session: add handler for genesis session (#3413)

* session: add handler for genesis session

* node: bump spec version

* aura: handle on_genesis_session

* srml: make sure we don't re-initialize genesis authorities

* session: fix mock

* node: remove genesis authorities from chain spec

* staking: fix mock

* srml: don't initialize genesis authorities twice

* aura: don't reinitialize genesis authorities

* aura: fix runtime_io dependency

* Bump runtime

substrate/srml/aura/src/lib.rs

@@ -165,7 +165,19 @@ decl_storage! {
 		LastTimestamp get(last) build(|_| 0.into()): T::Moment;
 
 		/// The current authorities
-		pub Authorities get(authorities) config(): Vec<T::AuthorityId>;
+		pub Authorities get(authorities): Vec<T::AuthorityId>;
+	}
+	add_extra_genesis {
+		config(authorities): Vec<T::AuthorityId>;
+		build(|
+			storage: &mut (sr_primitives::StorageOverlay, sr_primitives::ChildrenStorageOverlay),
+			config: &GenesisConfig<T>
+		| {
+			runtime_io::with_storage(
+				storage,
+				|| Module::<T>::initialize_authorities(&config.authorities),
+			);
+		})
 	}
 }
 
@@ -183,11 +195,25 @@ impl<T: Trait> Module<T> {
 		);
 		<system::Module<T>>::deposit_log(log.into());
 	}
+
+	fn initialize_authorities(authorities: &[T::AuthorityId]) {
+		if !authorities.is_empty() {
+			assert!(<Authorities<T>>::get().is_empty(), "Authorities are already initialized!");
+			<Authorities<T>>::put_ref(authorities);
+		}
+	}
 }
 
 impl<T: Trait> session::OneSessionHandler<T::AccountId> for Module<T> {
 	type Key = T::AuthorityId;
 
+	fn on_genesis_session<'a, I: 'a>(validators: I)
+		where I: Iterator<Item=(&'a T::AccountId, T::AuthorityId)>
+	{
+		let authorities = validators.map(|(_, k)| k).collect::<Vec<_>>();
+		Self::initialize_authorities(&authorities);
+	}
+
 	fn on_new_session<'a, I: 'a>(changed: bool, validators: I, _queued_validators: I)
 		where I: Iterator<Item=(&'a T::AccountId, T::AuthorityId)>
 	{
@@ -200,6 +226,7 @@ impl<T: Trait> session::OneSessionHandler<T::AccountId> for Module<T> {
 			}
 		}
 	}
+
 	fn on_disabled(i: usize) {
 		let log: DigestItem<T::Hash> = DigestItem::Consensus(
 			AURA_ENGINE_ID,