Add extrinsic to improve position in a bag of bags-list (#9829)

* pallet-bags-list: Add `put_in_front_of` extrinsic

This PR adds the extrinsic `put_in_front_of` which allows the user to specify a `lighter` and `heavier` account within the same bag. The extrinsic will move `heavier` directly in front of `lighter`.  The parameter names refer to the fact that `lighter` must have a lower `VoteWeight` then `heavier`. 

In the ideal use case, where a user wants to improve the position of their account within a bag, the user would iterate the bag, starting from the head, and find the first node who's `VoteWeight` is less than theirs. They would then supply the `id` of the node as the `lighter` argument and their own `id` as the `heavier` argument.

* Test & Benchmarks

* Respect line width

* Remove List::put_in_fron_of tests; Remove AlreadyHigher error

* The dispatch origin for this call must be ...

* Add some periods

* Add back test to list module: put_in_front_of_exits_early_if_bag_not_found

* add test tests::pallet::heavier_is_head_lighter_is_not_terminal

* Cater for edge case of heavier being head

* Add ExtBuilder::add_aux_data; try to make some tests use simpler data

* Update frame/bags-list/src/list/tests.rs

* make insert_at_unchecked infallible

* Make it permissioned - only callable by heavier

* Add test cases for insert_at_unchecked

* Move counter update to insert_at; fix comments

* Address some feedback

* Make voteweight constructed with parameter_types

* Always set vote weight for Ids in build

* Add skip_genesis_ids

* Do not pass weight fn to List put_in_front_of

* Remove remants of CounterForListNodes

* fmt

* cargo run --quiet --release --features=runtime-benchmarks --manifest-path=bin/node/cli/Cargo.toml -- benchmark --chain=dev --steps=50 --repeat=20 --pallet=pallet_bags_list --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --output=./frame/bags-list/src/weights.rs --template=./.maintain/frame-weight-template.hbs

* Delete messed up weights file

* Some place holder stuff so we can run bench in CI

* Fix

* cargo run --quiet --release --features=runtime-benchmarks --manifest-path=bin/node/cli/Cargo.toml -- benchmark --chain=dev --steps=50 --repeat=20 --pallet=pallet_bags_list --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --output=./frame/bags-list/src/weights.rs --template=./.maintain/frame-weight-template.hbs

* Update frame/bags-list/src/list/mod.rs

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* fmt

* Log + debug assert when refetching an Id

Co-authored-by: Parity Bot <admin@parity.io>
Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

substrate/frame/bags-list/src/benchmarks.rs

@@ -19,7 +19,7 @@
 
 use super::*;
 use crate::list::List;
-use frame_benchmarking::{account, whitelisted_caller};
+use frame_benchmarking::{account, whitelist_account, whitelisted_caller};
 use frame_election_provider_support::VoteWeightProvider;
 use frame_support::{assert_ok, traits::Get};
 use frame_system::RawOrigin as SystemOrigin;
@@ -137,9 +137,41 @@ frame_benchmarking::benchmarks! {
 		);
 	}
 
-	impl_benchmark_test_suite!(
-		Pallet,
-		crate::mock::ExtBuilder::default().build(),
-		crate::mock::Runtime,
-	)
+	put_in_front_of {
+		// The most expensive case for `put_in_front_of`:
+		//
+		// - both heavier's `prev` and `next` are nodes that will need to be read and written.
+		// - `lighter` is the bag's `head`, so the bag will need to be read and written.
+
+		let bag_thresh = T::BagThresholds::get()[0];
+
+		// insert the nodes in order
+		let lighter: T::AccountId = account("lighter", 0, 0);
+		assert_ok!(List::<T>::insert(lighter.clone(), bag_thresh));
+
+		let heavier_prev: T::AccountId = account("heavier_prev", 0, 0);
+		assert_ok!(List::<T>::insert(heavier_prev.clone(), bag_thresh));
+
+		let heavier: T::AccountId = account("heavier", 0, 0);
+		assert_ok!(List::<T>::insert(heavier.clone(), bag_thresh));
+
+		let heavier_next: T::AccountId = account("heavier_next", 0, 0);
+		assert_ok!(List::<T>::insert(heavier_next.clone(), bag_thresh));
+
+		T::VoteWeightProvider::set_vote_weight_of(&lighter, bag_thresh - 1);
+		T::VoteWeightProvider::set_vote_weight_of(&heavier, bag_thresh);
+
+		assert_eq!(
+			List::<T>::iter().map(|n| n.id().clone()).collect::<Vec<_>>(),
+			vec![lighter.clone(), heavier_prev.clone(), heavier.clone(), heavier_next.clone()]
+		);
+
+		whitelist_account!(heavier);
+	}: _(SystemOrigin::Signed(heavier.clone()), lighter.clone())
+	verify {
+		assert_eq!(
+			List::<T>::iter().map(|n| n.id().clone()).collect::<Vec<_>>(),
+			vec![heavier, lighter, heavier_prev, heavier_next]
+		)
+	}
 }

