From 7784bdeffed5090637f90dc91c8f86023508f945 Mon Sep 17 00:00:00 2001
From: Wei Tang <hi@that.world>
Date: Tue, 28 Apr 2020 12:50:40 +0200
Subject: [PATCH] Versioned NextConfigDescriptor for BABE (#5789)

---
 substrate/client/consensus/babe/src/lib.rs    |  2 +-
 .../primitives/consensus/babe/src/digests.rs  | 23 +++++++++++++++++--
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/substrate/client/consensus/babe/src/lib.rs b/substrate/client/consensus/babe/src/lib.rs
index e314e7a43c..028fe8e5e3 100644
--- a/substrate/client/consensus/babe/src/lib.rs
+++ b/substrate/client/consensus/babe/src/lib.rs
@@ -1065,7 +1065,7 @@ impl<Block, Client, Inner> BlockImport<Block> for BabeBlockImport<Block, Client,
 				ConsensusError::ClientImport(Error::<Block>::FetchEpoch(parent_hash).into())
 			})?;
 
-			let epoch_config = next_config_digest.unwrap_or_else(
+			let epoch_config = next_config_digest.map(Into::into).unwrap_or_else(
 				|| viable_epoch.as_ref().config.clone()
 			);
 
diff --git a/substrate/primitives/consensus/babe/src/digests.rs b/substrate/primitives/consensus/babe/src/digests.rs
index f113912d83..141d6cf4bd 100644
--- a/substrate/primitives/consensus/babe/src/digests.rs
+++ b/substrate/primitives/consensus/babe/src/digests.rs
@@ -18,7 +18,7 @@
 
 #[cfg(feature = "std")]
 use super::{BABE_ENGINE_ID, AuthoritySignature};
-use super::{AuthorityId, AuthorityIndex, SlotNumber, BabeAuthorityWeight, BabeEpochConfiguration};
+use super::{AuthorityId, AuthorityIndex, SlotNumber, BabeAuthorityWeight, BabeEpochConfiguration, AllowedSlots};
 #[cfg(feature = "std")]
 use sp_runtime::{DigestItem, generic::OpaqueDigestItemId};
 #[cfg(feature = "std")]
@@ -183,7 +183,26 @@ pub struct NextEpochDescriptor {
 
 /// Information about the next epoch config, if changed. This is broadcast in the first
 /// block of the epoch, and applies using the same rules as `NextEpochDescriptor`.
-pub type NextConfigDescriptor = BabeEpochConfiguration;
+#[derive(Decode, Encode, PartialEq, Eq, Clone, RuntimeDebug)]
+pub enum NextConfigDescriptor {
+	/// Version 1.
+	#[codec(index = "1")]
+	V1 {
+		/// Value of `c` in `BabeEpochConfiguration`.
+		c: (u64, u64),
+		/// Value of `allowed_slots` in `BabeEpochConfiguration`.
+		allowed_slots: AllowedSlots,
+	}
+}
+
+impl From<NextConfigDescriptor> for BabeEpochConfiguration {
+	fn from(desc: NextConfigDescriptor) -> Self {
+		match desc {
+			NextConfigDescriptor::V1 { c, allowed_slots } =>
+				Self { c, allowed_slots },
+		}
+	}
+}
 
 /// A digest item which is usable with BABE consensus.
 #[cfg(feature = "std")]