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/client/consensus/slots/src/aux_schema.rs

@@ -21,7 +21,7 @@
 use codec::{Encode, Decode};
 use sc_client_api::backend::AuxStore;
 use sp_blockchain::{Result as ClientResult, Error as ClientError};
-use sp_consensus_slots::EquivocationProof;
+use sp_consensus_slots::{EquivocationProof, Slot};
 use sp_runtime::traits::Header;
 
 const SLOT_HEADER_MAP_KEY: &[u8] = b"slot_header_map";
@@ -52,8 +52,8 @@ fn load_decode<C, T>(backend: &C, key: &[u8]) -> ClientResult<Option<T>>
 /// Note: it detects equivocations only when slot_now - slot <= MAX_SLOT_CAPACITY.
 pub fn check_equivocation<C, H, P>(
 	backend: &C,
-	slot_now: u64,
-	slot: u64,
+	slot_now: Slot,
+	slot: Slot,
 	header: &H,
 	signer: &P,
 ) -> ClientResult<Option<EquivocationProof<H, P>>>
@@ -63,7 +63,7 @@ pub fn check_equivocation<C, H, P>(
 		P: Clone + Encode + Decode + PartialEq,
 {
 	// We don't check equivocations for old headers out of our capacity.
-	if slot_now.saturating_sub(slot) > MAX_SLOT_CAPACITY {
+	if slot_now.saturating_sub(*slot) > Slot::from(MAX_SLOT_CAPACITY) {
 		return Ok(None);
 	}
 
@@ -77,7 +77,7 @@ pub fn check_equivocation<C, H, P>(
 
 	// Get first slot saved.
 	let slot_header_start = SLOT_HEADER_START.to_vec();
-	let first_saved_slot = load_decode::<_, u64>(backend, &slot_header_start[..])?
+	let first_saved_slot = load_decode::<_, Slot>(backend, &slot_header_start[..])?
 		.unwrap_or(slot);
 
 	if slot_now < first_saved_slot {
@@ -92,7 +92,7 @@ pub fn check_equivocation<C, H, P>(
 			// 2) with different hash
 			if header.hash() != prev_header.hash() {
 				return Ok(Some(EquivocationProof {
-					slot_number: slot,
+					slot,
 					offender: signer.clone(),
 					first_header: prev_header.clone(),
 					second_header: header.clone(),
@@ -109,11 +109,11 @@ pub fn check_equivocation<C, H, P>(
 	let mut keys_to_delete = vec![];
 	let mut new_first_saved_slot = first_saved_slot;
 
-	if slot_now - first_saved_slot >= PRUNING_BOUND {
+	if *slot_now - *first_saved_slot >= PRUNING_BOUND {
 		let prefix = SLOT_HEADER_MAP_KEY.to_vec();
 		new_first_saved_slot = slot_now.saturating_sub(MAX_SLOT_CAPACITY);
 
-		for s in first_saved_slot..new_first_saved_slot {
+		for s in u64::from(first_saved_slot)..new_first_saved_slot.into() {
 			let mut p = prefix.clone();
 			s.using_encoded(|s| p.extend(s));
 			keys_to_delete.push(p);
@@ -174,8 +174,8 @@ mod test {
 		assert!(
 			check_equivocation(
 				&client,
-				2,
-				2,
+				2.into(),
+				2.into(),
 				&header1,
 				&public,
 			).unwrap().is_none(),
@@ -184,8 +184,8 @@ mod test {
 		assert!(
 			check_equivocation(
 				&client,
-				3,
-				2,
+				3.into(),
+				2.into(),
 				&header1,
 				&public,
 			).unwrap().is_none(),
@@ -195,8 +195,8 @@ mod test {
 		assert!(
 			check_equivocation(
 				&client,
-				4,
-				2,
+				4.into(),
+				2.into(),
 				&header2,
 				&public,
 			).unwrap().is_some(),
@@ -206,8 +206,8 @@ mod test {
 		assert!(
 			check_equivocation(
 				&client,
-				5,
-				4,
+				5.into(),
+				4.into(),
 				&header3,
 				&public,
 			).unwrap().is_none(),
@@ -217,8 +217,8 @@ mod test {
 		assert!(
 			check_equivocation(
 				&client,
-				PRUNING_BOUND + 2,
-				MAX_SLOT_CAPACITY + 4,
+				(PRUNING_BOUND + 2).into(),
+				(MAX_SLOT_CAPACITY + 4).into(),
 				&header4,
 				&public,
 			).unwrap().is_none(),
@@ -228,8 +228,8 @@ mod test {
 		assert!(
 			check_equivocation(
 				&client,
-				PRUNING_BOUND + 3,
-				MAX_SLOT_CAPACITY + 4,
+				(PRUNING_BOUND + 3).into(),
+				(MAX_SLOT_CAPACITY + 4).into(),
 				&header5,
 				&public,
 			).unwrap().is_some(),
@@ -239,8 +239,8 @@ mod test {
 		assert!(
 			check_equivocation(
 				&client,
-				PRUNING_BOUND + 4,
-				4,
+				(PRUNING_BOUND + 4).into(),
+				4.into(),
 				&header6,
 				&public,
 			).unwrap().is_none(),