substrate/frame/bags-list/src/lib.rs

@@ -173,6 +173,17 @@ pub mod pallet {
 		Rebagged { who: T::AccountId, from: VoteWeight, to: VoteWeight },
 	}
 
+	#[pallet::error]
+	#[cfg_attr(test, derive(PartialEq))]
+	pub enum Error<T> {
+		/// Attempted to place node in front of a node in another bag.
+		NotInSameBag,
+		/// Id not found in list.
+		IdNotFound,
+		/// An Id does not have a greater vote weight than another Id.
+		NotHeavier,
+	}
+
 	#[pallet::call]
 	impl<T: Config> Pallet<T> {
 		/// Declare that some `dislocated` account has, through rewards or penalties, sufficiently
@@ -190,6 +201,20 @@ pub mod pallet {
 			let _ = Pallet::<T>::do_rebag(&dislocated, current_weight);
 			Ok(())
 		}
+
+		/// Move the caller's Id directly in front of `lighter`.
+		///
+		/// The dispatch origin for this call must be _Signed_ and can only be called by the Id of
+		/// the account going in front of `lighter`.
+		///
+		/// Only works if
+		/// - both nodes are within the same bag,
+		/// - and `origin` has a greater `VoteWeight` than `lighter`.
+		#[pallet::weight(T::WeightInfo::put_in_front_of())]
+		pub fn put_in_front_of(origin: OriginFor<T>, lighter: T::AccountId) -> DispatchResult {
+			let heavier = ensure_signed(origin)?;
+			List::<T>::put_in_front_of(&lighter, &heavier).map_err(Into::into)
+		}
 	}
 
 	#[pallet::hooks]

