Finality Verifier Pallet (#629)

* Add skeleton for `pallet-finality-verifier`

* Sketch out implementation for importing finality proofs

* Get pallet compiling

* Introduce skeleton for mock runtime

* Start using real Grandpa types in finality pallet

* Redefine types in header chain primitives crate

* Implement HeaderChain for Substrate bridge pallet

* Plug Substrate Bridge Pallet into verifier mock

* Fix compilation of `header-chain` primitives

* Start writing to base pallet storage

* Add first "cross-pallet" test

* Move keyring primitives used in tests to shared crate

* Stop pulling `std` deps into `no_std` builds

* Revert "Stop pulling `std` deps into `no_std` builds"

This reverts commit f74dd660652f98b7336936d1534a4e63cc9169a5.

* Revert "Move keyring primitives used in tests to shared crate"

This reverts commit b774fa730b2cdc40545afff308a66b0840266001.

* Use new SS58Prefix type in mock

* Start using `bp-test-utils` in finality pallet

* Start using real justification code

* Get a test working with real justification verification

* Add basic tests for invalid proofs

* Get rid of AncestryProof config type

* Add error types to transaction outcome

* Bound number of headers allowed in a single ancestry proof

* Disallow invalid authority sets

* Remove unused items

* Add some documentation

* Get rid of Clippy warnings

* Rename BaseHeaderChain to TransactionVerifier

* Remove unused code

* Make dummy trait implementations more generic

* Fix more Clippy complaints

* Update tests to use fix for duplicate headers

* Fix benchmarking compilation

* Rename TransactionVerifier to InclusionProofVerifier

bridges/modules/substrate/src/lib.rs

@@ -32,6 +32,7 @@
 #![allow(clippy::large_enum_variant)]
 
 use crate::storage::ImportedHeader;
+use bp_header_chain::AuthoritySet;
 use bp_runtime::{BlockNumberOf, Chain, HashOf, HasherOf, HeaderOf};
 use frame_support::{
 	decl_error, decl_module, decl_storage, dispatch::DispatchResult, ensure, traits::Get, weights::DispatchClass,
@@ -43,7 +44,7 @@ use sp_std::{marker::PhantomData, prelude::*};
 use sp_trie::StorageProof;
 
 // Re-export since the node uses these when configuring genesis
-pub use storage::{AuthoritySet, InitializationData, ScheduledChange};
+pub use storage::{InitializationData, ScheduledChange};
 
 pub use storage_proof::StorageProofChecker;
 
@@ -361,6 +362,38 @@ impl<T: Config> Module<T> {
 	}
 }
 
+impl<T: Config> bp_header_chain::HeaderChain<BridgedHeader<T>> for Module<T> {
+	fn best_finalized() -> BridgedHeader<T> {
+		PalletStorage::<T>::new().best_finalized_header().header
+	}
+
+	fn authority_set() -> AuthoritySet {
+		PalletStorage::<T>::new().current_authority_set()
+	}
+
+	fn import_header(header: BridgedHeader<T>) -> Result<(), ()> {
+		let mut verifier = verifier::Verifier {
+			storage: PalletStorage::<T>::new(),
+		};
+
+		let _ = verifier.import_header(header.hash(), header).map_err(|_| ())?;
+
+		Ok(())
+	}
+
+	fn import_finality_proof(header: BridgedHeader<T>, finality_proof: Vec<u8>) -> Result<(), ()> {
+		let mut verifier = verifier::Verifier {
+			storage: PalletStorage::<T>::new(),
+		};
+
+		let _ = verifier
+			.import_finality_proof(header.hash(), finality_proof.into())
+			.map_err(|_| ())?;
+
+		Ok(())
+	}
+}
+
 /// Ensure that the origin is either root, or `ModuleOwner`.
 fn ensure_owner_or_root<T: Config>(origin: T::Origin) -> Result<(), BadOrigin> {
 	match origin.into() {