From 7f160903951732e205d3a202bc18b092b4a7778d Mon Sep 17 00:00:00 2001
From: RunasSudo <runassudo@yingtongli.me>
Date: Mon, 19 Jul 2021 18:35:23 +1000
Subject: [PATCH] Fix crash on attempting segmented exclusion of candidate with
 no votes

---
 src/stv/gregory.rs | 86 ++++++++++++++++++++++++++--------------------
 1 file changed, 49 insertions(+), 37 deletions(-)

diff --git a/src/stv/gregory.rs b/src/stv/gregory.rs
index 6f604dd..45a0b50 100644
--- a/src/stv/gregory.rs
+++ b/src/stv/gregory.rs
@@ -391,42 +391,49 @@ where
 		}
 		ExclusionMethod::ByValue => {
 			// Exclude by value
-			let max_value = excluded_candidates.iter()
-				.map(|c| state.candidates[c].parcels.iter()
-					.map(|p| p.iter().map(|v| &v.value / &v.ballot.orig_value).max().unwrap())
-					.max().unwrap())
-				.max().unwrap();
+			let excluded_with_votes: Vec<&&Candidate> = excluded_candidates.iter().filter(|c| !state.candidates[*c].parcels.is_empty()).collect();
 			
-			votes_remain = false;
-			
-			for excluded_candidate in excluded_candidates.iter() {
-				let count_card = state.candidates.get_mut(excluded_candidate).unwrap();
+			if excluded_with_votes.is_empty() {
+				votes_remain = false;
+			} else {
+				// If candidates to exclude still having votes, select only those with the greatest value
+				let max_value = excluded_with_votes.iter()
+					.map(|c| state.candidates[*c].parcels.iter()
+						.map(|p| p.iter().map(|v| &v.value / &v.ballot.orig_value).max().unwrap())
+						.max().unwrap())
+					.max().unwrap();
 				
-				// Filter out just those votes with max_value
-				let mut remaining_votes = Vec::new();
+				votes_remain = false;
 				
-				let cand_votes = count_card.parcels.concat();
-				
-				let mut votes_transferred = N::new();
-				for vote in cand_votes.into_iter() {
-					if &vote.value / &vote.ballot.orig_value == max_value {
-						votes_transferred += &vote.value;
-						votes.push(vote);
-					} else {
-						remaining_votes.push(vote);
+				for excluded_candidate in excluded_with_votes.iter() {
+					let count_card = state.candidates.get_mut(*excluded_candidate).unwrap();
+					
+					// Filter out just those votes with max_value
+					let mut remaining_votes = Vec::new();
+					
+					let cand_votes = count_card.parcels.concat();
+					
+					let mut votes_transferred = N::new();
+					for vote in cand_votes.into_iter() {
+						if &vote.value / &vote.ballot.orig_value == max_value {
+							votes_transferred += &vote.value;
+							votes.push(vote);
+						} else {
+							remaining_votes.push(vote);
+						}
 					}
+					
+					if !remaining_votes.is_empty() {
+						votes_remain = true;
+					}
+					
+					// Leave remaining votes with candidate (as one parcel)
+					count_card.parcels = vec![remaining_votes];
+					
+					// Update votes
+					checksum -= &votes_transferred;
+					count_card.transfer(&-votes_transferred);
 				}
-				
-				if !remaining_votes.is_empty() {
-					votes_remain = true;
-				}
-				
-				// Leave remaining votes with candidate (as one parcel)
-				count_card.parcels = vec![remaining_votes];
-				
-				// Update votes
-				checksum -= &votes_transferred;
-				count_card.transfer(&-votes_transferred);
 			}
 		}
 		ExclusionMethod::ParcelsByOrder => {
@@ -436,13 +443,18 @@ where
 			}
 			
 			let count_card = state.candidates.get_mut(excluded_candidates[0]).unwrap();
-			votes = count_card.parcels.remove(0);
-			votes_remain = !count_card.parcels.is_empty();
 			
-			// Update votes
-			let votes_transferred = votes.iter().fold(N::new(), |acc, v| acc + &v.value);
-			checksum -= &votes_transferred;
-			count_card.transfer(&-votes_transferred);
+			if count_card.parcels.is_empty() {
+				votes_remain = false;
+			} else {
+				votes = count_card.parcels.remove(0);
+				votes_remain = !count_card.parcels.is_empty();
+				
+				// Update votes
+				let votes_transferred = votes.iter().fold(N::new(), |acc, v| acc + &v.value);
+				checksum -= &votes_transferred;
+				count_card.transfer(&-votes_transferred);
+			}
 		}
 		_ => panic!()
 	}