substrate/frame/bags-list/src/list/mod.rs

@@ -376,6 +376,84 @@ impl<T: Config> List<T> {
 		})
 	}
 
+	/// Put `heavier_id` to the position directly in front of `lighter_id`. Both ids must be in the
+	/// same bag and the `weight_of` `lighter_id` must be less than that of `heavier_id`.
+	pub(crate) fn put_in_front_of(
+		lighter_id: &T::AccountId,
+		heavier_id: &T::AccountId,
+	) -> Result<(), crate::pallet::Error<T>> {
+		use crate::pallet;
+		use frame_support::ensure;
+
+		let lighter_node = Node::<T>::get(&lighter_id).ok_or(pallet::Error::IdNotFound)?;
+		let heavier_node = Node::<T>::get(&heavier_id).ok_or(pallet::Error::IdNotFound)?;
+
+		ensure!(lighter_node.bag_upper == heavier_node.bag_upper, pallet::Error::NotInSameBag);
+
+		// this is the most expensive check, so we do it last.
+		ensure!(
+			T::VoteWeightProvider::vote_weight(&heavier_id) >
+				T::VoteWeightProvider::vote_weight(&lighter_id),
+			pallet::Error::NotHeavier
+		);
+
+		// remove the heavier node from this list. Note that this removes the node from storage and
+		// decrements the node counter.
+		Self::remove(&heavier_id);
+
+		// re-fetch `lighter_node` from storage since it may have been updated when `heavier_node`
+		// was removed.
+		let lighter_node = Node::<T>::get(&lighter_id).ok_or_else(|| {
+			debug_assert!(false, "id that should exist cannot be found");
+			crate::log!(warn, "id that should exist cannot be found");
+			pallet::Error::IdNotFound
+		})?;
+
+		// insert `heavier_node` directly in front of `lighter_node`. This will update both nodes
+		// in storage and update the node counter.
+		Self::insert_at_unchecked(lighter_node, heavier_node);
+
+		Ok(())
+	}
+
+	/// Insert `node` directly in front of `at`.
+	///
+	/// WARNINGS:
+	/// - this is a naive function in that it does not check if `node` belongs to the same bag as
+	/// `at`. It is expected that the call site will check preconditions.
+	/// - this will panic if `at.bag_upper` is not a bag that already exists in storage.
+	fn insert_at_unchecked(mut at: Node<T>, mut node: Node<T>) {
+		// connect `node` to its new `prev`.
+		node.prev = at.prev.clone();
+		if let Some(mut prev) = at.prev() {
+			prev.next = Some(node.id().clone());
+			prev.put()
+		}
+
+		// connect `node` and `at`.
+		node.next = Some(at.id().clone());
+		at.prev = Some(node.id().clone());
+
+		if node.is_terminal() {
+			// `node` is the new head, so we make sure the bag is updated. Note,
+			// since `node` is always in front of `at` we know that 1) there is always at least 2
+			// nodes in the bag, and 2) only `node` could be the head and only `at` could be the
+			// tail.
+			let mut bag = Bag::<T>::get(at.bag_upper)
+				.expect("given nodes must always have a valid bag. qed.");
+
+			if node.prev == None {
+				bag.head = Some(node.id().clone())
+			}
+
+			bag.put()
+		};
+
+		// write the updated nodes to storage.
+		at.put();
+		node.put();
+	}
+
 	/// Sanity check the list.
 	///
 	/// This should be called from the call-site, whenever one of the mutating apis (e.g. `insert`)

substrate/frame/bags-list/src/list/tests.rs

@@ -383,6 +383,123 @@ mod list {
 			assert!(non_existent_ids.iter().all(|id| !List::<Runtime>::contains(id)));
 		})
 	}
+
+	#[test]
+	#[should_panic = "given nodes must always have a valid bag. qed."]
+	fn put_in_front_of_panics_if_bag_not_found() {
+		ExtBuilder::default().skip_genesis_ids().build_and_execute_no_post_check(|| {
+			let node_10_no_bag = Node::<Runtime> { id: 10, prev: None, next: None, bag_upper: 15 };
+			let node_11_no_bag = Node::<Runtime> { id: 11, prev: None, next: None, bag_upper: 15 };
+
+			// given
+			ListNodes::<Runtime>::insert(10, node_10_no_bag);
+			ListNodes::<Runtime>::insert(11, node_11_no_bag);
+			StakingMock::set_vote_weight_of(&10, 14);
+			StakingMock::set_vote_weight_of(&11, 15);
+			assert!(!ListBags::<Runtime>::contains_key(15));
+			assert_eq!(List::<Runtime>::get_bags(), vec![]);
+
+			// then .. this panics
+			let _ = List::<Runtime>::put_in_front_of(&10, &11);
+		});
+	}
+
+	#[test]
+	fn insert_at_unchecked_at_is_only_node() {
+		// Note that this `insert_at_unchecked` test should fail post checks because node 42 does
+		// not get re-assigned the correct bagu pper. This is because `insert_at_unchecked` assumes
+		// both nodes are already in the same bag with the correct bag upper.
+		ExtBuilder::default().build_and_execute_no_post_check(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			// implicitly also test that `node`'s `prev`/`next` are correctly re-assigned.
+			let node_42 =
+				Node::<Runtime> { id: 42, prev: Some(1), next: Some(2), bag_upper: 1_000 };
+			assert!(!crate::ListNodes::<Runtime>::contains_key(42));
+
+			let node_1 = crate::ListNodes::<Runtime>::get(&1).unwrap();
+
+			// when
+			List::<Runtime>::insert_at_unchecked(node_1, node_42);
+
+			// then
+			assert_eq!(
+				List::<Runtime>::get_bags(),
+				vec![(10, vec![42, 1]), (1_000, vec![2, 3, 4])]
+			);
+		})
+	}
+
+	#[test]
+	fn insert_at_unchecked_at_is_head() {
+		ExtBuilder::default().build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			// implicitly also test that `node`'s `prev`/`next` are correctly re-assigned.
+			let node_42 = Node::<Runtime> { id: 42, prev: Some(4), next: None, bag_upper: 1_000 };
+			assert!(!crate::ListNodes::<Runtime>::contains_key(42));
+
+			let node_2 = crate::ListNodes::<Runtime>::get(&2).unwrap();
+
+			// when
+			List::<Runtime>::insert_at_unchecked(node_2, node_42);
+
+			// then
+			assert_eq!(
+				List::<Runtime>::get_bags(),
+				vec![(10, vec![1]), (1_000, vec![42, 2, 3, 4])]
+			);
+		})
+	}
+
+	#[test]
+	fn insert_at_unchecked_at_is_non_terminal() {
+		ExtBuilder::default().build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			// implicitly also test that `node`'s `prev`/`next` are correctly re-assigned.
+			let node_42 = Node::<Runtime> { id: 42, prev: None, next: Some(2), bag_upper: 1_000 };
+			assert!(!crate::ListNodes::<Runtime>::contains_key(42));
+
+			let node_3 = crate::ListNodes::<Runtime>::get(&3).unwrap();
+
+			// when
+			List::<Runtime>::insert_at_unchecked(node_3, node_42);
+
+			// then
+			assert_eq!(
+				List::<Runtime>::get_bags(),
+				vec![(10, vec![1]), (1_000, vec![2, 42, 3, 4])]
+			);
+		})
+	}
+
+	#[test]
+	fn insert_at_unchecked_at_is_tail() {
+		ExtBuilder::default().build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			// implicitly also test that `node`'s `prev`/`next` are correctly re-assigned.
+			let node_42 =
+				Node::<Runtime> { id: 42, prev: Some(42), next: Some(42), bag_upper: 1_000 };
+			assert!(!crate::ListNodes::<Runtime>::contains_key(42));
+
+			let node_4 = crate::ListNodes::<Runtime>::get(&4).unwrap();
+
+			// when
+			List::<Runtime>::insert_at_unchecked(node_4, node_42);
+
+			// then
+			assert_eq!(
+				List::<Runtime>::get_bags(),
+				vec![(10, vec![1]), (1_000, vec![2, 3, 42, 4])]
+			);
+		})
+	}
 }
 
