Support custom fork choice rule (#1339)

* Support custom fork choice rule

* Remove unneeded reexport

* Fix network compile

substrate/core/consensus/aura/src/lib.rs

@@ -61,7 +61,7 @@ use std::sync::Arc;
 use std::time::Duration;
 
 use codec::Encode;
-use consensus_common::{Authorities, BlockImport, Environment, Error as ConsensusError, Proposer};
+use consensus_common::{Authorities, BlockImport, Environment, Error as ConsensusError, Proposer, ForkChoiceStrategy};
 use consensus_common::import_queue::{Verifier, BasicQueue};
 use client::ChainHead;
 use client::block_builder::api::BlockBuilder as BlockBuilderApi;
@@ -324,6 +324,7 @@ pub fn start_aura<B, C, E, I, SO, Error>(
 							body: Some(body),
 							finalized: false,
 							auxiliary: Vec::new(),
+							fork_choice: ForkChoiceStrategy::LongestChain,
 						};
 
 						if let Err(e) = block_import.import_block(import_block, None) {
@@ -524,6 +525,7 @@ impl<B: Block, C, E, MakeInherent, Inherent> Verifier<B> for AuraVerifier<C, E,
 					finalized: false,
 					justification,
 					auxiliary: Vec::new(),
+					fork_choice: ForkChoiceStrategy::LongestChain,
 				};
 
 				// FIXME: extract authorities - https://github.com/paritytech/substrate/issues/1019

substrate/core/consensus/common/src/block_import.rs

@@ -53,6 +53,15 @@ pub enum BlockOrigin {
 	File,
 }
 
+/// Fork choice strategy.
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum ForkChoiceStrategy {
+	/// Longest chain fork choice.
+	LongestChain,
+	/// Custom fork choice rule, where true indicates the new block should be the best block.
+	Custom(bool),
+}
+
 /// Data required to import a Block
 pub struct ImportBlock<Block: BlockT> {
 	/// Origin of the Block
@@ -83,6 +92,8 @@ pub struct ImportBlock<Block: BlockT> {
 	/// Contains a list of key-value pairs. If values are `None`, the keys
 	/// will be deleted.
 	pub auxiliary: Vec<(Vec<u8>, Option<Vec<u8>>)>,
+	/// Fork choice strategy of this import.
+	pub fork_choice: ForkChoiceStrategy,
 }
 
 impl<Block: BlockT> ImportBlock<Block> {

substrate/core/consensus/common/src/lib.rs

@@ -55,7 +55,7 @@ pub mod evaluation;
 const MAX_TRANSACTIONS_SIZE: usize = 4 * 1024 * 1024;
 
 pub use self::error::{Error, ErrorKind};
-pub use block_import::{BlockImport, ImportBlock, BlockOrigin, ImportResult};
+pub use block_import::{BlockImport, ImportBlock, BlockOrigin, ImportResult, ForkChoiceStrategy};
 
 /// Trait for getting the authorities at a given block.
 pub trait Authorities<B: Block> {