From 541255fe7ea3915cd4b7bb8e50f1af9c2dfec516 Mon Sep 17 00:00:00 2001
From: Pierre Maurice Schwang <mail@pschwang.eu>
Date: Fri, 1 Oct 2021 21:52:30 +0200
Subject: [PATCH] ListFlag#merge should not allow duplicates (Fixes #3157)
 (#3265)

---
 .../plotsquared/core/plot/flag/types/ListFlag.java | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/Core/src/main/java/com/plotsquared/core/plot/flag/types/ListFlag.java b/Core/src/main/java/com/plotsquared/core/plot/flag/types/ListFlag.java
index a4429cb11..2811883ce 100644
--- a/Core/src/main/java/com/plotsquared/core/plot/flag/types/ListFlag.java
+++ b/Core/src/main/java/com/plotsquared/core/plot/flag/types/ListFlag.java
@@ -43,8 +43,18 @@ public abstract class ListFlag<V, F extends PlotFlag<List<V>, F>> extends PlotFl
     @Override
     public F merge(@NonNull List<V> newValue) {
         final List<V> mergedList = new ArrayList<>();
-        mergedList.addAll(getValue());
-        mergedList.addAll(newValue);
+        // If a server already used PS before this fix, we remove all present duplicates on an eventual merge
+        for (final V v : getValue()) {
+            if (!mergedList.contains(v)) {
+                mergedList.add(v);
+            }
+        }
+        // Only add new values if not already present from #getValue()
+        for (final V v : newValue) {
+            if (!mergedList.contains(v)) {
+                mergedList.add(v);
+            }
+        }
         return this.flagOf(mergedList);
     }