 mod bags {

substrate/frame/bags-list/src/mock.rs

@@ -21,28 +21,26 @@ use super::*;
 use crate::{self as bags_list};
 use frame_election_provider_support::VoteWeight;
 use frame_support::parameter_types;
+use std::collections::HashMap;
 
 pub type AccountId = u32;
 pub type Balance = u32;
 
 parameter_types! {
+	// Set the vote weight for any id who's weight has _not_ been set with `set_vote_weight_of`.
 	pub static NextVoteWeight: VoteWeight = 0;
+	pub static NextVoteWeightMap: HashMap<AccountId, VoteWeight> = Default::default();
 }
 
 pub struct StakingMock;
 impl frame_election_provider_support::VoteWeightProvider<AccountId> for StakingMock {
 	fn vote_weight(id: &AccountId) -> VoteWeight {
-		match id {
-			710 => 15,
-			711 => 16,
-			712 => 2_000, // special cases used for migrate test
-			_ => NextVoteWeight::get(),
-		}
+		*NextVoteWeightMap::get().get(id).unwrap_or(&NextVoteWeight::get())
 	}
+
 	#[cfg(any(feature = "runtime-benchmarks", test))]
-	fn set_vote_weight_of(_: &AccountId, weight: VoteWeight) {
-		// we don't really keep a mapping, just set weight for everyone.
-		NextVoteWeight::set(weight)
+	fn set_vote_weight_of(id: &AccountId, weight: VoteWeight) {
+		NEXT_VOTE_WEIGHT_MAP.with(|m| m.borrow_mut().insert(id.clone(), weight));
 	}
 }
 
