Banish all use of Optionals from Velocity entirely

api/src/main/java/com/velocitypowered/api/plugin/PluginContainer.java

@@ -7,7 +7,7 @@
 
 package com.velocitypowered.api.plugin;
 
-import java.util.Optional;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * A wrapper around a plugin loaded by the proxy.
@@ -26,7 +26,7 @@ public interface PluginContainer {
    *
    * @return the instance if available
    */
-  default Optional<?> instance() {
-    return Optional.empty();
+  default @Nullable Object instance() {
+    return null;
   }
 }

config/checkstyle/checkstyle.xml

@@ -39,13 +39,9 @@
 
   <module name="TreeWalker">
     <module name="OuterTypeFilename"/>
-    <!-- <module name="IllegalTokenText">
-      <property name="tokens" value="STRING_LITERAL, CHAR_LITERAL"/>
-      <property name="format"
-        value="\\u00(09|0(a|A)|0(c|C)|0(d|D)|22|27|5(C|c))|\\(0(10|11|12|14|15|42|47)|134)"/>
-      <property name="message"
-        value="Consider using special escape sequence instead of octal value or Unicode escaped value."/>
-    </module> -->
+    <module name="IllegalImport">
+      <property name="illegalClasses" value="java.util.Optional, java.util.OptionalDouble, java.util.OptionalInt, java.util.OptionalLong"/>
+    </module>
     <module name="AvoidEscapedUnicodeCharacters">
       <property name="allowEscapesForControlCharacters" value="true"/>
       <property name="allowByTailComment" value="true"/>

proxy/src/main/java/com/velocitypowered/proxy/VelocityServer.java

@@ -78,7 +78,6 @@ import java.util.Collection;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Optional;
 import java.util.ResourceBundle;
 import java.util.UUID;
 import java.util.concurrent.CompletableFuture;
@@ -327,10 +326,10 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
 
     // Register the plugin main classes so that we can fire the proxy initialize event
     for (PluginContainer plugin : pluginManager.plugins()) {
-      Optional<?> instance = plugin.instance();
-      if (instance.isPresent()) {
+      Object instance = plugin.instance();
+      if (instance != null) {
         try {
-          eventManager.registerInternally(plugin, instance.get());
+          eventManager.registerInternally(plugin, instance);
         } catch (Exception e) {
           logger.error("Unable to register plugin listener for {}",
               MoreObjects.firstNonNull(plugin.description().name(), plugin.description().id()), e);

proxy/src/main/java/com/velocitypowered/proxy/command/builtin/ServerCommand.java

@@ -29,7 +29,6 @@ import com.velocitypowered.api.proxy.connection.ServerConnection;
 import com.velocitypowered.api.proxy.server.RegisteredServer;
 import com.velocitypowered.api.proxy.server.ServerInfo;
 import java.util.List;
-import java.util.Optional;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 import net.kyori.adventure.identity.Identity;
@@ -76,13 +75,16 @@ public class ServerCommand implements SimpleCommand {
   }
 
   private void outputServerInformation(Player executor) {
-    String currentServer = Optional.ofNullable(executor.connectedServer())
-        .map(ServerConnection::serverInfo)
-        .map(ServerInfo::name).orElse("<unknown>");
+    String currentServerName = "<unknown>";
+    ServerConnection connectedTo = executor.connectedServer();
+    if (connectedTo != null) {
+      currentServerName = connectedTo.serverInfo().name();
+    }
+
     executor.sendMessage(Identity.nil(), Component.translatable(
         "velocity.command.server-current-server",
         NamedTextColor.YELLOW,
-        Component.text(currentServer)));
+        Component.text(currentServerName)));
 
     List<RegisteredServer> servers = BuiltinCommandUtil.sortedServerList(server);
     if (servers.size() > MAX_SERVERS_TO_LIST) {
@@ -98,7 +100,7 @@ public class ServerCommand implements SimpleCommand {
         .append(Component.space());
     for (int i = 0; i < servers.size(); i++) {
       RegisteredServer rs = servers.get(i);
-      serverListBuilder.append(formatServerComponent(currentServer, rs));
+      serverListBuilder.append(formatServerComponent(currentServerName, rs));
       if (i != servers.size() - 1) {
         serverListBuilder.append(Component.text(", ", NamedTextColor.GRAY));
       }

proxy/src/main/java/com/velocitypowered/proxy/plugin/VelocityPluginManager.java

@@ -49,7 +49,6 @@ import java.util.IdentityHashMap;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Optional;
 import java.util.Set;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -69,8 +68,10 @@ public class VelocityPluginManager implements PluginManager {
 
   private void registerPlugin(PluginContainer plugin) {
     plugins.put(plugin.description().id(), plugin);
-    Optional<?> instance = plugin.instance();
-    instance.ifPresent(o -> pluginInstances.put(o, plugin));
+    Object instance = plugin.instance();
+    if (instance != null) {
+      pluginInstances.put(instance, plugin);
+    }
   }
 
