Offences reporting and slashing

core/sr-staking-primitives/src/offence.rs

@@ -38,12 +38,6 @@ pub type Kind = [u8; 16];
 /// so that we can slash it accordingly.
 pub type OffenceCount = u32;
 
-/// A type that represents a point in time on an abstract timescale.
-///
-/// See `Offence::time_slot` for details. The only requirement is that such timescale could be
-/// represented by a single `u128` value.
-pub type TimeSlot = u128;
-
 /// A trait implemented by an offence report.
 ///
 /// This trait assumes that the offence is legitimate and was validated already.
@@ -53,13 +47,21 @@ pub trait Offence<Offender> {
 	/// Identifier which is unique for this kind of an offence.
 	const ID: Kind;
 
+	/// A type that represents a point in time on an abstract timescale.
+	///
+	/// See `Offence::time_slot` for details. The only requirement is that such timescale could be
+	/// represented by a single `u128` value.
+	type TimeSlot: Clone + codec::Codec + Ord;
+
 	/// The list of all offenders involved in this incident.
 	///
 	/// The list has no duplicates, so it is rather a set.
 	fn offenders(&self) -> Vec<Offender>;
 
 	/// The session index that is used for querying the validator set for the `slash_fraction`
 	/// function.
+	///
+	/// This is used for filtering historical sessions.
 	fn session_index(&self) -> SessionIndex;
 
 	/// Return a validator set count at the time when the offence took place.
@@ -76,7 +78,7 @@ pub trait Offence<Offender> {
 	///
 	/// As an example, for GRANDPA timescale could be a round number and for BABE it could be a slot
 	/// number. Note that for GRANDPA the round number is reset each epoch.
-	fn time_slot(&self) -> TimeSlot;
+	fn time_slot(&self) -> Self::TimeSlot;
 
 	/// A slash fraction of the total exposure that should be slashed for this
 	/// particular offence kind for the given parameters that happened at a singular `TimeSlot`.

srml/babe/src/lib.rs

@@ -31,7 +31,7 @@ use sr_primitives::{generic::DigestItem, ConsensusEngineId, Perbill};
 use sr_primitives::traits::{IsMember, SaturatedConversion, Saturating, RandomnessBeacon, Convert};
 use sr_staking_primitives::{
 	SessionIndex,
-	offence::{Offence, TimeSlot, Kind},
+	offence::{Offence, Kind},
 };
 #[cfg(feature = "std")]
 use timestamp::TimestampInherentData;
@@ -266,6 +266,7 @@ struct BabeEquivocationOffence<FullIdentification> {
 
 impl<FullIdentification: Clone> Offence<FullIdentification> for BabeEquivocationOffence<FullIdentification> {
 	const ID: Kind = *b"babe:equivocatio";
+	type TimeSlot = u64;
 
 	fn offenders(&self) -> Vec<FullIdentification> {
 		vec![self.offender.clone()]
@@ -279,8 +280,8 @@ impl<FullIdentification: Clone> Offence<FullIdentification> for BabeEquivocation
 		self.validator_set_count
 	}
 
-	fn time_slot(&self) -> TimeSlot {
-		self.slot as TimeSlot
+	fn time_slot(&self) -> u64 {
+		self.slot
 	}
 
 	fn slash_fraction(

srml/grandpa/src/lib.rs

@@ -41,7 +41,7 @@ use sr_primitives::{
 };
 use sr_staking_primitives::{
 	SessionIndex,
-	offence::{TimeSlot, Offence, Kind},
+	offence::{Offence, Kind},
 };
 use fg_primitives::{ScheduledChange, ConsensusLog, GRANDPA_ENGINE_ID};
 pub use fg_primitives::{AuthorityId, AuthorityWeight};
@@ -382,12 +382,20 @@ impl<T: Trait> finality_tracker::OnFinalizationStalled<T::BlockNumber> for Modul
 	}
 }
 