@@ -103,9 +101,17 @@ pub(crate) const GENESIS_IDS: [(AccountId, VoteWeight); 4] =
 #[derive(Default)]
 pub struct ExtBuilder {
 	ids: Vec<(AccountId, VoteWeight)>,
+	skip_genesis_ids: bool,
 }
 
 impl ExtBuilder {
+	/// Skip adding the default genesis ids to the list.
+	#[cfg(test)]
+	pub(crate) fn skip_genesis_ids(mut self) -> Self {
+		self.skip_genesis_ids = true;
+		self
+	}
+
 	/// Add some AccountIds to insert into `List`.
 	#[cfg(test)]
 	pub(crate) fn add_ids(mut self, ids: Vec<(AccountId, VoteWeight)>) -> Self {
@@ -117,10 +123,17 @@ impl ExtBuilder {
 		sp_tracing::try_init_simple();
 		let storage = frame_system::GenesisConfig::default().build_storage::<Runtime>().unwrap();
 
+		let ids_with_weight: Vec<_> = if self.skip_genesis_ids {
+			self.ids.iter().collect()
+		} else {
+			GENESIS_IDS.iter().chain(self.ids.iter()).collect()
+		};
+
 		let mut ext = sp_io::TestExternalities::from(storage);
 		ext.execute_with(|| {
-			for (id, weight) in GENESIS_IDS.iter().chain(self.ids.iter()) {
+			for (id, weight) in ids_with_weight {
 				frame_support::assert_ok!(List::<Runtime>::insert(*id, *weight));
+				StakingMock::set_vote_weight_of(id, *weight);
 			}
 		});
 

substrate/frame/bags-list/src/tests.rs

@@ -15,7 +15,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use frame_support::{assert_ok, assert_storage_noop, traits::IntegrityTest};
+use frame_support::{assert_noop, assert_ok, assert_storage_noop, traits::IntegrityTest};
 
 use super::*;
 use frame_election_provider_support::SortedListProvider;
@@ -35,7 +35,7 @@ mod pallet {
 			);
 
 			// when increasing vote weight to the level of non-existent bag
-			NextVoteWeight::set(2_000);
+			StakingMock::set_vote_weight_of(&42, 2_000);
 			assert_ok!(BagsList::rebag(Origin::signed(0), 42));
 
 			// then a new bag is created and the id moves into it
@@ -45,7 +45,7 @@ mod pallet {
 			);
 
 			// when decreasing weight within the range of the current bag
-			NextVoteWeight::set(1001);
+			StakingMock::set_vote_weight_of(&42, 1_001);
 			assert_ok!(BagsList::rebag(Origin::signed(0), 42));
 
 			// then the id does not move
@@ -55,7 +55,7 @@ mod pallet {
 			);
 
 			// when reducing weight to the level of a non-existent bag
-			NextVoteWeight::set(30);
+			StakingMock::set_vote_weight_of(&42, 30);
 			assert_ok!(BagsList::rebag(Origin::signed(0), 42));
 
 			// then a new bag is created and the id moves into it
@@ -65,7 +65,7 @@ mod pallet {
 			);
 
 			// when increasing weight to the level of a pre-existing bag
-			NextVoteWeight::set(500);
+			StakingMock::set_vote_weight_of(&42, 500);
 			assert_ok!(BagsList::rebag(Origin::signed(0), 42));
 
 			// then the id moves into that bag
@@ -85,7 +85,7 @@ mod pallet {
 			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
 
 			// when
-			NextVoteWeight::set(10);
+			StakingMock::set_vote_weight_of(&4, 10);
 			assert_ok!(BagsList::rebag(Origin::signed(0), 4));
 
 			// then
@@ -93,6 +93,7 @@ mod pallet {
 			assert_eq!(Bag::<Runtime>::get(1_000).unwrap(), Bag::new(Some(2), Some(3), 1_000));
 
 			// when
+			StakingMock::set_vote_weight_of(&3, 10);
 			assert_ok!(BagsList::rebag(Origin::signed(0), 3));
 
 			// then
@@ -103,6 +104,7 @@ mod pallet {
 			assert_eq!(get_list_as_ids(), vec![2u32, 1, 4, 3]);
 
 			// when
+			StakingMock::set_vote_weight_of(&2, 10);
 			assert_ok!(BagsList::rebag(Origin::signed(0), 2));
 
 			// then
@@ -117,7 +119,7 @@ mod pallet {
 	fn rebag_head_works() {
 		ExtBuilder::default().build_and_execute(|| {
 			// when
-			NextVoteWeight::set(10);
+			StakingMock::set_vote_weight_of(&2, 10);
 			assert_ok!(BagsList::rebag(Origin::signed(0), 2));
 
