PaperMC/nms-patches/BlockStationary.patch

--- a/net/minecraft/server/BlockStationary.java
+++ b/net/minecraft/server/BlockStationary.java
@@ -2,6 +2,8 @@
 
 import java.util.Random;
 
+import org.bukkit.craftbukkit.event.CraftEventFactory;  // CraftBukkit
+
 public class BlockStationary extends BlockFluids {
 
     protected BlockStationary(Material material) {
@@ -41,6 +43,13 @@
 
                         if (block.material == Material.AIR) {
                             if (this.f(world, blockposition1)) {
+                                 // CraftBukkit start - Prevent lava putting something on fire
+                                if (world.getType(blockposition1) != Blocks.FIRE) {
+                                    if (CraftEventFactory.callBlockIgniteEvent(world, blockposition1.getX(), blockposition1.getY(), blockposition1.getZ(), blockposition.getX(), blockposition.getY(), blockposition.getZ()).isCancelled()) {
+                                        continue;
+                                    }
+                                }
+                                // CraftBukkit end
                                 world.setTypeUpdate(blockposition1, Blocks.FIRE.getBlockData());
                                 return;
                             }
@@ -53,6 +62,14 @@
                         BlockPosition blockposition2 = blockposition.a(random.nextInt(3) - 1, 0, random.nextInt(3) - 1);
 
                         if (world.isEmpty(blockposition2.up()) && this.m(world, blockposition2)) {
+                            // CraftBukkit start - Prevent lava putting something on fire
+                            BlockPosition up = blockposition2.up();
+                            if (world.getType(up) != Blocks.FIRE) {
+                                if (CraftEventFactory.callBlockIgniteEvent(world, up.getX(), up.getY(), up.getZ(), blockposition.getX(), blockposition.getY(), blockposition.getZ()).isCancelled()) {
+                                    continue;
+                                }
+                            }
+                            // CraftBukkit end
                             world.setTypeUpdate(blockposition2.up(), Blocks.FIRE.getBlockData());
                         }
                     }