Ensure author inherent included (#17)

* Ensure that author inherent is included

* add comment to explain why it's needed

* typo

* apply suggestions

pallets/author-inherent/src/lib.rs

@@ -95,6 +95,10 @@ pub mod pallet {
 	#[pallet::storage]
 	pub type Author<T: Config> = StorageValue<_, T::AuthorId, OptionQuery>;
 
+	/// Check if the inherent was included
+	#[pallet::storage]
+	pub type InherentIncluded<T: Config> = StorageValue<_, bool, ValueQuery>;
+
 	#[pallet::hooks]
 	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
 		fn on_initialize(_: BlockNumberFor<T>) -> Weight {
@@ -106,7 +110,18 @@ pub mod pallet {
 				<Author<T>>::put(&author);
 			}
 
-			T::DbWeight::get().writes(1)
+			// on_initialize: 1 write
+			// on_finalize: 1 read + 1 write
+			T::DbWeight::get().reads_writes(1, 2)
+		}
+		fn on_finalize(_: BlockNumberFor<T>) {
+			// According to parity, the only way to ensure that a mandatory inherent is included
+			// is by checking on block finalization that the inherent set a particular storage item:
+			// https://github.com/paritytech/polkadot-sdk/issues/2841#issuecomment-1876040854
+			assert!(
+				InherentIncluded::<T>::take() == true,
+				"Block invalid, missing inherent `kick_off_authorship_validation`"
+			);
 		}
 	}
 
@@ -130,6 +145,8 @@ pub mod pallet {
 				"Block invalid, supplied author is not eligible."
 			);
 
+			InherentIncluded::<T>::put(true);
+
 			Ok(Pays::No.into())
 		}
 	}

pallets/author-inherent/src/weights.rs

@@ -77,7 +77,7 @@ impl<T: frame_system::Config> WeightInfo for SubstrateWeight<T> {
 		// Minimum execution time: 25_775_000 picoseconds.
 		Weight::from_parts(26_398_000, 10418)
 			.saturating_add(T::DbWeight::get().reads(6_u64))
-			.saturating_add(T::DbWeight::get().writes(1_u64))
+			.saturating_add(T::DbWeight::get().writes(2_u64))
 	}
 }