 			// then
@@ -125,6 +127,7 @@ mod pallet {
 			assert_eq!(Bag::<Runtime>::get(1_000).unwrap(), Bag::new(Some(3), Some(4), 1_000));
 
 			// when
+			StakingMock::set_vote_weight_of(&3, 10);
 			assert_ok!(BagsList::rebag(Origin::signed(0), 3));
 
 			// then
@@ -132,6 +135,7 @@ mod pallet {
 			assert_eq!(Bag::<Runtime>::get(1_000).unwrap(), Bag::new(Some(4), Some(4), 1_000));
 
 			// when
+			StakingMock::set_vote_weight_of(&4, 10);
 			assert_ok!(BagsList::rebag(Origin::signed(0), 4));
 
 			// then
@@ -196,6 +200,249 @@ mod pallet {
 			assert_storage_noop!(assert!(BagsList::rebag(Origin::signed(0), 10).is_ok()));
 		})
 	}
+
+	#[test]
+	fn put_in_front_of_two_node_bag_heavier_is_tail() {
+		ExtBuilder::default()
+			.skip_genesis_ids()
+			.add_ids(vec![(10, 15), (11, 16)])
+			.build_and_execute(|| {
+				// given
+				assert_eq!(List::<Runtime>::get_bags(), vec![(20, vec![10, 11])]);
+
+				// when
+				assert_ok!(BagsList::put_in_front_of(Origin::signed(11), 10));
+
+				// then
+				assert_eq!(List::<Runtime>::get_bags(), vec![(20, vec![11, 10])]);
+			});
+	}
+
+	#[test]
+	fn put_in_front_of_two_node_bag_heavier_is_head() {
+		ExtBuilder::default()
+			.skip_genesis_ids()
+			.add_ids(vec![(11, 16), (10, 15)])
+			.build_and_execute(|| {
+				// given
+				assert_eq!(List::<Runtime>::get_bags(), vec![(20, vec![11, 10])]);
+
+				// when
+				assert_ok!(BagsList::put_in_front_of(Origin::signed(11), 10));
+
+				// then
+				assert_eq!(List::<Runtime>::get_bags(), vec![(20, vec![11, 10])]);
+			});
+	}
+
+	#[test]
+	fn put_in_front_of_non_terminal_nodes_heavier_behind() {
+		ExtBuilder::default().add_ids(vec![(5, 1_000)]).build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4, 5])]);
+
+			StakingMock::set_vote_weight_of(&3, 999);
+
+			// when
+			assert_ok!(BagsList::put_in_front_of(Origin::signed(4), 3));
+
+			// then
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 4, 3, 5])]);
+		});
+	}
+
+	#[test]
+	fn put_in_front_of_non_terminal_nodes_heavier_in_front() {
+		ExtBuilder::default()
+			.add_ids(vec![(5, 1_000), (6, 1_000)])
+			.build_and_execute(|| {
+				// given
+				assert_eq!(
+					List::<Runtime>::get_bags(),
+					vec![(10, vec![1]), (1_000, vec![2, 3, 4, 5, 6])]
+				);
+
+				StakingMock::set_vote_weight_of(&5, 999);
+
+				// when
+				assert_ok!(BagsList::put_in_front_of(Origin::signed(3), 5));
+
+				// then
+				assert_eq!(
+					List::<Runtime>::get_bags(),
+					vec![(10, vec![1]), (1_000, vec![2, 4, 3, 5, 6])]
+				);
+			});
+	}
+
+	#[test]
+	fn put_in_front_of_lighter_is_head_heavier_is_non_terminal() {
+		ExtBuilder::default().build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			StakingMock::set_vote_weight_of(&2, 999);
+
+			// when
+			assert_ok!(BagsList::put_in_front_of(Origin::signed(3), 2));
+
+			// then
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![3, 2, 4])]);
+		});
+	}
+
+	#[test]
+	fn put_in_front_of_heavier_is_tail_lighter_is_non_terminal() {
+		ExtBuilder::default().build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			StakingMock::set_vote_weight_of(&3, 999);
+
+			// when
+			assert_ok!(BagsList::put_in_front_of(Origin::signed(4), 3));
+
+			// then
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 4, 3])]);
+		});
+	}
+
+	#[test]
+	fn put_in_front_of_heavier_is_tail_lighter_is_head() {
+		ExtBuilder::default().add_ids(vec![(5, 1_000)]).build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4, 5])]);
+
+			StakingMock::set_vote_weight_of(&2, 999);
+
+			// when
