FRAME: Fix the Referenda confirming alarm (paritytech#13704)

* Fix the Referenda confirming alarm

* Add minimal regression test

This fails on bf395c8 since the
downwards rounding voids the curve delay.

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

frame/referenda/src/lib.rs

@@ -1206,7 +1206,7 @@ impl<T: Config<I>, I: 'static> Pallet<T, I> {
 			let until_approval = track.min_approval.delay(approval);
 			let until_support = track.min_support.delay(support);
 			let offset = until_support.max(until_approval);
-			deciding.since.saturating_add(offset * track.decision_period)
+			deciding.since.saturating_add(offset.mul_ceil(track.decision_period))
 		})
 	}
 

frame/referenda/src/tests.rs

@@ -286,6 +286,24 @@ fn alarm_interval_works() {
 	});
 }
 
+#[test]
+fn decision_time_is_correct() {
+	new_test_ext().execute_with(|| {
+		let decision_time = |since: u64| {
+			Pallet::<Test>::decision_time(
+				&DecidingStatus { since: since.into(), confirming: None },
+				&Tally { ayes: 100, nays: 5 },
+				TestTracksInfo::tracks()[0].0,
+				&TestTracksInfo::tracks()[0].1,
+			)
+		};
+
+		for i in 0u64..=100 {
+			assert!(decision_time(i) > i, "The decision time should be delayed by the curve");
+		}
+	});
+}
+
 #[test]
 fn auto_timeout_should_happen_with_nothing_but_submit() {
 	new_test_ext().execute_with(|| {