From 5189a7401071629af5b011cc8d4b5c61322125e7 Mon Sep 17 00:00:00 2001
From: RunasSudo <runassudo@yingtongli.me>
Date: Sun, 30 May 2021 18:27:28 +1000
Subject: [PATCH] Fix bug when excluding candidate with 0 votes

---
 src/stv/mod.rs | 88 ++++++++++++++++++++++++++------------------------
 1 file changed, 46 insertions(+), 42 deletions(-)

diff --git a/src/stv/mod.rs b/src/stv/mod.rs
index 901aabd..3cd5134 100644
--- a/src/stv/mod.rs
+++ b/src/stv/mod.rs
@@ -445,53 +445,57 @@ where
 		panic!("Invalid --exclusion");
 	}
 	
-	let value = &votes[0].value / &votes[0].ballot.orig_value;
-	
-	// Count next preferences
-	let result = next_preferences(state, votes);
-	
-	if opts.exclusion == "one_round" {
-		state.logger.log_literal(format!("Transferring {:.0} ballot papers, totalling {:.2} votes.", result.total_ballots, result.total_votes));
-	} else if opts.exclusion == "by_value" {
-		state.logger.log_literal(format!("Transferring {:.0} ballot papers, totalling {:.2} votes, received at value {:.2}.", result.total_ballots, result.total_votes, value));
-	}
-	
-	// Transfer candidate votes
 	let mut checksum = N::new();
 	
-	for (candidate, entry) in result.candidates.into_iter() {
-		let parcel = entry.votes as Parcel<N>;
-		let count_card = state.candidates.get_mut(candidate).unwrap();
-		count_card.parcels.push(parcel);
+	if votes.len() > 0 {
+		let value = &votes[0].value / &votes[0].ballot.orig_value;
 		
-		// Round transfers
-		let mut candidate_transfers = entry.num_votes;
-		if let Some(dps) = opts.round_votes {
-			candidate_transfers.floor_mut(dps);
+		// Count next preferences
+		let result = next_preferences(state, votes);
+		
+		if opts.exclusion == "one_round" {
+			state.logger.log_literal(format!("Transferring {:.0} ballot papers, totalling {:.2} votes.", result.total_ballots, result.total_votes));
+		} else if opts.exclusion == "by_value" {
+			state.logger.log_literal(format!("Transferring {:.0} ballot papers, totalling {:.2} votes, received at value {:.2}.", result.total_ballots, result.total_votes, value));
 		}
-		count_card.transfer(&candidate_transfers);
-		checksum += candidate_transfers;
-	}
-	
-	// Transfer exhausted votes
-	let parcel = result.exhausted.votes as Parcel<N>;
-	state.exhausted.parcels.push(parcel);
-	
-	let mut exhausted_transfers = result.exhausted.num_votes;
-	if let Some(dps) = opts.round_votes {
-		exhausted_transfers.floor_mut(dps);
-	}
-	state.exhausted.transfer(&exhausted_transfers);
-	checksum += exhausted_transfers;
-	
-	if votes_remaining > 0 {
-		// Subtract from candidate tally
-		let count_card = state.candidates.get_mut(excluded_candidate).unwrap();
-		checksum -= &result.total_votes;
-		count_card.transfer(&-result.total_votes);
 		
-		// By definition, there is no loss by fraction
-	} else {
+		// Transfer candidate votes
+		for (candidate, entry) in result.candidates.into_iter() {
+			let parcel = entry.votes as Parcel<N>;
+			let count_card = state.candidates.get_mut(candidate).unwrap();
+			count_card.parcels.push(parcel);
+			
+			// Round transfers
+			let mut candidate_transfers = entry.num_votes;
+			if let Some(dps) = opts.round_votes {
+				candidate_transfers.floor_mut(dps);
+			}
+			count_card.transfer(&candidate_transfers);
+			checksum += candidate_transfers;
+		}
+		
+		// Transfer exhausted votes
+		let parcel = result.exhausted.votes as Parcel<N>;
+		state.exhausted.parcels.push(parcel);
+		
+		let mut exhausted_transfers = result.exhausted.num_votes;
+		if let Some(dps) = opts.round_votes {
+			exhausted_transfers.floor_mut(dps);
+		}
+		state.exhausted.transfer(&exhausted_transfers);
+		checksum += exhausted_transfers;
+		
+		if votes_remaining > 0 {
+			// Subtract from candidate tally
+			let count_card = state.candidates.get_mut(excluded_candidate).unwrap();
+			checksum -= &result.total_votes;
+			count_card.transfer(&-result.total_votes);
+			
+			// By definition, there is no loss by fraction
+		}
+	}
+	
+	if votes_remaining == 0 {
 		// Finalise candidate votes
 		let count_card = state.candidates.get_mut(excluded_candidate).unwrap();
 		checksum -= &count_card.votes;