+			assert_ok!(BagsList::put_in_front_of(Origin::signed(5), 2));
+
+			// then
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![5, 2, 3, 4])]);
+		});
+	}
+
+	#[test]
+	fn put_in_front_of_heavier_is_head_lighter_is_not_terminal() {
+		ExtBuilder::default().add_ids(vec![(5, 1_000)]).build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4, 5])]);
+
+			StakingMock::set_vote_weight_of(&4, 999);
+
+			// when
+			BagsList::put_in_front_of(Origin::signed(2), 4).unwrap();
+
+			// then
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![3, 2, 4, 5])]);
+		});
+	}
+
+	#[test]
+	fn put_in_front_of_lighter_is_tail_heavier_is_not_terminal() {
+		ExtBuilder::default().add_ids(vec![(5, 900)]).build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4, 5])]);
+
+			// when
+			BagsList::put_in_front_of(Origin::signed(3), 5).unwrap();
+
+			// then
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 4, 3, 5])]);
+		});
+	}
+
+	#[test]
+	fn put_in_front_of_lighter_is_tail_heavier_is_head() {
+		ExtBuilder::default().build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			StakingMock::set_vote_weight_of(&4, 999);
+
+			// when
+			BagsList::put_in_front_of(Origin::signed(2), 4).unwrap();
+
+			// then
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![3, 2, 4])]);
+		});
+	}
+
+	#[test]
+	fn put_in_front_of_errors_if_heavier_is_less_than_lighter() {
+		ExtBuilder::default().build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			StakingMock::set_vote_weight_of(&3, 999);
+
+			// then
+			assert_noop!(
+				BagsList::put_in_front_of(Origin::signed(3), 2),
+				crate::pallet::Error::<Runtime>::NotHeavier
+			);
+		});
+	}
+
+	#[test]
+	fn put_in_front_of_errors_if_heavier_is_equal_weight_to_lighter() {
+		ExtBuilder::default().build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			// then
+			assert_noop!(
+				BagsList::put_in_front_of(Origin::signed(3), 4),
+				crate::pallet::Error::<Runtime>::NotHeavier
+			);
+		});
+	}
+
+	#[test]
+	fn put_in_front_of_errors_if_nodes_not_found() {
+		// `heavier` not found
+		ExtBuilder::default().build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			assert!(!ListNodes::<Runtime>::contains_key(5));
+
+			// then
+			assert_noop!(
+				BagsList::put_in_front_of(Origin::signed(5), 4),
+				crate::pallet::Error::<Runtime>::IdNotFound
+			);
+		});
+
+		// `lighter` not found
+		ExtBuilder::default().build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			assert!(!ListNodes::<Runtime>::contains_key(5));
+
+			// then
+			assert_noop!(
+				BagsList::put_in_front_of(Origin::signed(4), 5),
+				crate::pallet::Error::<Runtime>::IdNotFound
+			);
+		});
+	}
+
+	#[test]
+	fn put_in_front_of_errors_if_nodes_not_in_same_bag() {
+		ExtBuilder::default().build_and_execute(|| {
+			// given
+			assert_eq!(List::<Runtime>::get_bags(), vec![(10, vec![1]), (1_000, vec![2, 3, 4])]);
+
+			// then
+			assert_noop!(
+				BagsList::put_in_front_of(Origin::signed(4), 1),
+				crate::pallet::Error::<Runtime>::NotInSameBag
+			);
+		});
+	}
 }
 
 mod sorted_list_provider {

substrate/frame/bags-list/src/weights.rs

@@ -18,7 +18,7 @@
 //! Autogenerated weights for pallet_bags_list
 //!
 //! THIS FILE WAS AUTO-GENERATED USING THE SUBSTRATE BENCHMARK CLI VERSION 4.0.0-dev
-//! DATE: 2021-09-15, STEPS: `50`, REPEAT: 20, LOW RANGE: `[]`, HIGH RANGE: `[]`
+//! DATE: 2021-11-18, STEPS: `50`, REPEAT: 20, LOW RANGE: `[]`, HIGH RANGE: `[]`
 //! EXECUTION: Some(Wasm), WASM-EXECUTION: Compiled, CHAIN: Some("dev"), DB CACHE: 128
 
