beacon, yamltests: process slashings and pass the test

beacon/src/executive/transition/per_epoch/mod.rs

@@ -3,3 +3,4 @@ mod justification;
 mod crosslink;
 mod reward;
 mod registry;
+mod slashing;

beacon/src/executive/transition/per_epoch/slashing.rs

+use crate::{Config, BeaconState};
+use core::cmp::min;
+
+impl<C: Config> BeaconState<C> {
+	/// Process slashings
+	pub fn process_slashings(&mut self) {
+		let current_epoch = self.current_epoch();
+		let total_balance = self.total_active_balance();
+
+		for index in 0..(self.validators.len() as u64) {
+			let penalty = {
+				let validator = &self.validators[index as usize];
+				if validator.slashed &&
+					current_epoch + C::epochs_per_slashings_vector() / 2 ==
+					validator.withdrawable_epoch
+				{
+					let increment = C::effective_balance_increment();
+					let penalty_numerator = validator.effective_balance / increment *
+						min(self.slashings.iter().fold(0, |acc, x| acc + *x) * 3, total_balance);
+					let penalty = penalty_numerator / total_balance * increment;
+
+					Some(penalty)
+				} else {
+					None
+				}
+			};
+			if let Some(penalty) = penalty {
+				self.decrease_balance(index, penalty);
+			}
+		}
+	}
+}

yamltests/transitiontests/src/epoch_processing.rs

@@ -49,3 +49,19 @@ impl<C: Config> Test for RegistryUpdatesTest<C> {
 		});
 	}
 }
+
+#[derive(Serialize, Deserialize, Debug)]
+#[serde(deny_unknown_fields)]
+pub struct SlashingsTest<C: Config> {
+	pub description: String,
+	pub pre: BeaconState<C>,
+	pub post: Option<BeaconState<C>>,
+}
+
+impl<C: Config> Test for SlashingsTest<C> {
+	fn run(&self) {
+		run_test_with(&self.description, &self.pre, self.post.as_ref(), |state| {
+			Ok(state.process_slashings())
+		});
+	}
+}

yamltests/transitiontests/src/main.rs

@@ -48,6 +48,7 @@ fn run_all<C: Config + serde::Serialize + DeserializeOwned>(runner: &str, file:
 		"justification_and_finalization" => run::<JustificationAndFinalizationTest<C>>(file),
 		"crosslinks" => run::<CrosslinksTest<C>>(file),
 		"registry_updates" => run::<RegistryUpdatesTest<C>>(file),
+		"slashings" => run::<SlashingsTest<C>>(file),
 		// "blocks" => run::<BlocksTest, _>(file, &config),
 		// "slots" => run::<SlotsTest, _>(file, &config),
 		_ => panic!("Unsupported runner"),