Expose MMR root through runtime API - use it in BEEFY client (#11183)

* beefy-gadget: allow custom runtime api provider

* beefy-gadget: use mock runtime api in tests

* pallet-mmr: expose mmr root from state through runtime API

* beefy-gadget: get mmr root from runtime state

* pallet-beefy-mmr: remove MmrRoot from header digests

* frame/mmr: move mmr primitives out of frame

* frame/mmr: completely move primitives out of frame

* address review comments

* beefy-mmr: bring back mmr root from header digest

* clippy fixes for rustc 1.60

* address review comments

substrate/frame/merkle-mountain-range/src/lib.rs

@@ -58,7 +58,7 @@
 
 use codec::Encode;
 use frame_support::weights::Weight;
-use sp_runtime::traits;
+use sp_runtime::traits::{self, One, Saturating};
 
 #[cfg(any(feature = "runtime-benchmarks", test))]
 mod benchmarking;
@@ -70,7 +70,30 @@ mod mock;
 mod tests;
 
 pub use pallet::*;
-pub use pallet_mmr_primitives::{self as primitives, NodeIndex};
+pub use sp_mmr_primitives::{self as primitives, Error, LeafDataProvider, LeafIndex, NodeIndex};
+
+/// The most common use case for MMRs is to store historical block hashes,
+/// so that any point in time in the future we can receive a proof about some past
+/// blocks without using excessive on-chain storage.
+///
+/// Hence we implement the [LeafDataProvider] for [ParentNumberAndHash] which is a
+/// crate-local wrapper over [frame_system::Pallet]. Since the current block hash
+/// is not available (since the block is not finished yet),
+/// we use the `parent_hash` here along with parent block number.
+pub struct ParentNumberAndHash<T: frame_system::Config> {
+	_phanthom: sp_std::marker::PhantomData<T>,
+}
+
+impl<T: frame_system::Config> LeafDataProvider for ParentNumberAndHash<T> {
+	type LeafData = (<T as frame_system::Config>::BlockNumber, <T as frame_system::Config>::Hash);
+
+	fn leaf_data() -> Self::LeafData {
+		(
+			frame_system::Pallet::<T>::block_number().saturating_sub(One::one()),
+			frame_system::Pallet::<T>::parent_hash(),
+		)
+	}
+}
 
 pub trait WeightInfo {
 	fn on_initialize(peaks: NodeIndex) -> Weight;
@@ -161,7 +184,7 @@ pub mod pallet {
 	/// Current size of the MMR (number of leaves).
 	#[pallet::storage]
 	#[pallet::getter(fn mmr_leaves)]
-	pub type NumberOfLeaves<T, I = ()> = StorageValue<_, NodeIndex, ValueQuery>;
+	pub type NumberOfLeaves<T, I = ()> = StorageValue<_, LeafIndex, ValueQuery>;
 
 	/// Hashes of the nodes in the MMR.
 	///
@@ -240,7 +263,7 @@ impl<T: Config<I>, I: 'static> Pallet<T, I> {
 	/// all the leaves to be present.
 	/// It may return an error or panic if used incorrectly.
 	pub fn generate_proof(
-		leaf_index: NodeIndex,
+		leaf_index: LeafIndex,
 	) -> Result<(LeafOf<T, I>, primitives::Proof<<T as Config<I>>::Hash>), primitives::Error> {
 		let mmr: ModuleMmr<mmr::storage::OffchainStorage, T, I> = mmr::Mmr::new(Self::mmr_leaves());
 		mmr.generate_proof(leaf_index)
@@ -272,4 +295,9 @@ impl<T: Config<I>, I: 'static> Pallet<T, I> {
 			Err(primitives::Error::Verify.log_debug("The proof is incorrect."))
 		}
 	}
+
+	/// Return the on-chain MMR root hash.
+	pub fn mmr_root() -> <T as Config<I>>::Hash {
+		Self::mmr_root_hash()
+	}
 }

substrate/frame/merkle-mountain-range/src/mmr/mod.rs

@@ -19,7 +19,7 @@ mod mmr;
 pub mod storage;
 pub mod utils;
 
-use crate::primitives::FullLeaf;
+use sp_mmr_primitives::{DataOrHash, FullLeaf};
 use sp_runtime::traits;
 
 pub use self::mmr::{verify_leaf_proof, Mmr};
@@ -28,7 +28,7 @@ pub use self::mmr::{verify_leaf_proof, Mmr};
 pub type NodeOf<T, I, L> = Node<<T as crate::Config<I>>::Hashing, L>;
 
 /// A node stored in the MMR.
-pub type Node<H, L> = crate::primitives::DataOrHash<H, L>;
+pub type Node<H, L> = DataOrHash<H, L>;
 
 /// Default Merging & Hashing behavior for MMR.
 pub struct Hasher<H, L>(sp_std::marker::PhantomData<(H, L)>);

substrate/frame/merkle-mountain-range/src/mock.rs

@@ -20,8 +20,8 @@ use crate::*;
 
 use codec::{Decode, Encode};
 use frame_support::traits::{ConstU32, ConstU64};
-use pallet_mmr_primitives::{Compact, LeafDataProvider};
 use sp_core::H256;
+use sp_mmr_primitives::{Compact, LeafDataProvider};
 use sp_runtime::{
 	testing::Header,
 	traits::{BlakeTwo256, IdentityLookup, Keccak256},
@@ -74,7 +74,7 @@ impl Config for Test {
 
 	type Hashing = Keccak256;
 	type Hash = H256;
-	type LeafData = Compact<Keccak256, (frame_system::Pallet<Test>, LeafData)>;
+	type LeafData = Compact<Keccak256, (ParentNumberAndHash<Test>, LeafData)>;
 	type OnNewRoot = ();
 	type WeightInfo = ();
 }

substrate/frame/merkle-mountain-range/src/tests.rs

@@ -19,11 +19,11 @@ use crate::{mmr::utils, mock::*, *};
 
 use frame_support::traits::OnInitialize;
 use mmr_lib::helper;
-use pallet_mmr_primitives::{Compact, Proof};
 use sp_core::{
 	offchain::{testing::TestOffchainExt, OffchainDbExt, OffchainWorkerExt},
 	H256,
 };
+use sp_mmr_primitives::{Compact, Proof};
 
 pub(crate) fn new_test_ext() -> sp_io::TestExternalities {
 	frame_system::GenesisConfig::default().build_storage::<Test>().unwrap().into()