Adds support for returning a custom header from validate_block (#825)

* Adds support for returning a custom header from `validate_block`

This adds support for returning a custom header from `validate_block`. Before this, we always
returned the header of the block that was validated (and still do it by default). However, after
this pr it is possible to set a custom header or better custom head data that will be returned
instead from `validate_block`. This can be for example when a chain wants to fork.

* FMT

test/runtime/src/lib.rs

@@ -27,6 +27,8 @@ pub mod wasm_spec_version_incremented {
 	include!(concat!(env!("OUT_DIR"), "/wasm_binary_spec_version_incremented.rs"));
 }
 
+mod test_pallet;
+
 use frame_support::traits::OnRuntimeUpgrade;
 use sp_api::{decl_runtime_apis, impl_runtime_apis};
 use sp_core::OpaqueMetadata;
@@ -58,6 +60,7 @@ pub use pallet_timestamp::Call as TimestampCall;
 #[cfg(any(feature = "std", test))]
 pub use sp_runtime::BuildStorage;
 pub use sp_runtime::{Perbill, Permill};
+pub use test_pallet::Call as TestPalletCall;
 
 pub type SessionHandlers = ();
 
@@ -265,20 +268,21 @@ parameter_types! {
 	pub storage ParachainId: cumulus_primitives_core::ParaId = 100.into();
 }
 
+impl test_pallet::Config for Runtime {}
+
 construct_runtime! {
 	pub enum Runtime where
 		Block = Block,
 		NodeBlock = NodeBlock,
 		UncheckedExtrinsic = UncheckedExtrinsic,
 	{
-		System: frame_system::{Pallet, Call, Storage, Config, Event<T>},
-		ParachainSystem: cumulus_pallet_parachain_system::{
-			Pallet, Call, Config, Storage, Inherent, Event<T>, ValidateUnsigned,
-		},
-		Timestamp: pallet_timestamp::{Pallet, Call, Storage, Inherent},
-		Balances: pallet_balances::{Pallet, Call, Storage, Config<T>, Event<T>},
-		Sudo: pallet_sudo::{Pallet, Call, Storage, Config<T>, Event<T>},
-		TransactionPayment: pallet_transaction_payment::{Pallet, Storage},
+		System: frame_system,
+		ParachainSystem: cumulus_pallet_parachain_system,
+		Timestamp: pallet_timestamp,
+		Balances: pallet_balances,
+		Sudo: pallet_sudo,
+		TransactionPayment: pallet_transaction_payment,
+		TestPallet: test_pallet,
 	}
 }
 

test/runtime/src/test_pallet.rs

@@ -0,0 +1,49 @@
+// Copyright 2021 Parity Technologies (UK) Ltd.
+// This file is part of Cumulus.
+
+// Cumulus is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Cumulus is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Cumulus.  If not, see <http://www.gnu.org/licenses/>.
+
+/// A special pallet that exposes dispatchables that are only useful for testing.
+pub use pallet::*;
+
+#[frame_support::pallet]
+pub mod pallet {
+	use frame_support::pallet_prelude::*;
+	use frame_system::pallet_prelude::*;
+
+	#[pallet::pallet]
+	#[pallet::generate_store(pub(super) trait Store)]
+	pub struct Pallet<T>(_);
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config + cumulus_pallet_parachain_system::Config {}
+
+	#[pallet::hooks]
+	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {}
+
+	#[pallet::call]
+	impl<T: Config> Pallet<T> {
+		/// A test dispatchable for setting a custom head data in `validate_block`.
+		#[pallet::weight(0)]
+		pub fn set_custom_validation_head_data(
+			_: OriginFor<T>,
+			custom_header: sp_std::vec::Vec<u8>,
+		) -> DispatchResult {
+			cumulus_pallet_parachain_system::Pallet::<T>::set_custom_validation_head_data(
+				custom_header,
+			);
+			Ok(())
+		}
+	}
+}