Print more useful debug message when a LinkageError is thrown due to bad SLF4J classloading

This is a longstanding issue, mostly caused by plugins with bad Maven shade configurations.

https://github.com/lucko/LuckPerms/issues?q=slf4j

bukkit/src/main/java/me/lucko/luckperms/bukkit/LPBukkitBootstrap.java

@@ -39,6 +39,7 @@ import org.bukkit.Server;
 import org.bukkit.command.ConsoleCommandSender;
 import org.bukkit.entity.Player;
 import org.bukkit.plugin.java.JavaPlugin;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 import java.io.InputStream;
 import java.nio.file.Path;
@@ -268,6 +269,14 @@ public class LPBukkitBootstrap extends JavaPlugin implements LuckPermsBootstrap
         return player != null && player.isOnline();
     }
 
+    @Override
+    public @Nullable String identifyClassLoader(ClassLoader classLoader) {
+        if (classLoader instanceof org.bukkit.plugin.java.PluginClassLoader) {
+            return ((org.bukkit.plugin.java.PluginClassLoader) classLoader).getPlugin().getName();
+        }
+        return null;
+    }
+
     private static boolean checkIncompatibleVersion() {
         try {
             Class.forName("com.google.gson.JsonElement");

bungee/src/main/java/me/lucko/luckperms/bungee/LPBungeeBootstrap.java

@@ -36,6 +36,9 @@ import me.lucko.luckperms.common.plugin.scheduler.SchedulerAdapter;
 import net.luckperms.api.platform.Platform;
 import net.md_5.bungee.api.connection.ProxiedPlayer;
 import net.md_5.bungee.api.plugin.Plugin;
+import net.md_5.bungee.api.plugin.PluginDescription;
+
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 import java.io.InputStream;
 import java.nio.file.Path;
@@ -260,6 +263,16 @@ public class LPBungeeBootstrap extends Plugin implements LuckPermsBootstrap {
         return getProxy().getPlayer(uniqueId) != null;
     }
 
+    @Override
+    public @Nullable String identifyClassLoader(ClassLoader classLoader) throws Exception {
+        Class<?> pluginClassLoader = Class.forName("net.md_5.bungee.api.plugin.PluginClassloader");
+        if (pluginClassLoader.isInstance(classLoader)) {
+            PluginDescription desc = (PluginDescription) pluginClassLoader.getDeclaredField("desc").get(classLoader);
+            return desc.getName();
+        }
+        return null;
+    }
+
     private static boolean checkIncompatibleVersion() {
         try {
             Class<?> aClass = Class.forName("com.google.gson.internal.bind.TreeTypeAdapter");

common/src/main/java/me/lucko/luckperms/common/plugin/bootstrap/LuckPermsBootstrap.java

@@ -214,4 +214,17 @@ public interface LuckPermsBootstrap {
      */
     boolean isPlayerOnline(UUID uniqueId);
 
+    /**
+     * Attempts to identify the plugin behind the given classloader.
+     *
+     * <p>Used for giving more helpful log messages when things break.</p>
+     *
+     * @param classLoader the classloader to identify
+     * @return the name of the classloader source
+     * @throws Exception anything
+     */
+    default @Nullable String identifyClassLoader(ClassLoader classLoader) throws Exception {
+        return null;
+    }
+
 }

common/src/main/java/me/lucko/luckperms/common/storage/implementation/sql/SqlStorage.java

@@ -147,7 +147,7 @@ public class SqlStorage implements StorageImplementation {
 
     @Override
     public void init() throws Exception {
-        this.connectionFactory.init();
+        this.connectionFactory.init(this.plugin);
 
         boolean tableExists;
         try (Connection c = this.connectionFactory.getConnection()) {

common/src/main/java/me/lucko/luckperms/common/storage/implementation/sql/connection/ConnectionFactory.java

@@ -25,6 +25,8 @@
 
 package me.lucko.luckperms.common.storage.implementation.sql.connection;
 
+import me.lucko.luckperms.common.plugin.LuckPermsPlugin;
+
 import java.sql.Connection;
 import java.sql.SQLException;
 import java.util.Collections;
@@ -35,7 +37,7 @@ public interface ConnectionFactory {
 
