Paper/paper-server/nms-patches/net/minecraft/server/level/PlayerChunk.patch

--- a/net/minecraft/server/level/PlayerChunk.java
+++ b/net/minecraft/server/level/PlayerChunk.java
@@ -37,6 +37,10 @@
 import net.minecraft.world.level.chunk.ProtoChunkExtension;
 import net.minecraft.world.level.lighting.LightEngine;
 
+// CraftBukkit start
+import net.minecraft.server.MinecraftServer;
+// CraftBukkit end
+
 public class PlayerChunk {
 
     public static final Either<IChunkAccess, PlayerChunk.Failure> UNLOADED_CHUNK = Either.right(PlayerChunk.Failure.UNLOADED);
@@ -75,11 +79,11 @@
         this.fullChunkFuture = PlayerChunk.UNLOADED_LEVEL_CHUNK_FUTURE;
         this.tickingChunkFuture = PlayerChunk.UNLOADED_LEVEL_CHUNK_FUTURE;
         this.entityTickingChunkFuture = PlayerChunk.UNLOADED_LEVEL_CHUNK_FUTURE;
-        this.chunkToSave = CompletableFuture.completedFuture((Object) null);
+        this.chunkToSave = CompletableFuture.completedFuture(null); // CraftBukkit - decompile error
         this.chunkToSaveHistory = null;
         this.blockChangedLightSectionFilter = new BitSet();
         this.skyChangedLightSectionFilter = new BitSet();
-        this.pendingFullStateConfirmation = CompletableFuture.completedFuture((Object) null);
+        this.pendingFullStateConfirmation = CompletableFuture.completedFuture(null); // CraftBukkit - decompile error
         this.pos = chunkcoordintpair;
         this.levelHeightAccessor = levelheightaccessor;
         this.lightEngine = lightengine;
@@ -117,17 +121,17 @@
     @Nullable
     public Chunk getTickingChunk() {
         CompletableFuture<Either<Chunk, PlayerChunk.Failure>> completablefuture = this.getTickingChunkFuture();
-        Either<Chunk, PlayerChunk.Failure> either = (Either) completablefuture.getNow((Object) null);
+        Either<Chunk, PlayerChunk.Failure> either = (Either) completablefuture.getNow(null); // CraftBukkit - decompile error
 
-        return either == null ? null : (Chunk) either.left().orElse((Object) null);
+        return either == null ? null : (Chunk) either.left().orElse(null); // CraftBukkit - decompile error
     }
 
     @Nullable
     public Chunk getFullChunk() {
         CompletableFuture<Either<Chunk, PlayerChunk.Failure>> completablefuture = this.getFullChunkFuture();
-        Either<Chunk, PlayerChunk.Failure> either = (Either) completablefuture.getNow((Object) null);
+        Either<Chunk, PlayerChunk.Failure> either = (Either) completablefuture.getNow(null); // CraftBukkit - decompile error
 
-        return either == null ? null : (Chunk) either.left().orElse((Object) null);
+        return either == null ? null : (Chunk) either.left().orElse(null); // CraftBukkit - decompile error
     }
 
     @Nullable
@@ -172,6 +176,7 @@
         if (chunk != null) {
             int i = this.levelHeightAccessor.getSectionIndex(blockposition.getY());
 
+            if (i < 0 || i >= this.changedBlocksPerSection.length) return; // CraftBukkit - SPIGOT-6086, SPIGOT-6296
             if (this.changedBlocksPerSection[i] == null) {
                 this.hasChangedSections = true;
                 this.changedBlocksPerSection[i] = new ShortOpenHashSet();
@@ -368,7 +373,7 @@
         this.pendingFullStateConfirmation = completablefuture1;
         completablefuture.thenAccept((either) -> {
             either.ifLeft((chunk) -> {
-                completablefuture1.complete((Object) null);
+                completablefuture1.complete(null); // CraftBukkit - decompile error
             });
         });
     }
@@ -385,6 +390,30 @@
         boolean flag1 = this.ticketLevel <= PlayerChunkMap.MAX_CHUNK_DISTANCE;
         PlayerChunk.State playerchunk_state = getFullChunkStatus(this.oldTicketLevel);
         PlayerChunk.State playerchunk_state1 = getFullChunkStatus(this.ticketLevel);
+        // CraftBukkit start
+        // ChunkUnloadEvent: Called before the chunk is unloaded: isChunkLoaded is still true and chunk can still be modified by plugins.
+        if (playerchunk_state.isOrAfter(PlayerChunk.State.BORDER) && !playerchunk_state1.isOrAfter(PlayerChunk.State.BORDER)) {
+            this.getFutureIfPresentUnchecked(ChunkStatus.FULL).thenAccept((either) -> {
+                Chunk chunk = (Chunk)either.left().orElse(null);
+                if (chunk != null) {
+                    playerchunkmap.callbackExecutor.execute(() -> {
+                        // Minecraft will apply the chunks tick lists to the world once the chunk got loaded, and then store the tick
+                        // lists again inside the chunk once the chunk becomes inaccessible and set the chunk's needsSaving flag.
+                        // These actions may however happen deferred, so we manually set the needsSaving flag already here.
+                        chunk.setUnsaved(true);
+                        chunk.unloadCallback();
+                    });
+                }
+            }).exceptionally((throwable) -> {
+                // ensure exceptions are printed, by default this is not the case
+                MinecraftServer.LOGGER.error("Failed to schedule unload callback for chunk " + PlayerChunk.this.pos, throwable);
+                return null;
+            });
+
+            // Run callback right away if the future was already done
+            playerchunkmap.callbackExecutor.run();
+        }
+        // CraftBukkit end
 
         if (flag) {
             Either<IChunkAccess, PlayerChunk.Failure> either = Either.right(new PlayerChunk.Failure() {
@@ -455,6 +484,26 @@
 
         this.onLevelChange.onLevelChange(this.pos, this::getQueueLevel, this.ticketLevel, this::setQueueLevel);
         this.oldTicketLevel = this.ticketLevel;
+        // CraftBukkit start
+        // ChunkLoadEvent: Called after the chunk is loaded: isChunkLoaded returns true and chunk is ready to be modified by plugins.
+        if (!playerchunk_state.isOrAfter(PlayerChunk.State.BORDER) && playerchunk_state1.isOrAfter(PlayerChunk.State.BORDER)) {
+            this.getFutureIfPresentUnchecked(ChunkStatus.FULL).thenAccept((either) -> {
+                Chunk chunk = (Chunk)either.left().orElse(null);
+                if (chunk != null) {
+                    playerchunkmap.callbackExecutor.execute(() -> {
+                        chunk.loadCallback();
+                    });
+                }
+            }).exceptionally((throwable) -> {
+                // ensure exceptions are printed, by default this is not the case
+                MinecraftServer.LOGGER.error("Failed to schedule load callback for chunk " + PlayerChunk.this.pos, throwable);
+                return null;
+            });
+
+            // Run callback right away if the future was already done
+            playerchunkmap.callbackExecutor.run();
+        }
+        // CraftBukkit end
     }
 
     public static ChunkStatus getStatus(int i) {