Introduce a Slot type (#7997)

* Introduce a `Slot` type

Instead of having some type definition that only was used in half of the
code or directly using `u64`, this adds a new unit type wrapper `Slot`.
This makes it especially easy for the outside api to know what type is
expected/returned.

* Change epoch duratioC

* rename all instances of slot number to slot

* Make the constructor private

Co-authored-by: André Silva <andrerfosilva@gmail.com>

substrate/primitives/consensus/aura/Cargo.toml

@@ -20,6 +20,7 @@ sp-api = { version = "2.0.0", default-features = false, path = "../../api" }
 sp-runtime = { version = "2.0.0", default-features = false, path = "../../runtime" }
 sp-inherents = { version = "2.0.0", default-features = false, path = "../../inherents" }
 sp-timestamp = { version = "2.0.0", default-features = false, path = "../../timestamp" }
+sp-consensus-slots = { version = "0.8.1", default-features = false, path = "../slots" }
 
 [features]
 default = ["std"]

substrate/primitives/consensus/aura/src/inherents.rs

@@ -26,7 +26,7 @@ use sp_inherents::{InherentDataProviders, ProvideInherentData};
 pub const INHERENT_IDENTIFIER: InherentIdentifier = *b"auraslot";
 
 /// The type of the Aura inherent.
-pub type InherentType = u64;
+pub type InherentType = sp_consensus_slots::Slot;
 
 /// Auxiliary trait to extract Aura inherent data.
 pub trait AuraInherentData {
@@ -87,8 +87,8 @@ impl ProvideInherentData for InherentDataProvider {
 		use sp_timestamp::TimestampInherentData;
 
 		let timestamp = inherent_data.timestamp_inherent_data()?;
-		let slot_num = timestamp / self.slot_duration;
-		inherent_data.put_data(INHERENT_IDENTIFIER, &slot_num)
+		let slot = timestamp / self.slot_duration;
+		inherent_data.put_data(INHERENT_IDENTIFIER, &slot)
 	}
 
 	fn error_to_string(&self, error: &[u8]) -> Option<String> {

substrate/primitives/consensus/babe/src/digests.rs

@@ -19,7 +19,7 @@
 
 use super::{
 	AllowedSlots, AuthorityId, AuthorityIndex, AuthoritySignature, BabeAuthorityWeight,
-	BabeEpochConfiguration, SlotNumber, BABE_ENGINE_ID,
+	BabeEpochConfiguration, Slot, BABE_ENGINE_ID,
 };
 use codec::{Codec, Decode, Encode};
 use sp_std::vec::Vec;
@@ -32,8 +32,8 @@ use sp_consensus_vrf::schnorrkel::{Randomness, VRFOutput, VRFProof};
 pub struct PrimaryPreDigest {
 	/// Authority index
 	pub authority_index: super::AuthorityIndex,
-	/// Slot number
-	pub slot_number: SlotNumber,
+	/// Slot
+	pub slot: Slot,
 	/// VRF output
 	pub vrf_output: VRFOutput,
 	/// VRF proof
@@ -50,8 +50,8 @@ pub struct SecondaryPlainPreDigest {
 	/// it makes things easier for higher-level users of the chain data to
 	/// be aware of the author of a secondary-slot block.
 	pub authority_index: super::AuthorityIndex,
-	/// Slot number
-	pub slot_number: SlotNumber,
+	/// Slot
+	pub slot: Slot,
 }
 
 /// BABE secondary deterministic slot assignment with VRF outputs.
@@ -59,8 +59,8 @@ pub struct SecondaryPlainPreDigest {
 pub struct SecondaryVRFPreDigest {
 	/// Authority index
 	pub authority_index: super::AuthorityIndex,
-	/// Slot number
-	pub slot_number: SlotNumber,
+	/// Slot
+	pub slot: Slot,
 	/// VRF output
 	pub vrf_output: VRFOutput,
 	/// VRF proof
@@ -93,12 +93,12 @@ impl PreDigest {
 		}
 	}
 
-	/// Returns the slot number of the pre digest.
-	pub fn slot_number(&self) -> SlotNumber {
+	/// Returns the slot of the pre digest.
+	pub fn slot(&self) -> Slot {
 		match self {
-			PreDigest::Primary(primary) => primary.slot_number,
-			PreDigest::SecondaryPlain(secondary) => secondary.slot_number,
-			PreDigest::SecondaryVRF(secondary) => secondary.slot_number,
+			PreDigest::Primary(primary) => primary.slot,
+			PreDigest::SecondaryPlain(secondary) => secondary.slot,
+			PreDigest::SecondaryVRF(secondary) => secondary.slot,
 		}
 	}
 

substrate/primitives/consensus/babe/src/inherents.rs

@@ -31,7 +31,7 @@ use sp_std::result::Result;
 pub const INHERENT_IDENTIFIER: InherentIdentifier = *b"babeslot";
 
