no collator shall be left unpaid

pallets/parachain-staking/src/lib.rs

@@ -2917,7 +2917,33 @@ pub mod pallet {
 
 			let old_round = round - 1;
 			// Get total collator staking number of round that is ending
-			let (in_reads, total_stake) = Self::get_total_collator_staking_num(old_round);
+			let (in_reads, mut total_stake) = Self::get_total_collator_staking_num(old_round);
+
+			// Total stake cannot be zero if there are any authors noted for previous round.
+			// We expect this is the case when runtime upgrade for token-economy-v2 is done.
+			// As there was no snapshot for the collators of that round.
+			// TODO this case can be removed in later upgrades, after token-economy-v2 is installed.
+			if total_stake.is_zero() {
+				// there will be only 1 unfortunate author, as we force new round in runtime
+				// upgrade. But we iterate through all possible entities just in case.
+				CollatorBlocks::<T>::iter_prefix(old_round).for_each(|(collator, num)| {
+					// get author's state
+					if let Some(state) = CandidatePool::<T>::get(collator.clone()) {
+						let collator_total = T::CurrencyBalance::from(num)
+							.checked_mul(&state.total)
+							.unwrap_or_else(Zero::zero);
+						// calculate total stake in session
+						total_stake = total_stake.saturating_add(collator_total);
+						reads = reads.saturating_add(Weight::from_parts(1_u64, 0));
+
+						// snapshot these collators
+						AtStake::<T>::insert(old_round, collator, state);
+						writes = writes.saturating_add(Weight::from_parts(1_u64, 0));
+					};
+					reads = reads.saturating_add(Weight::from_parts(1_u64, 0));
+				});
+			}
+
 			// Get total issuance of round that is ending
 			let (issuance_weight, total_issuance) = Self::pot_issuance();
 			reads = reads.saturating_add(in_reads).saturating_add(issuance_weight);

pallets/parachain-staking/src/migrations.rs

@@ -2,15 +2,13 @@
 
 use crate::{
 	pallet::{Config, Pallet, OLD_STAKING_ID, STAKING_ID},
-	types::{AccountIdOf, Candidate, OldCandidate},
+	types::{Candidate, OldCandidate},
 	CandidatePool, ForceNewRound, Round,
 };
 use frame_support::{
-	pallet_prelude::{GetStorageVersion, StorageVersion, ValueQuery},
-	storage_alias,
+	pallet_prelude::{GetStorageVersion, StorageVersion},
 	traits::{Get, LockableCurrency, WithdrawReasons},
 	weights::Weight,
-	Twox64Concat,
 };
 use pallet_balances::Locks;
 use sp_runtime::Permill;
@@ -34,9 +32,6 @@ mod upgrade {
 
 	use super::*;
 
-	#[storage_alias]
-	type CollatorBlock<T: Config> =
-		StorageMap<Pallet<T>, Twox64Concat, AccountIdOf<T>, u32, ValueQuery>;
 	/// Migration implementation that deletes the old reward rate config and changes the staking ID.
 	pub struct Migrate<T>(sp_std::marker::PhantomData<T>);