papermc/paper-server/nms-patches/net/minecraft/world/level/Explosion.patch

--- a/net/minecraft/world/level/Explosion.java
+++ b/net/minecraft/world/level/Explosion.java
@@ -40,6 +40,15 @@
 import net.minecraft.world.phys.MovingObjectPosition;
 import net.minecraft.world.phys.Vec3D;
 
+// CraftBukkit start
+import net.minecraft.world.entity.boss.EntityComplexPart;
+import net.minecraft.world.entity.boss.enderdragon.EntityEnderDragon;
+import org.bukkit.craftbukkit.event.CraftEventFactory;
+import org.bukkit.event.entity.EntityExplodeEvent;
+import org.bukkit.Location;
+import org.bukkit.event.block.BlockExplodeEvent;
+// CraftBukkit end
+
 public class Explosion {
 
     private static final ExplosionDamageCalculator EXPLOSION_DAMAGE_CALCULATOR = new ExplosionDamageCalculator();
@@ -58,6 +67,7 @@
     private final ExplosionDamageCalculator damageCalculator;
     private final ObjectArrayList<BlockPosition> toBlow;
     private final Map<EntityHuman, Vec3D> hitPlayers;
+    public boolean wasCanceled = false; // CraftBukkit - add field
 
     public Explosion(World world, @Nullable Entity entity, double d0, double d1, double d2, float f, List<BlockPosition> list) {
         this(world, entity, d0, d1, d2, f, false, Explosion.Effect.DESTROY_WITH_DECAY, list);
@@ -78,7 +88,7 @@
         this.hitPlayers = Maps.newHashMap();
         this.level = world;
         this.source = entity;
-        this.radius = f;
+        this.radius = (float) Math.max(f, 0.0); // CraftBukkit - clamp bad values
         this.x = d0;
         this.y = d1;
         this.z = d2;
@@ -128,6 +138,11 @@
     }
 
     public void explode() {
+        // CraftBukkit start
+        if (this.radius < 0.1F) {
+            return;
+        }
+        // CraftBukkit end
         this.level.gameEvent(this.source, GameEvent.EXPLODE, new Vec3D(this.x, this.y, this.z));
         Set<BlockPosition> set = Sets.newHashSet();
         boolean flag = true;
@@ -211,7 +226,39 @@
                         double d12 = (double) getSeenPercent(vec3d, entity);
                         double d13 = (1.0D - d7) * d12;
 
-                        entity.hurt(this.getDamageSource(), (float) ((int) ((d13 * d13 + d13) / 2.0D * 7.0D * (double) f2 + 1.0D)));
+                        // CraftBukkit start
+
+                        // Special case ender dragon only give knockback if no damage is cancelled
+                        // Thinks to note:
+                        // - Setting a velocity to a ComplexEntityPart is ignored (and therefore not needed)
+                        // - Damaging ComplexEntityPart while forward the damage to EntityEnderDragon
+                        // - Damaging EntityEnderDragon does nothing
+                        // - EntityEnderDragon hitbock always covers the other parts and is therefore always present
+                        if (entity instanceof EntityComplexPart) {
+                            continue;
+                        }
+
+                        CraftEventFactory.entityDamage = source;
+                        entity.lastDamageCancelled = false;
+
+                        if (entity instanceof EntityEnderDragon) {
+                            for (EntityComplexPart entityComplexPart : ((EntityEnderDragon) entity).subEntities) {
+                                // Calculate damage separately for each EntityComplexPart
+                                double d7part;
+                                if (list.contains(entityComplexPart) && (d7part = Math.sqrt(entityComplexPart.distanceToSqr(vec3d)) / f2) <= 1.0D) {
+                                    double d13part = (1.0D - d7part) * getSeenPercent(vec3d, entityComplexPart);
+                                    entityComplexPart.hurt(this.getDamageSource(), (float) ((int) ((d13part * d13part + d13part) / 2.0D * 7.0D * (double) f2 + 1.0D)));
+                                }
+                            }
+                        } else {
+                            entity.hurt(this.getDamageSource(), (float) ((int) ((d13 * d13 + d13) / 2.0D * 7.0D * (double) f2 + 1.0D)));
+                        }
+
+                        CraftEventFactory.entityDamage = null;
+                        if (entity.lastDamageCancelled) { // SPIGOT-5339, SPIGOT-6252, SPIGOT-6777: Skip entity if damage event was cancelled
+                            continue;
+                        }
+                        // CraftBukkit end
                         double d14 = d13;
 
