Fix vote weights of ranked members in the Society pallet (paritytech#…

…2758)

This PR fixes a bug in the tally accrual of approvals/rejections for
Candidates and Defender. The issue happened because:
- The `match maybe_old` is reducing `weight` from the tally:
```
Some(Vote { approve: true, weight }) => tally.approvals.saturating_reduce(weight),
Some(Vote { approve: false, weight }) => tally.rejections.saturating_reduce(weight),
```
- But `match approval` is accruing only `1` to the tally:
```
true => tally.approvals.saturating_accrue(1),
false => tally.rejections.saturating_accrue(1),
```

This way, if a member is rank 1 his vote is going to have weight 1 when
accruing but weight 4 when reducing from the tally. For example, let's
say:
- There's a Candidate with 0 approvals and 12 rejections;
- A ranked Member votes against the Candidate;
- The tally changes to 0 approvals and 13 rejections (should be 16);
- The Member changes his vote to an approval;
- Now tally changes to 1 approvals and 9 rejections, removing the
accrued approvals from other Members;
- If the Member keeps changing his vote, it wipes the tally clean.

So this PR changes `match approval` to accrue `weight` instead of just
`1` and changes the tests:
- Fixes `challenges_work`. This test started failing after the fix. The
reason is that the test assumes that all Members have equal weights to
their votes, but Member 10 is ranked, so his vote should have weight 4
against the Defender. So instead of using Member 10, I added Member 50
of rank 0 to keep the same logic;
- Improves `votes_are_working`. Added some assertions to check if the
tally is correct even after a ranked Member changes his vote a couple
times;
- Fixes `waive_repay_works`. Unrelated to the bug, but this test was
yielding a false positive. The test is ranking up Member 20, but
asserting the rank of Member 10, which is already ranked up.

---------

Co-authored-by: Bastian Köcher <[email protected]>
Co-authored-by: command-bot <>

substrate/frame/society/src/lib.rs

@@ -1433,8 +1433,8 @@ impl<T: Config<I>, I: 'static> Pallet<T, I> {
 		let weight_root = rank + 1;
 		let weight = weight_root * weight_root;
 		match approve {
-			true => tally.approvals.saturating_accrue(1),
-			false => tally.rejections.saturating_accrue(1),
+			true => tally.approvals.saturating_accrue(weight),
+			false => tally.rejections.saturating_accrue(weight),
 		}
 		Vote { approve, weight }
 	}

substrate/frame/society/src/tests.rs

@@ -720,7 +720,7 @@ fn unvouch_works() {
 		// But their pick doesn't resign (yet).
 		conclude_intake(false, None);
 		// Voting still happening and voucher cannot unvouch.
-		assert_eq!(candidacies(), vec![(20, candidacy(1, 100, Vouch(10, 0), 0, 1))]);
+		assert_eq!(candidacies(), vec![(20, candidacy(1, 100, Vouch(10, 0), 0, 4))]);
 		assert_eq!(Members::<Test>::get(10).unwrap().vouching, Some(VouchingStatus::Vouching));
 
 		// Candidate gives in and resigns.
@@ -836,72 +836,72 @@ fn founder_and_head_cannot_be_removed() {
 fn challenges_work() {
 	EnvBuilder::new().execute(|| {
 		// Add some members
-		place_members([20, 30, 40]);
+		place_members([20, 30, 40, 50]);
 		// Votes are empty
-		assert_eq!(DefenderVotes::<Test>::get(0, 10), None);
 		assert_eq!(DefenderVotes::<Test>::get(0, 20), None);
 		assert_eq!(DefenderVotes::<Test>::get(0, 30), None);
 		assert_eq!(DefenderVotes::<Test>::get(0, 40), None);
+		assert_eq!(DefenderVotes::<Test>::get(0, 50), None);
 		// Check starting point
-		assert_eq!(members(), vec![10, 20, 30, 40]);
+		assert_eq!(members(), vec![10, 20, 30, 40, 50]);
 		assert_eq!(Defending::<Test>::get(), None);
 
-		// 30 will be challenged during the challenge rotation
+		// 40 will be challenged during the challenge rotation
 		next_challenge();
-		assert_eq!(Defending::<Test>::get().unwrap().0, 30);
+		assert_eq!(Defending::<Test>::get().unwrap().0, 40);
 		// They can always free vote for themselves
-		assert_ok!(Society::defender_vote(Origin::signed(30), true));
+		assert_ok!(Society::defender_vote(Origin::signed(40), true));
 
 		// If no one else votes, nothing happens
 		next_challenge();
-		assert_eq!(members(), vec![10, 20, 30, 40]);
+		assert_eq!(members(), vec![10, 20, 30, 40, 50]);
 		// Reset votes for last challenge
 		assert_ok!(Society::cleanup_challenge(Origin::signed(0), 0, 10));
-		// New challenge period
-		assert_eq!(Defending::<Test>::get().unwrap().0, 30);
+		// New challenge period, 20 is challenged
+		assert_eq!(Defending::<Test>::get().unwrap().0, 20);
 		// Non-member cannot vote
 		assert_noop!(Society::defender_vote(Origin::signed(1), true), Error::<Test>::NotMember);
 		// 3 people say accept, 1 reject
-		assert_ok!(Society::defender_vote(Origin::signed(10), true));
 		assert_ok!(Society::defender_vote(Origin::signed(20), true));
 		assert_ok!(Society::defender_vote(Origin::signed(30), true));
-		assert_ok!(Society::defender_vote(Origin::signed(40), false));
+		assert_ok!(Society::defender_vote(Origin::signed(40), true));
+		assert_ok!(Society::defender_vote(Origin::signed(50), false));
 