     String getImplementationName();
 
-    void init();
+    void init(LuckPermsPlugin plugin);
 
     void shutdown() throws Exception;
 

common/src/main/java/me/lucko/luckperms/common/storage/implementation/sql/connection/file/FlatfileConnectionFactory.java

@@ -25,6 +25,7 @@
 
 package me.lucko.luckperms.common.storage.implementation.sql.connection.file;
 
+import me.lucko.luckperms.common.plugin.LuckPermsPlugin;
 import me.lucko.luckperms.common.storage.implementation.sql.connection.ConnectionFactory;
 
 import java.io.IOException;
@@ -44,7 +45,7 @@ abstract class FlatfileConnectionFactory implements ConnectionFactory {
     }
 
     @Override
-    public void init() {
+    public void init(LuckPermsPlugin plugin) {
 
     }
 

common/src/main/java/me/lucko/luckperms/common/storage/implementation/sql/connection/hikari/HikariConnectionFactory.java

@@ -25,9 +25,12 @@
 
 package me.lucko.luckperms.common.storage.implementation.sql.connection.hikari;
 
+import com.google.common.collect.ImmutableList;
 import com.zaxxer.hikari.HikariConfig;
 import com.zaxxer.hikari.HikariDataSource;
 
+import me.lucko.luckperms.common.plugin.LuckPermsPlugin;
+import me.lucko.luckperms.common.plugin.logging.PluginLogger;
 import me.lucko.luckperms.common.storage.implementation.sql.connection.ConnectionFactory;
 import me.lucko.luckperms.common.storage.misc.StorageCredentials;
 
@@ -36,6 +39,7 @@ import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.HashMap;
 import java.util.LinkedHashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 
@@ -73,8 +77,17 @@ public abstract class HikariConnectionFactory implements ConnectionFactory {
     }
 
     @Override
-    public void init() {
+    public void init(LuckPermsPlugin plugin) {
-        HikariConfig config = new HikariConfig();
+        HikariConfig config;
+        try {
+            config = new HikariConfig();
+        } catch (LinkageError e) {
+            // dumb plugins seem to keep doing stupid stuff with shading of SLF4J and Log4J.
+            // detect this and print a more useful error message.
+            handleLinkageError(e, plugin);
+            throw e;
+        }
+
         config.setPoolName("luckperms-hikari");
 
         appendConfigurationInfo(config);
@@ -141,4 +154,38 @@ public abstract class HikariConnectionFactory implements ConnectionFactory {
         }
         return connection;
     }
+
+    private static void handleLinkageError(LinkageError linkageError, LuckPermsPlugin plugin) {
+        List<String> noteworthyClasses = ImmutableList.of(
+                "org.slf4j.LoggerFactory",
+                "org.slf4j.ILoggerFactory",
+                "org.apache.logging.slf4j.Log4jLoggerFactory",
+                "org.apache.logging.log4j.spi.LoggerContext",
+                "org.apache.logging.log4j.spi.AbstractLoggerAdapter",
+                "org.slf4j.impl.StaticLoggerBinder"
+        );
+
+        PluginLogger logger = plugin.getLogger();
+        logger.warn("A " + linkageError.getClass().getSimpleName() + " has occurred whilst initialising Hikari. This is likely due to classloading conflicts between other plugins.");
+        logger.warn("Please check for other plugins below (and try loading LuckPerms without them installed) before reporting the issue.");
+
+        for (String className : noteworthyClasses) {
+            Class<?> clazz;
+            try {
+                clazz = Class.forName(className);
+            } catch (Exception ex) {
+                continue;
+            }
+
+            ClassLoader loader = clazz.getClassLoader();
+            String loaderName;
+            try {
+                loaderName = plugin.getBootstrap().identifyClassLoader(loader) + " (" + loader.toString() + ")";
+            } catch (Exception e) {
+                loaderName = loader.toString();
+            }
+
+            logger.warn("Class " + className + " has been loaded by: " + loaderName);
+        }
+    }
 }