 /// The type of the BABE inherent.
-pub type InherentType = u64;
+pub type InherentType = sp_consensus_slots::Slot;
 /// Auxiliary trait to extract BABE inherent data.
 pub trait BabeInherentData {
 	/// Get BABE inherent data.
@@ -82,8 +82,8 @@ impl ProvideInherentData for InherentDataProvider {
 
 	fn provide_inherent_data(&self, inherent_data: &mut InherentData) -> Result<(), Error> {
 		let timestamp = inherent_data.timestamp_inherent_data()?;
-		let slot_number = timestamp / self.slot_duration;
-		inherent_data.put_data(INHERENT_IDENTIFIER, &slot_number)
+		let slot = timestamp / self.slot_duration;
+		inherent_data.put_data(INHERENT_IDENTIFIER, &slot)
 	}
 
 	fn error_to_string(&self, error: &[u8]) -> Option<String> {

substrate/primitives/consensus/babe/src/lib.rs

@@ -76,8 +76,7 @@ pub const MEDIAN_ALGORITHM_CARDINALITY: usize = 1200; // arbitrary suggestion by
 /// The index of an authority.
 pub type AuthorityIndex = u32;
 
-/// A slot number.
-pub use sp_consensus_slots::SlotNumber;
+pub use sp_consensus_slots::Slot;
 
 /// An equivocation proof for multiple block authorships on the same slot (i.e. double vote).
 pub type EquivocationProof<H> = sp_consensus_slots::EquivocationProof<H, AuthorityId>;
@@ -93,11 +92,11 @@ pub type BabeBlockWeight = u32;
 /// Make a VRF transcript from given randomness, slot number and epoch.
 pub fn make_transcript(
 	randomness: &Randomness,
-	slot_number: u64,
+	slot: Slot,
 	epoch: u64,
 ) -> Transcript {
 	let mut transcript = Transcript::new(&BABE_ENGINE_ID);
-	transcript.append_u64(b"slot number", slot_number);
+	transcript.append_u64(b"slot number", *slot);
 	transcript.append_u64(b"current epoch", epoch);
 	transcript.append_message(b"chain randomness", &randomness[..]);
 	transcript
@@ -107,13 +106,13 @@ pub fn make_transcript(
 #[cfg(feature = "std")]
 pub fn make_transcript_data(
 	randomness: &Randomness,
-	slot_number: u64,
+	slot: Slot,
 	epoch: u64,
 ) -> VRFTranscriptData {
 	VRFTranscriptData {
 		label: &BABE_ENGINE_ID,
 		items: vec![
-			("slot number", VRFTranscriptValue::U64(slot_number)),
+			("slot number", VRFTranscriptValue::U64(*slot)),
 			("current epoch", VRFTranscriptValue::U64(epoch)),
 			("chain randomness", VRFTranscriptValue::Bytes(randomness.to_vec())),
 		]
@@ -147,7 +146,7 @@ pub struct BabeGenesisConfigurationV1 {
 	pub slot_duration: u64,
 
 	/// The duration of epochs in slots.
-	pub epoch_length: SlotNumber,
+	pub epoch_length: u64,
 
 	/// A constant value that is used in the threshold calculation formula.
 	/// Expressed as a rational where the first member of the tuple is the
@@ -195,7 +194,7 @@ pub struct BabeGenesisConfiguration {
 	pub slot_duration: u64,
 
 	/// The duration of epochs in slots.
-	pub epoch_length: SlotNumber,
+	pub epoch_length: u64,
 
 	/// A constant value that is used in the threshold calculation formula.
 	/// Expressed as a rational where the first member of the tuple is the
@@ -303,8 +302,8 @@ where
 
 		// both headers must be targetting the same slot and it must
 		// be the same as the one in the proof.
-		if proof.slot_number != first_pre_digest.slot_number() ||
-			first_pre_digest.slot_number() != second_pre_digest.slot_number()
+		if proof.slot != first_pre_digest.slot() ||
+			first_pre_digest.slot() != second_pre_digest.slot()
 		{
 			return None;
 		}
@@ -356,9 +355,9 @@ pub struct Epoch {
 	/// The epoch index.
 	pub epoch_index: u64,
 	/// The starting slot of the epoch.
-	pub start_slot: SlotNumber,
+	pub start_slot: Slot,
 	/// The duration of this epoch.
-	pub duration: SlotNumber,
+	pub duration: u64,
 	/// The authorities and their weights.
 	pub authorities: Vec<(AuthorityId, BabeAuthorityWeight)>,
 	/// Randomness for this epoch.
@@ -376,8 +375,8 @@ sp_api::decl_runtime_apis! {
 		#[changed_in(2)]
 		fn configuration() -> BabeGenesisConfigurationV1;
 
