Suppress structures in the spawn area too (#116)

src/main/java/world/bentobox/caveblock/CaveBlock.java

@@ -70,7 +70,8 @@ public void onEnable()
 
         // Register listeners
         this.registerListener(new CustomHeightLimitations(this));
-        this.registerListener(new StructureGenerationListener(this));
+        // StructureGenerationListener is registered earlier, in createWorlds(), so it is
+        // active before the first chunks (including the spawn area) are generated.
     }
 
 
@@ -138,6 +139,11 @@ public void allLoaded() {
     @Override
     public void createWorlds()
     {
+        // Register the structure listener before any world is created. createWorlds() runs
+        // before onEnable(), and generating a world also generates its spawn-area chunks, so a
+        // listener registered in onEnable() would miss those first structures (issue #116).
+        this.registerListener(new StructureGenerationListener(this));
+
         String worldName = this.settings.getWorldName().toLowerCase();
 
         if (this.getServer().getWorld(worldName) == null)

src/main/java/world/bentobox/caveblock/listeners/StructureGenerationListener.java

@@ -57,9 +57,8 @@ public StructureGenerationListener(CaveBlock addon) {
      */
     @EventHandler(priority = EventPriority.NORMAL, ignoreCancelled = true)
     public void onStructureSpawn(AsyncStructureSpawnEvent event) {
-        World world = event.getWorld();
         // Only the CaveBlock overworld uses vanilla structures; nether/end do not.
-        if (world.getEnvironment() != World.Environment.NORMAL || !addon.inWorld(world)) {
+        if (!isCaveOverworld(event.getWorld())) {
             return;
         }
         String structureKey = event.getStructure().getKey().getKey();
@@ -81,7 +80,7 @@ public void onStructureSpawn(AsyncStructureSpawnEvent event) {
      */
     @EventHandler(priority = EventPriority.NORMAL, ignoreCancelled = true)
     public void onStructuresLocate(StructuresLocateEvent event) {
-        if (!addon.inWorld(event.getWorld())) {
+        if (!isCaveOverworld(event.getWorld())) {
             return;
         }
         List<Structure> targets = event.getStructures();
@@ -100,6 +99,24 @@ public void onStructuresLocate(StructuresLocateEvent event) {
         }
     }
 
+    /**
+     * @param world a world
+     * @return {@code true} if {@code world} is the CaveBlock overworld.
+     *
+     * <p>Matches on the configured world name rather than {@link CaveBlock#inWorld(World)}
+     * because structures in the spawn area are generated during {@code createWorlds()},
+     * before the addon's island-world reference is assigned. At that point
+     * {@code inWorld()} would compare against a null world and fail, so the first
+     * structures would slip through (issue #116).</p>
+     */
+    private boolean isCaveOverworld(World world) {
+        if (world.getEnvironment() != World.Environment.NORMAL) {
+            return false;
+        }
+        String configuredName = addon.getSettings().getWorldName();
+        return configuredName != null && world.getName().equalsIgnoreCase(configuredName);
+    }
+
     /**
      * @param structureKey the vanilla structure key path, e.g. {@code ancient_city}
      * @return {@code true} if the config explicitly disables this structure

src/test/java/world/bentobox/caveblock/listeners/StructureGenerationListenerTest.java

@@ -50,7 +50,8 @@ public void setUp() {
         lenient().when(addon.getSettings()).thenReturn(settings);
         lenient().when(settings.getGenerateStructures())
                 .thenReturn(Map.of("ancient_city", false, "trial_chambers", false, "mineshaft", true));
-        lenient().when(addon.inWorld(world)).thenReturn(true);
+        lenient().when(settings.getWorldName()).thenReturn("caveblock_world");
+        lenient().when(world.getName()).thenReturn("caveblock_world");
         lenient().when(world.getEnvironment()).thenReturn(World.Environment.NORMAL);
         listener = new StructureGenerationListener(addon);
     }
@@ -92,7 +93,7 @@ void testUnlistedStructureGeneratesNormally() {
 
     @Test
     void testStructureOutsideCaveBlockWorldIsIgnored() {
-        when(addon.inWorld(world)).thenReturn(false);
+        when(world.getName()).thenReturn("some_other_world");
         AsyncStructureSpawnEvent e = event("ancient_city");
         listener.onStructureSpawn(e);
         verify(e, never()).setCancelled(true);
@@ -156,7 +157,7 @@ void testLocateAllEnabledIsUntouched() {
 
     @Test
     void testLocateOutsideCaveBlockWorldIsIgnored() {
-        when(addon.inWorld(world)).thenReturn(false);
+        when(world.getName()).thenReturn("some_other_world");
         StructuresLocateEvent e = locateEvent("trial_chambers");
         listener.onStructuresLocate(e);
         verify(e, never()).setCancelled(true);