 		next_challenge();
-		// 30 survives
-		assert_eq!(members(), vec![10, 20, 30, 40]);
+		// 20 survives
+		assert_eq!(members(), vec![10, 20, 30, 40, 50]);
 		// Reset votes for last challenge
 		assert_ok!(Society::cleanup_challenge(Origin::signed(0), 1, 10));
 		// Votes are reset
-		assert_eq!(DefenderVotes::<Test>::get(0, 10), None);
 		assert_eq!(DefenderVotes::<Test>::get(0, 20), None);
 		assert_eq!(DefenderVotes::<Test>::get(0, 30), None);
 		assert_eq!(DefenderVotes::<Test>::get(0, 40), None);
+		assert_eq!(DefenderVotes::<Test>::get(0, 50), None);
 
-		// One more time
-		assert_eq!(Defending::<Test>::get().unwrap().0, 30);
+		// One more time, 40 is challenged
+		assert_eq!(Defending::<Test>::get().unwrap().0, 40);
 		// 2 people say accept, 2 reject
-		assert_ok!(Society::defender_vote(Origin::signed(10), true));
 		assert_ok!(Society::defender_vote(Origin::signed(20), true));
-		assert_ok!(Society::defender_vote(Origin::signed(30), false));
+		assert_ok!(Society::defender_vote(Origin::signed(30), true));
 		assert_ok!(Society::defender_vote(Origin::signed(40), false));
+		assert_ok!(Society::defender_vote(Origin::signed(50), false));
 
 		next_challenge();
-		// 30 is suspended
-		assert_eq!(members(), vec![10, 20, 40]);
+		// 40 is suspended
+		assert_eq!(members(), vec![10, 20, 30, 50]);
 		assert_eq!(
-			SuspendedMembers::<Test>::get(30),
-			Some(MemberRecord { rank: 0, strikes: 0, vouching: None, index: 2 })
+			SuspendedMembers::<Test>::get(40),
+			Some(MemberRecord { rank: 0, strikes: 0, vouching: None, index: 3 })
 		);
 		// Reset votes for last challenge
 		assert_ok!(Society::cleanup_challenge(Origin::signed(0), 2, 10));
-		// New defender is chosen
-		assert_eq!(Defending::<Test>::get().unwrap().0, 20);
+		// New defender is chosen, 30 is challenged
+		assert_eq!(Defending::<Test>::get().unwrap().0, 30);
 		// Votes are reset
-		assert_eq!(DefenderVotes::<Test>::get(0, 10), None);
 		assert_eq!(DefenderVotes::<Test>::get(0, 20), None);
 		assert_eq!(DefenderVotes::<Test>::get(0, 30), None);
 		assert_eq!(DefenderVotes::<Test>::get(0, 40), None);
+		assert_eq!(DefenderVotes::<Test>::get(0, 50), None);
 	});
 }
 
@@ -1044,6 +1044,9 @@ fn vouching_handles_removed_member_with_candidate() {
 fn votes_are_working() {
 	EnvBuilder::new().execute(|| {
 		place_members([20]);
+		// Member 10 is rank 1 and Member 20 is rank 0
+		assert_eq!(Members::<Test>::get(10).unwrap().rank, 1);
+		assert_eq!(Members::<Test>::get(20).unwrap().rank, 0);
 		// Users make bids of various amounts
 		assert_ok!(Society::bid(RuntimeOrigin::signed(50), 500));
 		assert_ok!(Society::bid(RuntimeOrigin::signed(40), 400));
@@ -1061,6 +1064,32 @@ fn votes_are_working() {
 		assert_eq!(Votes::<Test>::get(30, 20), Some(Vote { approve: true, weight: 1 }));
 		assert_eq!(Votes::<Test>::get(40, 10), Some(Vote { approve: true, weight: 4 }));
 		assert_eq!(Votes::<Test>::get(50, 10), None);
+
+		// Votes have correct weights on the tally
+		assert_eq!(
+			Candidates::<Test>::get(30).unwrap().tally,
+			Tally { approvals: 5, rejections: 0 }
+		);
+		assert_eq!(
+			Candidates::<Test>::get(40).unwrap().tally,
+			Tally { approvals: 4, rejections: 0 }
+		);
+		// Member 10 changes his vote for Candidate 30
+		assert_ok!(Society::vote(Origin::signed(10), 30, false));
+		// Assert the tally calculation is correct
+		assert_eq!(
+			Candidates::<Test>::get(30).unwrap().tally,
+			Tally { approvals: 1, rejections: 4 }
+		);
+		// Member 10 changes his vote again
+		assert_ok!(Society::vote(Origin::signed(10), 30, true));
+		// Assert the tally is still correct
+		assert_eq!(
+			Candidates::<Test>::get(30).unwrap().tally,
+			Tally { approvals: 5, rejections: 0 }
+		);
+
+		// Finish intake
 		conclude_intake(false, None);
 		// Cleanup the candidacy
 		assert_ok!(Society::cleanup_candidacy(Origin::signed(0), 30, 10));
@@ -1240,7 +1269,7 @@ fn waive_repay_works() {
 			Payouts::<Test>::get(20),
 			PayoutRecord { paid: 0, payouts: vec![].try_into().unwrap() }
 		);
-		assert_eq!(Members::<Test>::get(10).unwrap().rank, 1);
+		assert_eq!(Members::<Test>::get(20).unwrap().rank, 1);
 		assert_eq!(Balances::free_balance(20), 50);
 	});
 }