add a current_epoch to BabeApi (#7789)

* add a `current_epoch` to BabeApi

* add current_epoch_start back again

* fix node-runtime

* bump spec version

substrate/primitives/consensus/babe/src/lib.rs

@@ -350,6 +350,21 @@ impl OpaqueKeyOwnershipProof {
 	}
 }
 
+/// BABE epoch information
+#[derive(Decode, Encode, PartialEq, Eq, Clone, Debug)]
+pub struct Epoch {
+	/// The epoch index.
+	pub epoch_index: u64,
+	/// The starting slot of the epoch.
+	pub start_slot: SlotNumber,
+	/// The duration of this epoch.
+	pub duration: SlotNumber,
+	/// The authorities and their weights.
+	pub authorities: Vec<(AuthorityId, BabeAuthorityWeight)>,
+	/// Randomness for this epoch.
+	pub randomness: [u8; VRF_OUTPUT_LENGTH],
+}
+
 sp_api::decl_runtime_apis! {
 	/// API necessary for block authorship with BABE.
 	#[api_version(2)]
@@ -364,6 +379,9 @@ sp_api::decl_runtime_apis! {
 		/// Returns the slot number that started the current epoch.
 		fn current_epoch_start() -> SlotNumber;
 
+		/// Returns information regarding the current epoch.
+		fn current_epoch() -> Epoch;
+
 		/// Generates a proof of key ownership for the given authority in the
 		/// current epoch. An example usage of this module is coupled with the
 		/// session historical module to prove that a given authority key is