So, I'm currently running into a major issue where I can't open a world in my IDE. The crash happens once the world has been loaded up, and the client world screen is about to launch. When this happens, mouseClicked event handler reports:

Caused by: java.lang.NoSuchMethodError: io.netty.util.internal.ReflectionUtil.trySetAccessible(Ljava/lang/reflect/AccessibleObject;Z)Ljava/lang/Throwable;

I've had to reinstall netty, as files such as these sometimes just disappears, with no known cause. The version I installed was netty-all:4.1.25.Final. Since then I've also used :

gradlew --stop
gradlew clean

Note that I haven't had these issues before this, so it has nothing to do with forge version.

Edited June 5, 20214 yr by Pingun114
Minor info

Specifically, like I mentioned before, things like io.netty.util and net.minecraftforge.x.eventbus will sometimes disappear when I start up the IDE again, so I downloaded Netty and imported if as an external library. Now, I've since last checked, and the missing function does exist. As for the stacktrace, while I doubt it will help in this case, here:

-- Head --
Thread: Render thread
Stacktrace:
	at io.netty.channel.nio.NioEventLoop$5.run(NioEventLoop.java:219) ~[netty-all-4.1.25.Final.jar:4.1.25.Final] {}
	at java.security.AccessController.doPrivileged(Native Method) ~[?:1.8.0_161] {}
	at io.netty.channel.nio.NioEventLoop.openSelector(NioEventLoop.java:212) ~[netty-all-4.1.25.Final.jar:4.1.25.Final] {}
	at io.netty.channel.nio.NioEventLoop.<init>(NioEventLoop.java:151) ~[netty-all-4.1.25.Final.jar:4.1.25.Final] {}
	at io.netty.channel.nio.NioEventLoopGroup.newChild(NioEventLoopGroup.java:127) ~[netty-all-4.1.25.Final.jar:4.1.25.Final] {}
	at io.netty.channel.nio.NioEventLoopGroup.newChild(NioEventLoopGroup.java:36) ~[netty-all-4.1.25.Final.jar:4.1.25.Final] {}
	at io.netty.util.concurrent.MultithreadEventExecutorGroup.<init>(MultithreadEventExecutorGroup.java:84) ~[patchy-1.1.jar:?] {}
	at io.netty.util.concurrent.MultithreadEventExecutorGroup.<init>(MultithreadEventExecutorGroup.java:58) ~[patchy-1.1.jar:?] {}
	at io.netty.util.concurrent.MultithreadEventExecutorGroup.<init>(MultithreadEventExecutorGroup.java:47) ~[patchy-1.1.jar:?] {}
	at io.netty.channel.MultithreadEventLoopGroup.<init>(MultithreadEventLoopGroup.java:59) ~[netty-all-4.1.25.Final.jar:4.1.25.Final] {}
	at io.netty.channel.nio.NioEventLoopGroup.<init>(NioEventLoopGroup.java:77) ~[netty-all-4.1.25.Final.jar:4.1.25.Final] {}
	at io.netty.channel.nio.NioEventLoopGroup.<init>(NioEventLoopGroup.java:72) ~[netty-all-4.1.25.Final.jar:4.1.25.Final] {}
	at io.netty.channel.nio.NioEventLoopGroup.<init>(NioEventLoopGroup.java:59) ~[netty-all-4.1.25.Final.jar:4.1.25.Final] {}
	at net.minecraft.network.NetworkSystem.lambda$static$0(NetworkSystem.java:46) ~[?:?] {re:classloading}
	at net.minecraft.util.LazyValue.getValue(LazyValue.java:16) ~[?:?] {re:classloading}
	at net.minecraft.network.NetworkSystem.addLocalEndpoint(NetworkSystem.java:115) ~[?:?] {re:classloading}
	at net.minecraft.client.Minecraft.loadWorld(Minecraft.java:1832) ~[?:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.Minecraft.loadWorld(Minecraft.java:1728) ~[?:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.screen.WorldSelectionList$Entry.func_214443_e(WorldSelectionList.java:364) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.screen.WorldSelectionList$Entry.func_214438_a(WorldSelectionList.java:273) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.screen.WorldSelectionList$Entry.mouseClicked(WorldSelectionList.java:225) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.widget.list.AbstractList.mouseClicked(AbstractList.java:309) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.INestedGuiEventHandler.mouseClicked(INestedGuiEventHandler.java:31) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.MouseHelper.lambda$mouseButtonCallback$0(MouseHelper.java:92) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
