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/babe/src/lib.rs

@@ -123,7 +123,7 @@ decl_storage! {
 		pub EpochIndex get(epoch_index): u64;
 
 		/// Current epoch authorities.
-		pub Authorities get(authorities) config(): Vec<(AuthorityId, BabeWeight)>;
+		pub Authorities get(authorities): Vec<(AuthorityId, BabeWeight)>;
 
 		/// Slot at which the current epoch started. It is possible that no
 		/// block was authored at the given slot and the epoch change was
@@ -163,6 +163,18 @@ decl_storage! {
 		SegmentIndex build(|_| 0): u32;
 		UnderConstruction: map u32 => Vec<[u8; 32 /* VRF_OUTPUT_LENGTH */]>;
 	}
+	add_extra_genesis {
+		config(authorities): Vec<(AuthorityId, BabeWeight)>;
+		build(|
+			storage: &mut (sr_primitives::StorageOverlay, sr_primitives::ChildrenStorageOverlay),
+			config: &GenesisConfig
+		| {
+			runtime_io::with_storage(
+				storage,
+				|| Module::<T>::initialize_authorities(&config.authorities),
+			);
+		})
+	}
 }
 
 decl_module! {
@@ -292,6 +304,12 @@ impl<T: Trait> Module<T> {
 		this_randomness
 	}
 
+	fn initialize_authorities(authorities: &[(AuthorityId, BabeWeight)]) {
+		if !authorities.is_empty() {
+			assert!(Authorities::get().is_empty(), "Authorities are already initialized!");
+			Authorities::put_ref(authorities);
+		}
+	}
 }
 
 impl<T: Trait> OnTimestampSet<T::Moment> for Module<T> {
@@ -300,6 +318,14 @@ impl<T: Trait> OnTimestampSet<T::Moment> for Module<T> {
 
 impl<T: Trait> session::OneSessionHandler<T::AccountId> for Module<T> {
 	type Key = AuthorityId;
+
+	fn on_genesis_session<'a, I: 'a>(validators: I)
+		where I: Iterator<Item=(&'a T::AccountId, AuthorityId)>
+	{
+		let authorities = validators.map(|(_, k)| (k, 1)).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, AuthorityId)>
 	{