   /**
@@ -198,10 +199,7 @@ public class VelocityPluginManager implements PluginManager {
       throw new IllegalArgumentException("plugin is not loaded");
     }
 
-    Optional<?> optInstance = optContainer.instance();
-    checkArgument(optInstance.isPresent(), "plugin has no instance");
-
-    ClassLoader pluginClassloader = optInstance.get().getClass().getClassLoader();
+    ClassLoader pluginClassloader = plugin.getClass().getClassLoader();
     if (pluginClassloader instanceof PluginClassLoader) {
       ((PluginClassLoader) pluginClassloader).addPath(path);
     } else {

proxy/src/main/java/com/velocitypowered/proxy/plugin/loader/VelocityPluginContainer.java

@@ -19,8 +19,8 @@ package com.velocitypowered.proxy.plugin.loader;
 
 import com.velocitypowered.api.plugin.PluginContainer;
 import com.velocitypowered.api.plugin.PluginDescription;
-import java.util.Optional;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 public class VelocityPluginContainer implements PluginContainer {
 
@@ -37,8 +37,8 @@ public class VelocityPluginContainer implements PluginContainer {
   }
 
   @Override
-  public Optional<?> instance() {
-    return Optional.ofNullable(instance);
+  public @Nullable Object instance() {
+    return instance;
   }
 
   public void setInstance(Object instance) {

proxy/src/main/java/com/velocitypowered/proxy/plugin/loader/java/JavaPluginLoader.java

@@ -41,10 +41,10 @@ import java.nio.file.Path;
 import java.security.AccessController;
 import java.security.PrivilegedAction;
 import java.util.HashSet;
-import java.util.Optional;
 import java.util.Set;
 import java.util.jar.JarEntry;
 import java.util.jar.JarInputStream;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 public class JavaPluginLoader implements PluginLoader {
 
@@ -56,18 +56,16 @@ public class JavaPluginLoader implements PluginLoader {
 
   @Override
   public PluginDescription loadPluginDescription(Path source) throws Exception {
-    Optional<SerializedPluginDescription> serialized = getSerializedPluginInfo(source);
-
-    if (serialized.isEmpty()) {
+    SerializedPluginDescription serialized = getSerializedPluginInfo(source);
+    if (serialized == null) {
       throw new InvalidPluginException("Did not find a valid velocity-plugin.json.");
     }
 
-    SerializedPluginDescription pd = serialized.get();
-    if (!SerializedPluginDescription.ID_PATTERN.matcher(pd.getId()).matches()) {
-      throw new InvalidPluginException("Plugin ID '" + pd.getId() + "' is invalid.");
+    if (!SerializedPluginDescription.ID_PATTERN.matcher(serialized.getId()).matches()) {
+      throw new InvalidPluginException("Plugin ID '" + serialized.getId() + "' is invalid.");
     }
 
-    return createCandidateDescription(pd, source);
+    return createCandidateDescription(serialized, source);
   }
 
   @Override
@@ -131,7 +129,7 @@ public class JavaPluginLoader implements PluginLoader {
     ((VelocityPluginContainer) container).setInstance(instance);
   }
 
-  private Optional<SerializedPluginDescription> getSerializedPluginInfo(Path source)
+  private @Nullable SerializedPluginDescription getSerializedPluginInfo(Path source)
       throws Exception {
     boolean foundBungeeBukkitPluginFile = false;
     try (JarInputStream in = new JarInputStream(
@@ -140,8 +138,8 @@ public class JavaPluginLoader implements PluginLoader {
       while ((entry = in.getNextJarEntry()) != null) {
         if (entry.getName().equals("velocity-plugin.json")) {
           try (Reader pluginInfoReader = new InputStreamReader(in, StandardCharsets.UTF_8)) {
-            return Optional.of(VelocityServer.GENERAL_GSON.fromJson(pluginInfoReader,
-                SerializedPluginDescription.class));
+            return VelocityServer.GENERAL_GSON.fromJson(pluginInfoReader,
+                SerializedPluginDescription.class);
           }
         }
 
@@ -156,7 +154,7 @@ public class JavaPluginLoader implements PluginLoader {
             + "plugins.");
       }
 
-      return Optional.empty();
+      return null;
     }
   }
 

proxy/src/test/java/com/velocitypowered/proxy/testutil/FakePluginManager.java

@@ -23,7 +23,6 @@ import com.velocitypowered.api.plugin.PluginDescription;
 import com.velocitypowered.api.plugin.PluginManager;
 import java.nio.file.Path;
 import java.util.Collection;
-import java.util.Optional;
 import org.checkerframework.checker.nullness.qual.NonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -89,8 +88,8 @@ public class FakePluginManager implements PluginManager {
     }
 
     @Override
-    public Optional<?> instance() {
-      return Optional.of(instance);
+    public Object instance() {
+      return instance;
     }
   }
 }