PaperMC/paper-server/nms-patches/net/minecraft/world/entity/projectile/EntitySmallFireball.patch

--- a/net/minecraft/world/entity/projectile/EntitySmallFireball.java
+++ b/net/minecraft/world/entity/projectile/EntitySmallFireball.java
@@ -13,6 +13,8 @@
 import net.minecraft.world.phys.MovingObjectPositionBlock;
 import net.minecraft.world.phys.MovingObjectPositionEntity;
 
+import org.bukkit.event.entity.EntityCombustByEntityEvent; // CraftBukkit
+
 public class EntitySmallFireball extends EntityFireballFireball {
 
     public EntitySmallFireball(EntityTypes<? extends EntitySmallFireball> entitytypes, World world) {
@@ -21,6 +23,11 @@
 
     public EntitySmallFireball(World world, EntityLiving entityliving, double d0, double d1, double d2) {
         super(EntityTypes.SMALL_FIREBALL, entityliving, d0, d1, d2, world);
+        // CraftBukkit start
+        if (this.getOwner() != null && this.getOwner() instanceof EntityInsentient) {
+            isIncendiary = this.level.getGameRules().getBoolean(GameRules.RULE_MOBGRIEFING);
+        }
+        // CraftBukkit end
     }
 
     public EntitySmallFireball(World world, double d0, double d1, double d2, double d3, double d4, double d5) {
@@ -37,7 +44,14 @@
                 Entity entity1 = this.getOwner();
                 int i = entity.getRemainingFireTicks();
 
-                entity.setSecondsOnFire(5);
+                // CraftBukkit start - Entity damage by entity event + combust event
+                EntityCombustByEntityEvent event = new EntityCombustByEntityEvent((org.bukkit.entity.Projectile) this.getBukkitEntity(), entity.getBukkitEntity(), 5);
+                entity.level.getCraftServer().getPluginManager().callEvent(event);
+
+                if (!event.isCancelled()) {
+                    entity.setSecondsOnFire(event.getDuration(), false);
+                }
+                // CraftBukkit end
                 boolean flag = entity.hurt(DamageSource.fireball(this, entity1), 5.0F);
 
                 if (!flag) {
@@ -56,10 +70,10 @@
         if (!this.level.isClientSide) {
             Entity entity = this.getOwner();
 
-            if (!(entity instanceof EntityInsentient) || this.level.getGameRules().getBoolean(GameRules.RULE_MOBGRIEFING)) {
+            if (isIncendiary) { // CraftBukkit
                 BlockPosition blockposition = movingobjectpositionblock.getBlockPos().relative(movingobjectpositionblock.getDirection());
 
-                if (this.level.isEmptyBlock(blockposition)) {
+                if (this.level.isEmptyBlock(blockposition) && !org.bukkit.craftbukkit.event.CraftEventFactory.callBlockIgniteEvent(level, blockposition, this).isCancelled()) { // CraftBukkit
                     this.level.setBlockAndUpdate(blockposition, BlockFireAbstract.getState(this.level, blockposition));
                 }
             }