client: add plugin sideloading

This supports sideloading plugins out of the sideloaded-plugins
directory when run in developer mode

runelite-client/src/main/java/net/runelite/client/RuneLite.java

@@ -323,6 +323,7 @@ public class RuneLite
 		// Load the plugins, but does not start them yet.
 		// This will initialize configuration
 		pluginManager.loadCorePlugins();
+		pluginManager.loadSideLoadPlugins();
 		externalPluginManager.loadExternalPlugins();
 
 		SplashScreen.stage(.70, null, "Finalizing configuration");

runelite-client/src/main/java/net/runelite/client/plugins/PluginClassLoader.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2016-2017, Adam <Adam@sigterm.info>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package net.runelite.client.plugins;
+
+import java.io.File;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLClassLoader;
+
+class PluginClassLoader extends URLClassLoader
+{
+	private final ClassLoader parent;
+
+	PluginClassLoader(File plugin, ClassLoader parent) throws MalformedURLException
+	{
+		// null parent classloader, or else class path scanning includes everything from the main class loader
+		super(new URL[]{plugin.toURI().toURL()}, null);
+
+		this.parent = parent;
+	}
+
+	@Override
+	public Class<?> loadClass(String name) throws ClassNotFoundException
+	{
+		try
+		{
+			return super.loadClass(name);
+		}
+		catch (ClassNotFoundException ex)
+		{
+			// fall back to main class loader
+			return parent.loadClass(name);
+		}
+	}
+}

runelite-client/src/main/java/net/runelite/client/plugins/PluginManager.java

@@ -37,6 +37,7 @@ import com.google.inject.CreationException;
 import com.google.inject.Injector;
 import com.google.inject.Key;
 import com.google.inject.Module;
+import java.io.File;
 import java.io.IOException;
 import java.lang.invoke.CallSite;
 import java.lang.invoke.LambdaMetafactory;
@@ -87,6 +88,7 @@ public class PluginManager
 	 * Base package where the core plugins are
 	 */
 	private static final String PLUGIN_PACKAGE = "net.runelite.client.plugins";
+	private static final File SIDELOADED_PLUGINS = new File(RuneLite.RUNELITE_DIR, "sideloaded-plugins");
 
 	private final boolean developerMode;
 	private final boolean safeMode;
@@ -275,6 +277,45 @@ public class PluginManager
 			SplashScreen.stage(.60, .70, null, "Loading Plugins", loaded, total, false));
 	}
 
+	public void loadSideLoadPlugins()
+	{
+		if (!developerMode)
+		{
+			return;
+		}
+
+		File[] files = SIDELOADED_PLUGINS.listFiles();
+		if (files == null)
+		{
+			return;
+		}
+
+		for (File f : files)
+		{
+			if (f.getName().endsWith(".jar"))
+			{
+				log.info("Side-loading plugin {}", f);
+
+				try
+				{
+					ClassLoader classLoader = new PluginClassLoader(f, getClass().getClassLoader());
+
+					List<Class<?>> plugins = ClassPath.from(classLoader)
+						.getAllClasses()
+						.stream()
+						.map(ClassInfo::load)
+						.collect(Collectors.toList());
+
+					loadPlugins(plugins, null);
+				}
+				catch (PluginInstantiationException | IOException ex)
+				{
+					log.error("error sideloading plugin", ex);
+				}
+			}
+		}
+	}
+
 	public List<Plugin> loadPlugins(List<Class<?>> plugins, BiConsumer<Integer, Integer> onPluginLoaded) throws PluginInstantiationException
 	{
 		MutableGraph<Class<? extends Plugin>> graph = GraphBuilder