From 09b0529f9a30a17ba7c288f1ea973300b8f4e84f Mon Sep 17 00:00:00 2001
From: Kyle Wood <demonwav@gmail.com>
Date: Sun, 23 Sep 2018 12:52:21 -0500
Subject: [PATCH] Enable experimental ASM support for Java 11 plugins

JEP 181 brings a new bytecode format for nest mates. ASM API 7 supports
this, but API 7 is still experimental. Attempting to load a Java 11
class that contains nest mates will cause an
UnsupportedOperationException, as API 6 can't handle them. This doesn't
really require any changes to the rest of the code, since this is just
related to ASM's visitor.

We want to use the stable API 6 for all other plugins, only using the
experimental API when required, so we check the class version first.

This should be removed as soon as ASM API 7 is stable.

diff --git a/pom.xml b/pom.xml
index 1e7d2b550..6d8b27e92 100644
--- a/pom.xml
+++ b/pom.xml
@@ -83,7 +83,7 @@
         <dependency>
             <groupId>org.ow2.asm</groupId>
             <artifactId>asm</artifactId>
-            <version>6.2</version>
+            <version>6.2.1</version>
             <scope>compile</scope>
         </dependency>
         <dependency>
diff --git a/src/main/java/org/bukkit/craftbukkit/util/Commodore.java b/src/main/java/org/bukkit/craftbukkit/util/Commodore.java
index d172a1aeb..7f2a73d6f 100644
--- a/src/main/java/org/bukkit/craftbukkit/util/Commodore.java
+++ b/src/main/java/org/bukkit/craftbukkit/util/Commodore.java
@@ -127,7 +127,16 @@ public class Commodore
         ClassReader cr = new ClassReader( b );
         ClassWriter cw = new ClassWriter( cr, 0 );
 
-        cr.accept( new ClassVisitor( Opcodes.ASM6, cw )
+        // Paper start - experimental support of Java 11
+        final int apiVersion;
+        if ( cr.readShort(6) == Opcodes.V11 ) {
+            apiVersion = Opcodes.ASM7_EXPERIMENTAL;
+        } else {
+            apiVersion = Opcodes.ASM6;
+        }
+
+        cr.accept( new ClassVisitor( apiVersion, cw )
+        // Paper end - experimental support of Java 11
         {
             @Override
             public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions)
-- 
2.19.0