                         if (entity instanceof EntityLiving) {
@@ -254,6 +301,51 @@
 
             SystemUtils.shuffle(this.toBlow, this.level.random);
             ObjectListIterator objectlistiterator = this.toBlow.iterator();
+            // CraftBukkit start
+            org.bukkit.World bworld = this.level.getWorld();
+            org.bukkit.entity.Entity explode = this.source == null ? null : this.source.getBukkitEntity();
+            Location location = new Location(bworld, this.x, this.y, this.z);
+
+            List<org.bukkit.block.Block> blockList = new ObjectArrayList<>();
+            for (int i1 = this.toBlow.size() - 1; i1 >= 0; i1--) {
+                BlockPosition cpos = (BlockPosition) this.toBlow.get(i1);
+                org.bukkit.block.Block bblock = bworld.getBlockAt(cpos.getX(), cpos.getY(), cpos.getZ());
+                if (!bblock.getType().isAir()) {
+                    blockList.add(bblock);
+                }
+            }
+
+            boolean cancelled;
+            List<org.bukkit.block.Block> bukkitBlocks;
+            float yield;
+
+            if (explode != null) {
+                EntityExplodeEvent event = new EntityExplodeEvent(explode, location, blockList, this.blockInteraction == Explosion.Effect.DESTROY_WITH_DECAY ? 1.0F / this.radius : 1.0F);
+                this.level.getCraftServer().getPluginManager().callEvent(event);
+                cancelled = event.isCancelled();
+                bukkitBlocks = event.blockList();
+                yield = event.getYield();
+            } else {
+                BlockExplodeEvent event = new BlockExplodeEvent(location.getBlock(), blockList, this.blockInteraction == Explosion.Effect.DESTROY_WITH_DECAY ? 1.0F / this.radius : 1.0F);
+                this.level.getCraftServer().getPluginManager().callEvent(event);
+                cancelled = event.isCancelled();
+                bukkitBlocks = event.blockList();
+                yield = event.getYield();
+            }
+
+            this.toBlow.clear();
+
+            for (org.bukkit.block.Block bblock : bukkitBlocks) {
+                BlockPosition coords = new BlockPosition(bblock.getX(), bblock.getY(), bblock.getZ());
+                toBlow.add(coords);
+            }
+
+            if (cancelled) {
+                this.wasCanceled = true;
+                return;
+            }
+            // CraftBukkit end
+            objectlistiterator = this.toBlow.iterator();
 
             while (objectlistiterator.hasNext()) {
                 BlockPosition blockposition = (BlockPosition) objectlistiterator.next();
@@ -272,8 +364,8 @@
                             TileEntity tileentity = iblockdata.hasBlockEntity() ? this.level.getBlockEntity(blockposition) : null;
                             LootTableInfo.Builder loottableinfo_builder = (new LootTableInfo.Builder(worldserver)).withRandom(this.level.random).withParameter(LootContextParameters.ORIGIN, Vec3D.atCenterOf(blockposition)).withParameter(LootContextParameters.TOOL, ItemStack.EMPTY).withOptionalParameter(LootContextParameters.BLOCK_ENTITY, tileentity).withOptionalParameter(LootContextParameters.THIS_ENTITY, this.source);
 
-                            if (this.blockInteraction == Explosion.Effect.DESTROY_WITH_DECAY) {
-                                loottableinfo_builder.withParameter(LootContextParameters.EXPLOSION_RADIUS, this.radius);
+                            if (yield < 1.0F) { // CraftBukkit - add yield
+                                loottableinfo_builder.withParameter(LootContextParameters.EXPLOSION_RADIUS, 1.0F / yield); // CraftBukkit - add yield
                             }
 
                             iblockdata.spawnAfterBreak(worldserver, blockposition, ItemStack.EMPTY, flag2);
@@ -305,7 +397,11 @@
                 BlockPosition blockposition2 = (BlockPosition) objectlistiterator1.next();
 
                 if (this.random.nextInt(3) == 0 && this.level.getBlockState(blockposition2).isAir() && this.level.getBlockState(blockposition2.below()).isSolidRender(this.level, blockposition2.below())) {
-                    this.level.setBlockAndUpdate(blockposition2, BlockFireAbstract.getState(this.level, blockposition2));
+                    // CraftBukkit start - Ignition by explosion
+                    if (!org.bukkit.craftbukkit.event.CraftEventFactory.callBlockIgniteEvent(this.level, blockposition2.getX(), blockposition2.getY(), blockposition2.getZ(), this).isCancelled()) {
+                        this.level.setBlockAndUpdate(blockposition2, BlockFireAbstract.getState(this.level, blockposition2));
+                    }
+                    // CraftBukkit end
                 }
             }
         }
@@ -317,6 +413,7 @@
     }
 
     private static void addBlockDrops(ObjectArrayList<Pair<ItemStack, BlockPosition>> objectarraylist, ItemStack itemstack, BlockPosition blockposition) {
+        if (itemstack.isEmpty()) return; // CraftBukkit - SPIGOT-5425
         int i = objectarraylist.size();
 
         for (int j = 0; j < i; ++j) {