PaperMC/paper-server/nms-patches/net/minecraft/world/level/chunk/IChunkAccess.patch

--- a/net/minecraft/world/level/chunk/IChunkAccess.java
+++ b/net/minecraft/world/level/chunk/IChunkAccess.java
@@ -93,7 +93,11 @@
         }
 
         replaceMissingSections(levelheightaccessor, iregistry, this.sections);
+        // CraftBukkit start
+        this.biomeRegistry = iregistry;
     }
+    public final IRegistry<BiomeBase> biomeRegistry;
+    // CraftBukkit end
 
     private static void replaceMissingSections(LevelHeightAccessor levelheightaccessor, IRegistry<BiomeBase> iregistry, ChunkSection[] achunksection) {
         for (int i = 0; i < achunksection.length; ++i) {
@@ -392,6 +396,27 @@
         }
     }
 
+    // CraftBukkit start
+    public void setBiome(int i, int j, int k, BiomeBase biome) {
+        try {
+            int l = QuartPos.fromBlock(this.getMinBuildHeight());
+            int i1 = l + QuartPos.fromBlock(this.getHeight()) - 1;
+            int j1 = MathHelper.clamp(j, l, i1);
+            int k1 = this.getSectionIndex(QuartPos.toBlock(j1));
+
+            this.sections[k1].setBiome(i & 3, j1 & 3, k & 3, biome);
+        } catch (Throwable throwable) {
+            CrashReport crashreport = CrashReport.forThrowable(throwable, "Setting biome");
+            CrashReportSystemDetails crashreportsystemdetails = crashreport.addCategory("Biome being set");
+
+            crashreportsystemdetails.setDetail("Location", () -> {
+                return CrashReportSystemDetails.formatLocation(this, i, j, k);
+            });
+            throw new ReportedException(crashreport);
+        }
+    }
+    // CraftBukkit end
+
     public void fillBiomesFromNoise(BiomeResolver biomeresolver, Climate.Sampler climate_sampler) {
         ChunkCoordIntPair chunkcoordintpair = this.getPos();
         int i = QuartPos.fromBlock(chunkcoordintpair.getMinBlockX());
@@ -423,8 +448,10 @@
         return this;
     }
 
-    public static final class a extends Record {
+    // CraftBukkit start
+    public static final record a(SerializableTickContainer<Block> blocks, SerializableTickContainer<FluidType> fluids) {
 
+        /*
         private final SerializableTickContainer<Block> blocks;
         private final SerializableTickContainer<FluidType> fluids;
 
@@ -444,6 +471,8 @@
         public final boolean equals(Object object) {
             return this.equals<invokedynamic>(this, object);
         }
+         */
+        // CraftBukkit end
 
         public SerializableTickContainer<Block> blocks() {
             return this.blocks;