no default uncles

ethcore/res/ethereum/kovan.json

@@ -23,7 +23,8 @@
 					]
 				},
 				"validateScoreTransition": 1000000,
-				"validateStepTransition": 1500000
+				"validateStepTransition": 1500000,
+				"maximumUncleCount": 2
 			}
 		}
 	},

ethcore/src/engines/authority_round/mod.rs

@@ -65,6 +65,8 @@ pub struct AuthorityRoundParams {
 	pub immediate_transitions: bool,
 	/// Block reward in base units.
 	pub block_reward: U256,
+	/// Number of accepted uncles.
+	pub maximum_uncle_count: usize,
 }
 
 impl From<ethjson::spec::AuthorityRoundParams> for AuthorityRoundParams {
@@ -77,6 +79,7 @@ impl From<ethjson::spec::AuthorityRoundParams> for AuthorityRoundParams {
 			validate_step_transition: p.validate_step_transition.map_or(0, Into::into),
 			immediate_transitions: p.immediate_transitions.unwrap_or(false),
 			block_reward: p.block_reward.map_or_else(Default::default, Into::into),
+			maximum_uncle_count: p.maximum_uncle_count.map_or(0, Into::into),
 		}
 	}
 }
@@ -218,6 +221,7 @@ pub struct AuthorityRound {
 	epoch_manager: Mutex<EpochManager>,
 	immediate_transitions: bool,
 	block_reward: U256,
+	maximum_uncle_count: usize,
 	machine: EthereumMachine,
 }
 
@@ -365,6 +369,7 @@ impl AuthorityRound {
 				epoch_manager: Mutex::new(EpochManager::blank()),
 				immediate_transitions: our_params.immediate_transitions,
 				block_reward: our_params.block_reward,
+				maximum_uncle_count: our_params.maximum_uncle_count,
 				machine: machine,
 			});
 
@@ -436,6 +441,8 @@ impl Engine<EthereumMachine> for AuthorityRound {
 		]
 	}
 
+	fn maximum_uncle_count(&self) -> usize { self.maximum_uncle_count }
+
 	fn populate_from_parent(&self, header: &mut Header, parent: &Header) {
 		// Chain scoring: total weight is sqrt(U256::max_value())*height - step
 		let new_difficulty = U256::from(U128::max_value()) + header_step(parent).expect("Header has been verified; qed").into() - self.step.load().into();
@@ -949,6 +956,7 @@ mod tests {
 			validate_score_transition: 0,
 			validate_step_transition: 0,
 			immediate_transitions: true,
+			maximum_uncle_count: 0,
 			block_reward: Default::default(),
 		};
 

ethcore/src/engines/mod.rs

@@ -192,7 +192,7 @@ pub trait Engine<M: Machine>: Sync + Send {
 	fn extra_info(&self, _header: &M::Header) -> BTreeMap<String, String> { BTreeMap::new() }
 
 	/// Maximum number of uncles a block is allowed to declare.
-	fn maximum_uncle_count(&self) -> usize { 2 }
+	fn maximum_uncle_count(&self) -> usize { 0 }
 	/// The number of generations back that uncles can be.
 	fn maximum_uncle_age(&self) -> usize { 6 }
 

ethcore/src/ethereum/ethash.rs

@@ -181,6 +181,8 @@ impl Engine<EthereumMachine> for Arc<Ethash> {
 		}
 	}
 
+	fn maximum_uncle_count(&self) -> usize { 2 }
+
 	fn populate_from_parent(&self, header: &mut Header, parent: &Header) {
 		let difficulty = self.calculate_difficulty(header, parent);
 		header.set_difficulty(difficulty);

json/src/spec/authority_round.rs

@@ -43,6 +43,8 @@ pub struct AuthorityRoundParams {
 	/// Reward per block in wei.
 	#[serde(rename="blockReward")]
 	pub block_reward: Option<Uint>,
+	#[serde(rename="maximumUncleCount")]
+	pub maximum_uncle_count: Option<Uint>,
 }
 
 /// Authority engine deserialization.