Change advancement form mechanics to match Java behaviour, fix NPE

core/src/main/java/org/geysermc/geyser/command/defaults/AdvancementsCommand.java

@@ -42,6 +42,6 @@ public AdvancementsCommand(String name, String description, String permission) {
     @Override
     public void execute(CommandContext<GeyserCommandSource> context) {
         GeyserSession session = Objects.requireNonNull(context.sender().connection());
-        session.getAdvancementsCache().buildAndShowMenuForm();
+        session.getAdvancementsCache().buildAndShowForm();
     }
 }

core/src/main/java/org/geysermc/geyser/session/cache/AdvancementsCache.java

@@ -28,7 +28,6 @@
 import org.geysermc.mcprotocollib.protocol.data.game.advancement.Advancement;
 import org.geysermc.mcprotocollib.protocol.packet.ingame.serverbound.inventory.ServerboundSeenAdvancementsPacket;
 import lombok.Getter;
-import lombok.Setter;
 import org.geysermc.cumulus.form.SimpleForm;
 import org.geysermc.geyser.level.GeyserAdvancement;
 import org.geysermc.geyser.session.GeyserSession;
@@ -41,6 +40,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 
 public class AdvancementsCache {
     /**
@@ -58,15 +58,39 @@ public class AdvancementsCache {
     /**
      * Stores player's chosen advancement's ID and title for use in form creators.
      */
-    @Setter
     private String currentAdvancementCategoryId = null;
 
+    /**
+     * Stores if the player is currently viewing advancements.
+     */
+    private boolean formOpen = false;
+
     private final GeyserSession session;
 
     public AdvancementsCache(GeyserSession session) {
         this.session = session;
     }
 
+    public void setCurrentAdvancementCategoryId(String categoryId) {
+        if (!Objects.equals(currentAdvancementCategoryId, categoryId)) {
+            // Only open and show list form if we're going to a different category
+            currentAdvancementCategoryId = categoryId;
+            if (formOpen) {
+                session.closeForm();
+                buildAndShowForm();
+                formOpen = true;
+            }
+        }
+    }
+
+    public void buildAndShowForm() {
+        if (currentAdvancementCategoryId == null) {
+            buildAndShowMenuForm();
+        } else {
+            buildAndShowListForm();
+        }
+    }
+
     /**
      * Build and send a form with all advancement categories
      */
@@ -88,9 +112,11 @@ public void buildAndShowMenuForm() {
             builder.content("advancements.empty");
         }
 
-        builder.validResultHandler((response) -> {
+        builder.closedResultHandler(() -> {
+            formOpen = false;
+        }).validResultHandler((response) -> {
             String id = rootAdvancementIds.get(response.clickedButtonId());
-            if (!id.equals("")) {
+            if (!id.isEmpty()) {
                 // Send a packet indicating that we are opening this particular advancement window
                 ServerboundSeenAdvancementsPacket packet = new ServerboundSeenAdvancementsPacket(id);
                 session.sendDownstreamGamePacket(packet);
@@ -99,6 +125,7 @@ public void buildAndShowMenuForm() {
             }
         });
 
+        formOpen = true;
         session.sendForm(builder);
     }
 
@@ -133,6 +160,9 @@ public void buildAndShowListForm() {
 
         builder.closedResultHandler(() -> {
             // Indicate that we have closed the current advancement tab
+            // Don't set currentAdvancementCategoryId to null here, so that when the advancements form is shown again (buildAndShowForm),
+            // the tab that was last open is opened again, which matches Java behaviour
+            formOpen = false;
             session.sendDownstreamGamePacket(new ServerboundSeenAdvancementsPacket());
 
         }).validResultHandler((response) -> {
@@ -142,6 +172,7 @@ public void buildAndShowListForm() {
             } else {
                 buildAndShowMenuForm();
                 // Indicate that we have closed the current advancement tab
+                currentAdvancementCategoryId = null;
                 session.sendDownstreamGamePacket(new ServerboundSeenAdvancementsPacket());
             }
         });
@@ -206,6 +237,7 @@ public void buildAndShowInfoForm(GeyserAdvancement advancement) {
                         .validResultHandler((response) -> buildAndShowListForm())
                         .closedResultHandler(() -> {
                             // Indicate that we have closed the current advancement tab
+                            formOpen = false;
                             session.sendDownstreamGamePacket(new ServerboundSeenAdvancementsPacket());
                         })
         );

core/src/main/java/org/geysermc/geyser/translator/protocol/java/JavaSelectAdvancementsTabTranslator.java

@@ -27,7 +27,6 @@
 
 import org.geysermc.mcprotocollib.protocol.packet.ingame.clientbound.ClientboundSelectAdvancementsTabPacket;
 import org.geysermc.geyser.session.GeyserSession;
-import org.geysermc.geyser.session.cache.AdvancementsCache;
 import org.geysermc.geyser.translator.protocol.PacketTranslator;
 import org.geysermc.geyser.translator.protocol.Translator;
 
@@ -39,8 +38,6 @@ public class JavaSelectAdvancementsTabTranslator extends PacketTranslator<Client
 
     @Override
     public void translate(GeyserSession session, ClientboundSelectAdvancementsTabPacket packet) {
-        AdvancementsCache advancementsCache = session.getAdvancementsCache();
-        advancementsCache.setCurrentAdvancementCategoryId(packet.getTabId());
-        advancementsCache.buildAndShowListForm();
+        session.getAdvancementsCache().setCurrentAdvancementCategoryId(packet.getTabId());
     }
 }