From aa5e6b456e1681a51bed39c66ef942fdde3be8c6 Mon Sep 17 00:00:00 2001
From: Matthew Chen <matthew@signal.org>
Date: Mon, 5 Nov 2018 08:58:22 -0500
Subject: [PATCH] Preserve ordering in incremental diffs.

---
 .../ConversationView/ConversationViewModel.m             | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/Signal/src/ViewControllers/ConversationView/ConversationViewModel.m b/Signal/src/ViewControllers/ConversationView/ConversationViewModel.m
index a557e7805..d5a46e05c 100644
--- a/Signal/src/ViewControllers/ConversationView/ConversationViewModel.m
+++ b/Signal/src/ViewControllers/ConversationView/ConversationViewModel.m
@@ -654,13 +654,12 @@ static const int kYapDatabaseRangeMinLength = 0;
     NSSet<NSString *> *newItemIdSet = [NSSet setWithArray:newItemIdList];
 
     // We use sets and dictionaries here to ensure perf.
-    NSMutableSet<NSString *> *deletedItemIdSet = [oldItemIdSet mutableCopy];
+    NSMutableOrderedSet<NSString *> *deletedItemIdSet = [NSMutableOrderedSet orderedSetWithArray:oldItemIdList];
     [deletedItemIdSet minusSet:newItemIdSet];
-    NSMutableSet<NSString *> *insertedItemIdSet = [newItemIdSet mutableCopy];
+    NSMutableOrderedSet<NSString *> *insertedItemIdSet = [NSMutableOrderedSet orderedSetWithArray:newItemIdList];
     [insertedItemIdSet minusSet:oldItemIdSet];
-    NSArray<NSString *> *deletedItemIdList = [deletedItemIdSet.allObjects sortedArrayUsingSelector:@selector(compare:)];
-    NSArray<NSString *> *insertedItemIdList =
-        [insertedItemIdSet.allObjects sortedArrayUsingSelector:@selector(compare:)];
+    NSArray<NSString *> *deletedItemIdList = [deletedItemIdSet.array copy];
+    NSArray<NSString *> *insertedItemIdList = [insertedItemIdSet.array copy];
 
     // Try to generate a series of "update items" that safely transform
     // the "old item list" into the "new item list".