-		/// Returns the slot number that started the current epoch.
-		fn current_epoch_start() -> SlotNumber;
+		/// Returns the slot that started the current epoch.
+		fn current_epoch_start() -> Slot;
 
 		/// Returns information regarding the current epoch.
 		fn current_epoch() -> Epoch;
@@ -391,14 +390,14 @@ sp_api::decl_runtime_apis! {
 		/// session historical module to prove that a given authority key is
 		/// tied to a given staking identity during a specific session. Proofs
 		/// of key ownership are necessary for submitting equivocation reports.
-		/// NOTE: even though the API takes a `slot_number` as parameter the current
+		/// NOTE: even though the API takes a `slot` as parameter the current
 		/// implementations ignores this parameter and instead relies on this
 		/// method being called at the correct block height, i.e. any point at
 		/// which the epoch for the given slot is live on-chain. Future
 		/// implementations will instead use indexed data through an offchain
 		/// worker, not requiring older states to be available.
 		fn generate_key_ownership_proof(
-			slot_number: SlotNumber,
+			slot: Slot,
 			authority_id: AuthorityId,
 		) -> Option<OpaqueKeyOwnershipProof>;
 

substrate/primitives/consensus/slots/Cargo.toml

@@ -15,10 +15,12 @@ targets = ["x86_64-unknown-linux-gnu"]
 [dependencies]
 codec = { package = "parity-scale-codec", version = "1.3.6", default-features = false, features = ["derive"] }
 sp-runtime = { version = "2.0.0", default-features = false, path = "../../runtime" }
+sp-arithmetic = { version = "2.0.0", default-features = false, path = "../../arithmetic" }
 
 [features]
 default = ["std"]
 std = [
 	"codec/std",
 	"sp-runtime/std",
+	"sp-arithmetic/std",
 ]

substrate/primitives/consensus/slots/src/lib.rs

@@ -21,8 +21,76 @@
 
 use codec::{Decode, Encode};
 
-/// A slot number.
-pub type SlotNumber = u64;
+/// Unit type wrapper that represents a slot.
+#[derive(Debug, Encode, Decode, Eq, Clone, Copy, Default, Ord)]
+pub struct Slot(u64);
+
+impl core::ops::Deref for Slot {
+	type Target = u64;
+
+	fn deref(&self) -> &u64 {
+		&self.0
+	}
+}
+
+impl core::ops::Add for Slot {
+	type Output = Self;
+
+	fn add(self, other: Self) -> Self {
+		Self(self.0 + other.0)
+	}
+}
+
+impl core::ops::Add<u64> for Slot {
+	type Output = Self;
+
+	fn add(self, other: u64) -> Self {
+		Self(self.0 + other)
+	}
+}
+
+impl<T: Into<u64> + Copy> core::cmp::PartialEq<T> for Slot {
+	fn eq(&self, eq: &T) -> bool {
+		self.0 == (*eq).into()
+	}
+}
+
+impl<T: Into<u64> + Copy> core::cmp::PartialOrd<T> for Slot {
+	fn partial_cmp(&self, other: &T) -> Option<core::cmp::Ordering> {
+		self.0.partial_cmp(&(*other).into())
+	}
+}
+
+impl Slot {
+	/// Saturating addition.
+	pub fn saturating_add<T: Into<u64>>(self, rhs: T) -> Self {
+		Self(self.0.saturating_add(rhs.into()))
+	}
+
+	/// Saturating subtraction.
+	pub fn saturating_sub<T: Into<u64>>(self, rhs: T) -> Self {
+		Self(self.0.saturating_sub(rhs.into()))
+	}
+}
+
+#[cfg(feature = "std")]
+impl std::fmt::Display for Slot {
+	fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+		write!(f, "{}", self.0)
+	}
+}
+
+impl From<u64> for Slot {
+	fn from(slot: u64) -> Slot {
+		Slot(slot)
+	}
+}
+
+impl From<Slot> for u64 {
+	fn from(slot: Slot) -> u64 {
+		slot.0
+	}
+}
 
 /// Represents an equivocation proof. An equivocation happens when a validator
 /// produces more than one block on the same slot. The proof of equivocation
@@ -32,8 +100,8 @@ pub type SlotNumber = u64;
 pub struct EquivocationProof<Header, Id> {
 	/// Returns the authority id of the equivocator.
 	pub offender: Id,
-	/// The slot number at which the equivocation happened.
-	pub slot_number: SlotNumber,
+	/// The slot at which the equivocation happened.
+	pub slot: Slot,
 	/// The first header involved in the equivocation.
 	pub first_header: Header,
 	/// The second header involved in the equivocation.