core-fellowship: allow infinite demotion period

substrate/frame/core-fellowship/src/lib.rs

@@ -298,6 +298,11 @@ pub mod pallet {
 				let rank_index = Self::rank_to_index(rank).ok_or(Error::<T, I>::InvalidRank)?;
 				params.demotion_period[rank_index]
 			};
+
+			if demotion_period.is_zero() {
+				return Err(Error::<T, I>::NothingDoing.into())
+			}
+
 			let demotion_block = member.last_proof.saturating_add(demotion_period);
 
 			// Ensure enough time has passed.

substrate/frame/core-fellowship/src/tests.rs

@@ -306,6 +306,28 @@ fn offboard_works() {
 	});
 }
 
+#[test]
+fn infinite_demotion_period_works() {
+	new_test_ext().execute_with(|| {
+		let params = ParamsType {
+			active_salary: [10; 9],
+			passive_salary: [10; 9],
+			min_promotion_period: [10; 9],
+			demotion_period: [0; 9],
+			offboard_timeout: 0,
+		};
+		assert_ok!(CoreFellowship::set_params(signed(1), Box::new(params)));
+
+		set_rank(0, 0);
+		assert_ok!(CoreFellowship::import(signed(0)));
+		set_rank(1, 1);
+		assert_ok!(CoreFellowship::import(signed(1)));
+
+		assert_noop!(CoreFellowship::bump(signed(0), 0), Error::<Test>::NothingDoing);
+		assert_noop!(CoreFellowship::bump(signed(0), 1), Error::<Test>::NothingDoing);
+	});
+}
+
 #[test]
 fn proof_postpones_auto_demote() {
 	new_test_ext().execute_with(|| {