 // Executed Command:
@@ -35,7 +35,6 @@
 // --output=./frame/bags-list/src/weights.rs
 // --template=./.maintain/frame-weight-template.hbs
 
-
 #![cfg_attr(rustfmt, rustfmt_skip)]
 #![allow(unused_parens)]
 #![allow(unused_imports)]
@@ -47,6 +46,7 @@ use sp_std::marker::PhantomData;
 pub trait WeightInfo {
 	fn rebag_non_terminal() -> Weight;
 	fn rebag_terminal() -> Weight;
+	fn put_in_front_of() -> Weight;
 }
 
 /// Weights for pallet_bags_list using the Substrate node and recommended hardware.
@@ -57,7 +57,7 @@ impl<T: frame_system::Config> WeightInfo for SubstrateWeight<T> {
 	// Storage: BagsList ListNodes (r:4 w:4)
 	// Storage: BagsList ListBags (r:1 w:1)
 	fn rebag_non_terminal() -> Weight {
-		(74_175_000 as Weight)
+		(70_481_000 as Weight)
 			.saturating_add(T::DbWeight::get().reads(7 as Weight))
 			.saturating_add(T::DbWeight::get().writes(5 as Weight))
 	}
@@ -66,10 +66,20 @@ impl<T: frame_system::Config> WeightInfo for SubstrateWeight<T> {
 	// Storage: BagsList ListNodes (r:3 w:3)
 	// Storage: BagsList ListBags (r:2 w:2)
 	fn rebag_terminal() -> Weight {
-		(73_305_000 as Weight)
+		(68_642_000 as Weight)
 			.saturating_add(T::DbWeight::get().reads(7 as Weight))
 			.saturating_add(T::DbWeight::get().writes(5 as Weight))
 	}
+	// Storage: BagsList ListNodes (r:4 w:4)
+	// Storage: Staking Bonded (r:2 w:0)
+	// Storage: Staking Ledger (r:2 w:0)
+	// Storage: BagsList CounterForListNodes (r:1 w:1)
+	// Storage: BagsList ListBags (r:1 w:1)
+	fn put_in_front_of() -> Weight {
+		(82_341_000 as Weight)
+			.saturating_add(T::DbWeight::get().reads(10 as Weight))
+			.saturating_add(T::DbWeight::get().writes(6 as Weight))
+	}
 }
 
 // For backwards compatibility and tests
@@ -79,7 +89,7 @@ impl WeightInfo for () {
 	// Storage: BagsList ListNodes (r:4 w:4)
 	// Storage: BagsList ListBags (r:1 w:1)
 	fn rebag_non_terminal() -> Weight {
-		(74_175_000 as Weight)
+		(70_481_000 as Weight)
 			.saturating_add(RocksDbWeight::get().reads(7 as Weight))
 			.saturating_add(RocksDbWeight::get().writes(5 as Weight))
 	}
@@ -88,8 +98,18 @@ impl WeightInfo for () {
 	// Storage: BagsList ListNodes (r:3 w:3)
 	// Storage: BagsList ListBags (r:2 w:2)
 	fn rebag_terminal() -> Weight {
-		(73_305_000 as Weight)
+		(68_642_000 as Weight)
 			.saturating_add(RocksDbWeight::get().reads(7 as Weight))
 			.saturating_add(RocksDbWeight::get().writes(5 as Weight))
 	}
+	// Storage: BagsList ListNodes (r:4 w:4)
+	// Storage: Staking Bonded (r:2 w:0)
+	// Storage: Staking Ledger (r:2 w:0)
+	// Storage: BagsList CounterForListNodes (r:1 w:1)
+	// Storage: BagsList ListBags (r:1 w:1)
+	fn put_in_front_of() -> Weight {
+		(82_341_000 as Weight)
+			.saturating_add(RocksDbWeight::get().reads(10 as Weight))
+			.saturating_add(RocksDbWeight::get().writes(6 as Weight))
+	}
 }