GRANDPA finality proof draft

core/client/src/genesis.rs

@@ -70,7 +70,7 @@ mod tests {
 			let signature = Pair::from(Keyring::from_public(Public::from_raw(tx.from.to_fixed_bytes())).unwrap())
 				.sign(&tx.encode()).into();
 
-			Extrinsic { transfer: tx, signature }
+			Extrinsic::Transfer(tx, signature)
 		}).collect::<Vec<_>>();
 
 		let extrinsics_root = ordered_trie_root::<Blake2Hasher, _, _>(transactions.iter().map(Encode::encode)).into();

core/finality-grandpa/primitives/src/lib.rs

@@ -97,6 +97,10 @@ decl_runtime_apis! {
 
 		/// Get the current GRANDPA authorities and weights. This should not change except
 		/// for when changes are scheduled and the corresponding delay has passed.
+		///
+		/// When called at block B, it will return the set of authorities that should be
+		/// used to finalize descendants of this block (B+1, B+2, ...). The block B itself
+		/// is finalized by the authorities from block B-1.
 		fn grandpa_authorities() -> Vec<(Ed25519AuthorityId, u64)>;
 	}
 }