Clean up and clarify plugin loader logic.

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

@@ -22,7 +22,6 @@ import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
-import com.velocitypowered.api.event.EventManager;
 import com.velocitypowered.api.event.proxy.ProxyInitializeEvent;
 import com.velocitypowered.api.event.proxy.ProxyReloadEvent;
 import com.velocitypowered.api.event.proxy.ProxyShutdownEvent;

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

@@ -43,7 +43,6 @@ import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.HashSet;
 import java.util.IdentityHashMap;
 import java.util.LinkedHashMap;
@@ -58,7 +57,7 @@ public class VelocityPluginManager implements PluginManager {
 
   private static final Logger logger = LogManager.getLogger(VelocityPluginManager.class);
 
-  private final Map<String, PluginContainer> plugins = new LinkedHashMap<>();
+  private final Map<String, PluginContainer> pluginsById = new LinkedHashMap<>();
   private final Map<Object, PluginContainer> pluginInstances = new IdentityHashMap<>();
   private final VelocityServer server;
 
@@ -67,7 +66,7 @@ public class VelocityPluginManager implements PluginManager {
   }
 
   private void registerPlugin(PluginContainer plugin) {
-    plugins.put(plugin.getDescription().getId(), plugin);
+    pluginsById.put(plugin.getDescription().getId(), plugin);
     Optional<?> instance = plugin.getInstance();
     instance.ifPresent(o -> pluginInstances.put(o, plugin));
   }
@@ -90,7 +89,7 @@ public class VelocityPluginManager implements PluginManager {
         p -> p.toFile().isFile() && p.toString().endsWith(".jar"))) {
       for (Path path : stream) {
         try {
-          found.add(loader.loadPluginDescription(path));
+          found.add(loader.loadCandidate(path));
         } catch (Exception e) {
           logger.error("Unable to load plugin {}", path, e);
         }
@@ -119,7 +118,7 @@ public class VelocityPluginManager implements PluginManager {
       }
 
       try {
-        PluginDescription realPlugin = loader.loadPlugin(candidate);
+        PluginDescription realPlugin = loader.createPluginFromCandidate(candidate);
         VelocityPluginContainer container = new VelocityPluginContainer(realPlugin);
         pluginContainers.put(container, loader.createModule(container));
         loadedPluginsById.add(realPlugin.getId());
@@ -175,17 +174,17 @@ public class VelocityPluginManager implements PluginManager {
   @Override
   public Optional<PluginContainer> getPlugin(String id) {
     checkNotNull(id, "id");
-    return Optional.ofNullable(plugins.get(id));
+    return Optional.ofNullable(pluginsById.get(id));
   }
 
   @Override
   public Collection<PluginContainer> getPlugins() {
-    return Collections.unmodifiableCollection(plugins.values());
+    return Collections.unmodifiableCollection(pluginsById.values());
   }
 
   @Override
   public boolean isLoaded(String id) {
-    return plugins.containsKey(id);
+    return pluginsById.containsKey(id);
   }
 
   @Override

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

@@ -27,9 +27,23 @@ import java.nio.file.Path;
  */
 public interface PluginLoader {
 
-  PluginDescription loadPluginDescription(Path source) throws Exception;
+  /**
+   * Loads a candidate description from the given {@code source}.
+   *
+   * @param source the source to load the candidate from
+   * @return a plugin candidate description
+   * @throws Exception if anything goes wrong
+   */
+  PluginDescription loadCandidate(Path source) throws Exception;
 
-  PluginDescription loadPlugin(PluginDescription source) throws Exception;
+  /**
+   * Materializes a "real" plugin description from the given {@code candidate}.
+   *
+   * @param candidate the candidate to materialize
+   * @return a plugin description
+   * @throws Exception if anything goes wrong
+   */
+  PluginDescription createPluginFromCandidate(PluginDescription candidate) throws Exception;
 
   /**
    * Creates a {@link Module} for the provided {@link PluginContainer}

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

@@ -57,7 +57,7 @@ public class JavaPluginLoader implements PluginLoader {
   }
 
   @Override
-  public PluginDescription loadPluginDescription(Path source) throws Exception {
+  public PluginDescription loadCandidate(Path source) throws Exception {
     Optional<SerializedPluginDescription> serialized = getSerializedPluginInfo(source);
 
     if (!serialized.isPresent()) {
@@ -73,20 +73,20 @@ public class JavaPluginLoader implements PluginLoader {
   }
 
   @Override
-  public PluginDescription loadPlugin(PluginDescription source) throws Exception {
-    if (!(source instanceof JavaVelocityPluginDescriptionCandidate)) {
+  public PluginDescription createPluginFromCandidate(PluginDescription candidate) throws Exception {
+    if (!(candidate instanceof JavaVelocityPluginDescriptionCandidate)) {
       throw new IllegalArgumentException("Description provided isn't of the Java plugin loader");
     }
 
-    URL pluginJarUrl = source.getSource().get().toUri().toURL();
+    URL pluginJarUrl = candidate.getSource().get().toUri().toURL();
     PluginClassLoader loader = AccessController.doPrivileged(
         (PrivilegedAction<PluginClassLoader>) () -> new PluginClassLoader(new URL[]{pluginJarUrl}));
     loader.addToClassloaders();
 
-    JavaVelocityPluginDescriptionCandidate candidate =
-        (JavaVelocityPluginDescriptionCandidate) source;
-    Class mainClass = loader.loadClass(candidate.getMainClass());
-    return createDescription(candidate, mainClass);
+    JavaVelocityPluginDescriptionCandidate candidateInst =
+        (JavaVelocityPluginDescriptionCandidate) candidate;
+    Class mainClass = loader.loadClass(candidateInst.getMainClass());
+    return createDescription(candidateInst, mainClass);
   }
 
   @Override