

* document bounded_vec

* self-review

* remove unused

* Fix build

* frame-support: repetition overload for bounded_vec

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* fix

* remove the need to allocate into unbounded voters etc etc

* Don't expect

* unbreal the build again

* handle macro a bit better

Co-authored-by: Zeke Mostov <z.mostov@gmail.com>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/frame/staking/src/tests.rs

@@ -4248,7 +4248,11 @@ fn count_check_works() {
 		Validators::<Test>::insert(987654321, ValidatorPrefs::default());
 		Nominators::<Test>::insert(
 			987654321,
-			Nominations { targets: vec![], submitted_in: Default::default(), suppressed: false },
+			Nominations {
+				targets: Default::default(),
+				submitted_in: Default::default(),
+				suppressed: false,
+			},
 		);
 	})
 }
@@ -4589,6 +4593,100 @@ fn min_commission_works() {
 	})
 }
 
+#[test]
+fn change_of_max_nominations() {
+	use frame_election_provider_support::ElectionDataProvider;
+	ExtBuilder::default()
+		.add_staker(60, 61, 10, StakerStatus::Nominator(vec![1]))
+		.add_staker(70, 71, 10, StakerStatus::Nominator(vec![1, 2, 3]))
+		.balance_factor(10)
+		.build_and_execute(|| {
+			// pre-condition
+			assert_eq!(MaxNominations::get(), 16);
+
+			assert_eq!(
+				Nominators::<Test>::iter()
+					.map(|(k, n)| (k, n.targets.len()))
+					.collect::<Vec<_>>(),
+				vec![(70, 3), (101, 2), (60, 1)]
+			);
+			// 3 validators and 3 nominators
+			assert_eq!(Staking::voters(None).unwrap().len(), 3 + 3);
+
+			// abrupt change from 16 to 4, everyone should be fine.
+			MaxNominations::set(4);
+
+			assert_eq!(
+				Nominators::<Test>::iter()
+					.map(|(k, n)| (k, n.targets.len()))
+					.collect::<Vec<_>>(),
+				vec![(70, 3), (101, 2), (60, 1)]
+			);
+			assert_eq!(Staking::voters(None).unwrap().len(), 3 + 3);
+
+			// abrupt change from 4 to 3, everyone should be fine.
+			MaxNominations::set(3);
+
+			assert_eq!(
+				Nominators::<Test>::iter()
+					.map(|(k, n)| (k, n.targets.len()))
+					.collect::<Vec<_>>(),
+				vec![(70, 3), (101, 2), (60, 1)]
+			);
+			assert_eq!(Staking::voters(None).unwrap().len(), 3 + 3);
+
+			// abrupt change from 3 to 2, this should cause some nominators to be non-decodable, and
+			// thus non-existent unless if they update.
+			MaxNominations::set(2);
+
+			assert_eq!(
+				Nominators::<Test>::iter()
+					.map(|(k, n)| (k, n.targets.len()))
+					.collect::<Vec<_>>(),
+				vec![(101, 2), (60, 1)]
+			);
+			// 70 is still in storage..
+			assert!(Nominators::<Test>::contains_key(70));
+			// but its value cannot be decoded and default is returned.
+			assert!(Nominators::<Test>::get(70).is_none());
+
+			assert_eq!(Staking::voters(None).unwrap().len(), 3 + 2);
+			assert!(Nominators::<Test>::contains_key(101));
+
+			// abrupt change from 2 to 1, this should cause some nominators to be non-decodable, and
+			// thus non-existent unless if they update.
+			MaxNominations::set(1);
+
+			assert_eq!(
+				Nominators::<Test>::iter()
+					.map(|(k, n)| (k, n.targets.len()))
+					.collect::<Vec<_>>(),
+				vec![(60, 1)]
+			);
+			assert!(Nominators::<Test>::contains_key(70));
+			assert!(Nominators::<Test>::contains_key(60));
+			assert!(Nominators::<Test>::get(70).is_none());
+			assert!(Nominators::<Test>::get(60).is_some());
+			assert_eq!(Staking::voters(None).unwrap().len(), 3 + 1);
+
+			// now one of them can revive themselves by re-nominating to a proper value.
+			assert_ok!(Staking::nominate(Origin::signed(71), vec![1]));
+			assert_eq!(
+				Nominators::<Test>::iter()
+					.map(|(k, n)| (k, n.targets.len()))
+					.collect::<Vec<_>>(),
+				vec![(70, 1), (60, 1)]
+			);
+
+			// or they can be chilled by any account.
+			assert!(Nominators::<Test>::contains_key(101));
+			assert!(Nominators::<Test>::get(101).is_none());
+			assert_ok!(Staking::chill_other(Origin::signed(70), 100));
+			assert!(!Nominators::<Test>::contains_key(101));
+			assert!(Nominators::<Test>::get(101).is_none());
+		})
+}
+
 mod sorted_list_provider {
 	use super::*;
 	use frame_election_provider_support::SortedListProvider;