+/// A round number and set id which point on the time of an offence.
+#[derive(Copy, Clone, PartialOrd, Ord, Eq, PartialEq, Encode, Decode)]
+struct GrandpaTimeSlot {
+	// The order of these matters for `derive(Ord)`.
+	set_id: u64,
+	round: u64,
+}
+
 // TODO [slashing]: Integrate this.
 /// A grandpa equivocation offence report.
 #[allow(dead_code)]
 struct GrandpaEquivocationOffence<FullIdentification> {
-	/// A round in which the incident happened.
-	round: u64,
+	/// Time slot at which this incident happened.
+	time_slot: GrandpaTimeSlot,
 	/// The session index in which the incident happened.
 	session_index: SessionIndex,
 	/// The size of the validator set at the time of the offence.
@@ -398,6 +406,7 @@ struct GrandpaEquivocationOffence<FullIdentification> {
 
 impl<FullIdentification: Clone> Offence<FullIdentification> for GrandpaEquivocationOffence<FullIdentification> {
 	const ID: Kind = *b"grandpa:equivoca";
+	type TimeSlot = GrandpaTimeSlot;
 
 	fn offenders(&self) -> Vec<FullIdentification> {
 		vec![self.offender.clone()]
@@ -411,8 +420,8 @@ impl<FullIdentification: Clone> Offence<FullIdentification> for GrandpaEquivocat
 		self.validator_set_count
 	}
 
-	fn time_slot(&self) -> TimeSlot {
-		self.round as TimeSlot
+	fn time_slot(&self) -> GrandpaTimeSlot {
+		self.time_slot
 	}
 
 	fn slash_fraction(

srml/grandpa/src/tests.rs

@@ -282,3 +282,31 @@ fn schedule_resume_only_when_paused() {
 		);
 	});
 }
+
+#[test]
+fn time_slot_have_sane_ord() {
+	// Ensure that `Ord` implementation is sane.
+	const FIXTURE: &[GrandpaTimeSlot] = &[
+		GrandpaTimeSlot {
+			set_id: 0,
+			round: 0,
+		},
+		GrandpaTimeSlot {
+			set_id: 0,
+			round: 1,
+		},
+		GrandpaTimeSlot {
+			set_id: 1,
+			round: 0,
+		},
+		GrandpaTimeSlot {
+			set_id: 1,
+			round: 1,
+		},
+		GrandpaTimeSlot {
+			set_id: 1,
+			round: 2,
+		}
+	];
+	assert!(FIXTURE.windows(2).all(|f| f[0] < f[1]));
+}

srml/im-online/src/lib.rs

@@ -80,7 +80,7 @@ use sr_primitives::{
 };
 use sr_staking_primitives::{
 	SessionIndex, CurrentElectedSet,
-	offence::{ReportOffence, Offence, TimeSlot, Kind},
+	offence::{ReportOffence, Offence, Kind},
 };
 use srml_support::{
 	StorageValue, decl_module, decl_event, decl_storage, StorageDoubleMap, print,
@@ -493,6 +493,7 @@ pub struct UnresponsivenessOffence<Offender> {
 
 impl<Offender: Clone> Offence<Offender> for UnresponsivenessOffence<Offender> {
 	const ID: Kind = *b"im-online:offlin";
+	type TimeSlot = SessionIndex;
 
 	fn offenders(&self) -> Vec<Offender> {
 		self.offenders.clone()
@@ -506,8 +507,8 @@ impl<Offender: Clone> Offence<Offender> for UnresponsivenessOffence<Offender> {
 		self.validator_set_count
 	}
 
-	fn time_slot(&self) -> TimeSlot {
-		self.session_index as TimeSlot
+	fn time_slot(&self) -> SessionIndex {
+		self.session_index as SessionIndex
 	}
 
 	fn slash_fraction(offenders: u32, validator_set_count: u32) -> Perbill {