Fix: Strip synthetic LVT entries after exporting. (#135)

They are useful for the dumped classes, but they have incorrect labels and as such they confuse IDEA's debugger.

src/main/java/org/spongepowered/asm/mixin/transformer/DefaultExtensions.java

@@ -30,6 +30,7 @@
 import org.spongepowered.asm.mixin.transformer.ext.extensions.ExtensionCheckClass;
 import org.spongepowered.asm.mixin.transformer.ext.extensions.ExtensionCheckInterfaces;
 import org.spongepowered.asm.mixin.transformer.ext.extensions.ExtensionClassExporter;
+import org.spongepowered.asm.mixin.transformer.ext.extensions.ExtensionLVTCleaner;
 import org.spongepowered.asm.service.ISyntheticClassInfo;
 import org.spongepowered.asm.util.IConsumer;
 
@@ -54,6 +55,7 @@ public void accept(ISyntheticClassInfo item) {
         extensions.add(new InnerClassGenerator(registryDelegate, nestHostCoprocessor));
 
         extensions.add(new ExtensionClassExporter(environment));
+        extensions.add(new ExtensionLVTCleaner());
         extensions.add(new ExtensionCheckClass());
         extensions.add(new ExtensionCheckInterfaces());
     }

src/main/java/org/spongepowered/asm/mixin/transformer/ext/extensions/ExtensionLVTCleaner.java

@@ -0,0 +1,85 @@
+/*
+ * This file is part of Mixin, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) SpongePowered <https://www.spongepowered.org>
+ * Copyright (c) contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package org.spongepowered.asm.mixin.transformer.ext.extensions;
+
+import org.objectweb.asm.tree.ClassNode;
+import org.objectweb.asm.tree.LocalVariableNode;
+import org.objectweb.asm.tree.MethodNode;
+import org.spongepowered.asm.mixin.MixinEnvironment;
+import org.spongepowered.asm.mixin.transformer.ext.IExtension;
+import org.spongepowered.asm.mixin.transformer.ext.ITargetClassContext;
+import org.spongepowered.asm.util.Locals;
+
+import java.util.Iterator;
+
+/**
+ * Strips synthetic local variables from the LVT after exporting to avoid debuggers becoming confused by them.
+ */
+public class ExtensionLVTCleaner implements IExtension {
+
+    /* (non-Javadoc)
+     * @see org.spongepowered.asm.mixin.transformer.ext.IExtension#checkActive(
+     *      org.spongepowered.asm.mixin.MixinEnvironment)
+     */
+    @Override
+    public boolean checkActive(MixinEnvironment environment) {
+        return true;
+    }
+
+    /* (non-Javadoc)
+     * @see org.spongepowered.asm.mixin.transformer.IMixinTransformerModule
+     *     #preApply(org.spongepowered.asm.mixin.transformer.TargetClassContext)
+     */
+    @Override
+    public void preApply(ITargetClassContext context) {
+    }
+
+    /* (non-Javadoc)
+     * @see org.spongepowered.asm.mixin.transformer.IMixinTransformerModule
+     *    #postApply(org.spongepowered.asm.mixin.transformer.TargetClassContext)
+     */
+    @Override
+    public void postApply(ITargetClassContext context) {
+    }
+
+    /* (non-Javadoc)
+     * @see org.spongepowered.asm.mixin.transformer.ext.IExtension
+     *      #export(org.spongepowered.asm.mixin.MixinEnvironment,
+     *      java.lang.String, boolean, org.objectweb.asm.tree.ClassNode)
+     */
+    @Override
+    public void export(MixinEnvironment env, String name, boolean force, ClassNode classNode) {
+        for (MethodNode methodNode : classNode.methods) {
+            if (methodNode.localVariables != null) {
+                for (Iterator<LocalVariableNode> it = methodNode.localVariables.iterator(); it.hasNext(); ) {
+                    if (it.next() instanceof Locals.SyntheticLocalVariableNode) {
+                        it.remove();
+                    }
+                }
+            }
+        }
+    }
+
+}