PaperMC/paper-server/patches/sources/net/minecraft/util/SpawnUtil.java.patch

--- a/net/minecraft/util/SpawnUtil.java
+++ b/net/minecraft/util/SpawnUtil.java
@@ -21,24 +21,47 @@
     public SpawnUtil() {}
 
     public static <T extends Mob> Optional<T> trySpawnMob(EntityType<T> entityType, EntitySpawnReason reason, ServerLevel world, BlockPos pos, int tries, int horizontalRange, int verticalRange, SpawnUtil.Strategy requirements, boolean requireEmptySpace) {
-        BlockPos.MutableBlockPos blockposition_mutableblockposition = pos.mutable();
+        // CraftBukkit start
+        return SpawnUtil.trySpawnMob(entityType, reason, world, pos, tries, horizontalRange, verticalRange, requirements, requireEmptySpace, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.DEFAULT, null); // Paper - pre creature spawn event
+    }
 
-        for (int l = 0; l < tries; ++l) {
-            int i1 = Mth.randomBetweenInclusive(world.random, -horizontalRange, horizontalRange);
-            int j1 = Mth.randomBetweenInclusive(world.random, -horizontalRange, horizontalRange);
+    public static <T extends Mob> Optional<T> trySpawnMob(EntityType<T> entitytypes, EntitySpawnReason entityspawnreason, ServerLevel worldserver, BlockPos blockposition, int i, int j, int k, SpawnUtil.Strategy spawnutil_a, boolean flag, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason reason, @javax.annotation.Nullable Runnable onAbort) {  // Paper - pre creature spawn event
+        // CraftBukkit end
+        BlockPos.MutableBlockPos blockposition_mutableblockposition = blockposition.mutable();
 
-            blockposition_mutableblockposition.setWithOffset(pos, i1, verticalRange, j1);
-            if (world.getWorldBorder().isWithinBounds((BlockPos) blockposition_mutableblockposition) && SpawnUtil.moveToPossibleSpawnPosition(world, verticalRange, blockposition_mutableblockposition, requirements) && (!requireEmptySpace || world.noCollision(entityType.getSpawnAABB((double) blockposition_mutableblockposition.getX() + 0.5D, (double) blockposition_mutableblockposition.getY(), (double) blockposition_mutableblockposition.getZ() + 0.5D)))) {
-                T t0 = (Mob) entityType.create(world, (Consumer) null, blockposition_mutableblockposition, reason, false, false);
+        for (int l = 0; l < i; ++l) {
+            int i1 = Mth.randomBetweenInclusive(worldserver.random, -j, j);
+            int j1 = Mth.randomBetweenInclusive(worldserver.random, -j, j);
 
+            blockposition_mutableblockposition.setWithOffset(blockposition, i1, k, j1);
+            if (worldserver.getWorldBorder().isWithinBounds((BlockPos) blockposition_mutableblockposition) && SpawnUtil.moveToPossibleSpawnPosition(worldserver, k, blockposition_mutableblockposition, spawnutil_a) && (!flag || worldserver.noCollision(entitytypes.getSpawnAABB((double) blockposition_mutableblockposition.getX() + 0.5D, (double) blockposition_mutableblockposition.getY(), (double) blockposition_mutableblockposition.getZ() + 0.5D)))) {
+                // Paper start - PreCreatureSpawnEvent
+                final com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent event = new com.destroystokyo.paper.event.entity.PreCreatureSpawnEvent(
+                    io.papermc.paper.util.MCUtil.toLocation(worldserver, blockposition),
+                    org.bukkit.craftbukkit.entity.CraftEntityType.minecraftToBukkit(entitytypes),
+                    reason
+                );
+                if (!event.callEvent()) {
+                    if (event.shouldAbortSpawn()) {
+                        if (onAbort != null) {
+                            onAbort.run();
+                        }
+                        return Optional.empty();
+                    }
+                    break;
+                }
+                // Paper end - PreCreatureSpawnEvent
+                T t0 = entitytypes.create(worldserver, (Consumer<T>) null, blockposition_mutableblockposition, entityspawnreason, false, false); // CraftBukkit - decompile error
+
                 if (t0 != null) {
-                    if (t0.checkSpawnRules(world, reason) && t0.checkSpawnObstruction(world)) {
-                        world.addFreshEntityWithPassengers(t0);
+                    if (t0.checkSpawnRules(worldserver, entityspawnreason) && t0.checkSpawnObstruction(worldserver)) {
+                        worldserver.addFreshEntityWithPassengers(t0, reason); // CraftBukkit
+                        if (t0.isRemoved()) return Optional.empty(); // CraftBukkit
                         t0.playAmbientSound();
                         return Optional.of(t0);
                     }
 
-                    t0.discard();
+                    t0.discard(null); // CraftBukkit - add Bukkit remove cause
                 }
             }
         }