staking-async: add missing new_session_genesis

prdoc/pr_8310.prdoc

@@ -0,0 +1,19 @@
+title: 'staking-async: add missing new_session_genesis'
+doc:
+  - audience: Runtime Dev
+    description: |-
+      Fix issue #8302 as introduced by #8127 where the staking-async module could fail during genesis.
+      The issue was related to the staking-async module in the Polkadot SDK, specifically with the implementation of the `historical::SessionManager`
+      trait in the `ah-client` pallet with missing implementations of the new_session_genesis method in two different places:
+      - In the pallet_session::SessionManager<T::AccountId> implementation
+      - In the historical::SessionManager<T::AccountId, sp_staking::Exposure<T::AccountId, BalanceOf<T>>>
+      implementation
+
+      Note: the SessionManager trait requires the implementation of new_session_genesis for proper functioning, especially during chain initialization.
+      The pallet-staking-async/ah-client has different operating modes:
+      - Passive: Delegates operations to a fallback implementation
+      - Buffered: Buffers operations for later processing
+      - Active: Performs operations directly
+crates:
+- name: pallet-staking-async-ah-client
+  bump: patch

substrate/frame/staking-async/ah-client/src/lib.rs

@@ -226,7 +226,7 @@ pub mod pallet {
 	use alloc::vec;
 	use frame_support::traits::UnixTime;
 	use frame_system::pallet_prelude::*;
-	use pallet_session::historical;
+	use pallet_session::{historical, SessionManager};
 	use sp_runtime::{Perbill, Saturating};
 	use sp_staking::{
 		offence::{OffenceSeverity, OnOffenceHandler},
@@ -527,8 +527,17 @@ pub mod pallet {
 				.map(|v| v.into_iter().map(|v| (v, sp_staking::Exposure::default())).collect())
 		}
 
-		// We don't implement `new_session_genesis` because we rely on the default implementation
-		// which calls `new_session`
+		fn new_session_genesis(
+			new_index: SessionIndex,
+		) -> Option<Vec<(T::AccountId, sp_staking::Exposure<T::AccountId, BalanceOf<T>>)>> {
+			if Mode::<T>::get() == OperatingMode::Passive {
+				T::Fallback::new_session_genesis(new_index).map(|validators| {
+					validators.into_iter().map(|v| (v, sp_staking::Exposure::default())).collect()
+				})
+			} else {
+				None
+			}
+		}
 
 		fn start_session(start_index: SessionIndex) {
 			<Self as pallet_session::SessionManager<_>>::start_session(start_index)
@@ -555,6 +564,14 @@ pub mod pallet {
 			}
 		}
 
+		fn new_session_genesis(new_index: SessionIndex) -> Option<Vec<T::AccountId>> {
+			if Mode::<T>::get() == OperatingMode::Passive {
+				T::Fallback::new_session_genesis(new_index)
+			} else {
+				None
+			}
+		}
+
 		fn end_session(session_index: u32) {
 			match Mode::<T>::get() {
 				OperatingMode::Passive => T::Fallback::end_session(session_index),