pallet-offences: Switch to partition_point (#9049)

This changes the code to use `partition_point` instead of
`binary_search_by_key`, because this was very likely the problematic
pallet 2 weeks ago on polkadot.

substrate/frame/offences/src/tests.rs

@@ -22,7 +22,7 @@
 use super::*;
 use crate::mock::{
 	Offences, System, Offence, Event, KIND, new_test_ext, with_on_offence_fractions,
-	offence_reports,
+	offence_reports, report_id,
 };
 use sp_runtime::Perbill;
 use frame_system::{EventRecord, Phase};
@@ -284,3 +284,62 @@ fn should_properly_count_offences() {
 		);
 	});
 }
+
+/// We insert offences in sorted order using the time slot in the `same_kind_reports`.
+/// This test ensures that it works as expected.
+#[test]
+fn should_properly_sort_offences() {
+	new_test_ext().execute_with(|| {
+		// given
+		let time_slot = 42;
+		assert_eq!(offence_reports(KIND, time_slot), vec![]);
+
+		let offence1 = Offence {
+			validator_set_count: 5,
+			time_slot,
+			offenders: vec![5],
+		};
+		let offence2 = Offence {
+			validator_set_count: 5,
+			time_slot,
+			offenders: vec![4],
+		};
+		let offence3 = Offence {
+			validator_set_count: 5,
+			time_slot: time_slot + 1,
+			offenders: vec![6, 7],
+		};
+		let offence4 = Offence {
+			validator_set_count: 5,
+			time_slot: time_slot - 1,
+			offenders: vec![3],
+		};
+		Offences::report_offence(vec![], offence1).unwrap();
+		with_on_offence_fractions(|f| {
+			assert_eq!(f.clone(), vec![Perbill::from_percent(25)]);
+			f.clear();
+		});
+
+		// when
+		// report for the second time
+		Offences::report_offence(vec![], offence2).unwrap();
+		Offences::report_offence(vec![], offence3).unwrap();
+		Offences::report_offence(vec![], offence4).unwrap();
+
+		// then
+		let same_kind_reports =
+			Vec::<(u128, sp_core::H256)>::decode(
+				&mut &crate::ReportsByKindIndex::<crate::mock::Runtime>::get(KIND)[..],
+			).unwrap();
+		assert_eq!(
+			same_kind_reports,
+			vec![
+				(time_slot - 1, report_id(time_slot - 1, 3)),
+				(time_slot, report_id(time_slot, 5)),
+				(time_slot, report_id(time_slot, 4)),
+				(time_slot + 1, report_id(time_slot + 1, 6)),
+				(time_slot + 1, report_id(time_slot + 1, 7)),
+			]
+		);
+	});
+}