-- Affected screen --
Details:
	Screen name: net.minecraft.client.gui.screen.WorldSelectionScreen
Stacktrace:
	at net.minecraft.client.gui.screen.Screen.wrapScreenError(Screen.java:427) ~[forge-1.16.4-35.1.36_mapped_snapshot_20201028-1.16.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.MouseHelper.mouseButtonCallback(MouseHelper.java:90) ~[forge-1.16.4-35.1.36_mapped_snapshot_20201028-1.16.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.MouseHelper.lambda$null$4(MouseHelper.java:185) ~[forge-1.16.4-35.1.36_mapped_snapshot_20201028-1.16.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.util.concurrent.ThreadTaskExecutor.execute(ThreadTaskExecutor.java:86) ~[forge-1.16.4-35.1.36_mapped_snapshot_20201028-1.16.3-recomp.jar:?] {re:classloading,pl:accesstransformer:B,re:mixin,pl:accesstransformer:B}
	at net.minecraft.client.MouseHelper.lambda$registerCallbacks$5(MouseHelper.java:184) ~[forge-1.16.4-35.1.36_mapped_snapshot_20201028-1.16.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at org.lwjgl.glfw.GLFWMouseButtonCallbackI.callback(GLFWMouseButtonCallbackI.java:36) ~[lwjgl-glfw-3.2.2.jar:build 10] {}
	at org.lwjgl.system.JNI.invokeV(Native Method) ~[lwjgl-3.2.2.jar:build 10] {}
	at org.lwjgl.glfw.GLFW.glfwWaitEventsTimeout(GLFW.java:3174) ~[lwjgl-glfw-3.2.2.jar:build 10] {}
	at com.mojang.blaze3d.systems.RenderSystem.limitDisplayFPS(RenderSystem.java:112) ~[forge-1.16.4-35.1.36_mapped_snapshot_20201028-1.16.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:1025) ~[forge-1.16.4-35.1.36_mapped_snapshot_20201028-1.16.3-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.Minecraft.run(Minecraft.java:612) ~[forge-1.16.4-35.1.36_mapped_snapshot_20201028-1.16.3-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.main.Main.main(Main.java:184) ~[forge-1.16.4-35.1.36_mapped_snapshot_20201028-1.16.3-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_161] {}
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_161] {}
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_161] {}
	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_161] {}
	at net.minecraftforge.userdev.FMLUserdevClientLaunchProvider.lambda$launchService$0(FMLUserdevClientLaunchProvider.java:52) ~[forge-1.16.4-35.1.36_mapped_snapshot_20201028-1.16.3-recomp.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-8.0.6.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) [modlauncher-8.0.6.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) [modlauncher-8.0.6.jar:?] {}
	at cpw.mods.modlauncher.Launcher.run(Launcher.java:82) [modlauncher-8.0.6.jar:?] {}
	at cpw.mods.modlauncher.Launcher.main(Launcher.java:66) [modlauncher-8.0.6.jar:?] {}
	at net.minecraftforge.userdev.LaunchTesting.main(LaunchTesting.java:105) [forge-1.16.4-35.1.36_mapped_snapshot_20201028-1.16.3-recomp.jar:?] {}

 

Well, I removed it, completely cleared my workspace, and updated to latest stable forge version. Can't really check currently since there's been a lot of mapping changes, to my code. Actually, is there somewhere I can see the new mapping changes? It would not only be useful for this, but in the future, too.