Add context action for clearing variable metadata on methods

Man, fuck Kotlin.

// "it" variable on stack, cast to iterable then stored
218: checkcast     #600 // class java/lang/Iterable
221: astore        11
223: nop
// "it" variable starts here
224: iconst_0
225: istore        12
// "it" variable first used here
227: aload         11
229: astore        13
231: new           #988 // class java/util/ArrayList
234: dup

Bunch of junk between the "start" and actual write, which makes it really confusing when parsing from ASM's model.

This is a workaround. A proper fix should target upstream JASM - https://github.com/jumanji144/Jasm/blob/c5a2c9050312497f53378f8c6a397ec3d3f02ef6/jasm-composition-jvm/src/main/java/me/darknet/assembler/printer/JvmMethodPrinter.java#L92

Author: Col-E

recaf-core/src/main/java/software/coley/recaf/util/visitors/MethodVariableRemovingVisitor.java

@@ -0,0 +1,67 @@
+package software.coley.recaf.util.visitors;
+
+import jakarta.annotation.Nullable;
+import org.objectweb.asm.AnnotationVisitor;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.Label;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.TypePath;
+import software.coley.recaf.RecafConstants;
+import software.coley.recaf.util.AccessFlag;
+
+/**
+ * A visitor that removes method variables.
+ * Generally useful for fixing kotlin classes since their variable tables are all sorts of wrong.
+ *
+ * @author Matt Coley
+ */
+public class MethodVariableRemovingVisitor extends ClassVisitor {
+	private final MemberPredicate predicate;
+
+	/**
+	 * @param cv
+	 * 		Parent visitor.
+	 * @param predicate
+	 * 		Predicate to match which methods will be cleaned, or {@code null} to clean all methods.
+	 */
+	public MethodVariableRemovingVisitor(@Nullable ClassVisitor cv, @Nullable MemberPredicate predicate) {
+		super(RecafConstants.getAsmVersion(), cv);
+
+		this.predicate = predicate;
+	}
+
+	@Override
+	public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
+		MethodVisitor mv = super.visitMethod(access, name, descriptor, signature, exceptions);
+
+		// Skip if already no code.
+		if (AccessFlag.isAbstract(access) || AccessFlag.isNative(access))
+			return mv;
+
+		// Only clean matched methods.
+		if (predicate == null || predicate.matchMethod(access, name, descriptor, signature, exceptions))
+			return new VarRemovingVisitor(mv);
+
+		return mv;
+	}
+
+	/**
+	 * Method visitor that removes any local variable debug info.
+	 */
+	public static class VarRemovingVisitor extends MethodVisitor {
+		public VarRemovingVisitor(@Nullable MethodVisitor mv) {
+			super(RecafConstants.getAsmVersion(), mv);
+		}
+
+		@Override
+		public void visitLocalVariable(String name, String descriptor, String signature, Label start, Label end, int index) {
+			// skip
+		}
+
+		@Override
+		public AnnotationVisitor visitLocalVariableAnnotation(int typeRef, TypePath typePath, Label[] start, Label[] end, int[] index, String descriptor, boolean visible) {
+			// skip
+			return null;
+		}
+	}
+}

recaf-ui/src/main/java/software/coley/recaf/services/cell/context/BasicMethodContextMenuProviderFactory.java

@@ -81,6 +81,7 @@ public ContextMenuProvider getMethodContextMenuProvider(@Nonnull ContextSource s
 					JvmClassInfo declaringJvmClass = declaringClass.asJvmClass();
 
 					edit.item("menu.edit.copy", COPY_FILE, () -> actions.copyMember(workspace, resource, jvmBundle, declaringJvmClass, method));
+					edit.item("menu.edit.removevars", CIRCLE_DASH, () -> actions.removeMethodVariables(workspace, resource, jvmBundle, declaringJvmClass, List.of(method)));
 					if (!method.getName().equals("<init>")) // The conditions for optimally no-op'ing a constructor are a bit tricky, we'll just skip those for now.
 						edit.item("menu.edit.noop", CIRCLE_DASH, () -> actions.makeMethodsNoop(workspace, resource, jvmBundle, declaringJvmClass, List.of(method)));
 					edit.item("menu.edit.delete", TRASH_CAN, () -> actions.deleteClassMethods(workspace, resource, jvmBundle, declaringJvmClass, List.of(method)));

recaf-ui/src/main/java/software/coley/recaf/services/navigation/Actions.java

@@ -103,6 +103,7 @@
 import software.coley.recaf.util.visitors.MethodAnnotationRemovingVisitor;
 import software.coley.recaf.util.visitors.MethodNoopingVisitor;
 import software.coley.recaf.util.visitors.MethodPredicate;
+import software.coley.recaf.util.visitors.MethodVariableRemovingVisitor;
 import software.coley.recaf.workspace.PathExportingManager;
 import software.coley.recaf.workspace.model.BasicWorkspace;
 import software.coley.recaf.workspace.model.Workspace;
@@ -2098,6 +2099,34 @@ public void makeMethodsNoop(@Nonnull Workspace workspace,
 				.build());
 	}
 
+	/**
+	 * Removes variable debug info in the given methods.
+	 *
+	 * @param workspace
+	 * 		Containing workspace.
+	 * @param resource
+	 * 		Containing resource.
+	 * @param bundle
+	 * 		Containing bundle.
+	 * @param declaringClass
+	 * 		Class declaring the methods.
+	 * @param methods
+	 * 		Methods to clean.
+	 */
+	public void removeMethodVariables(@Nonnull Workspace workspace,
+	                            @Nonnull WorkspaceResource resource,
+	                            @Nonnull JvmClassBundle bundle,
+	                            @Nonnull JvmClassInfo declaringClass,
+	                            @Nonnull Collection<MethodMember> methods) {
+		ClassReader reader = declaringClass.getClassReader();
+		ClassWriter writer = new ClassWriter(reader, 0);
+		MethodVariableRemovingVisitor visitor = new MethodVariableRemovingVisitor(writer, MethodPredicate.of(methods));
+		reader.accept(visitor, declaringClass.getClassReaderFlags());
+		bundle.put(declaringClass.toJvmClassBuilder()
+				.adaptFrom(writer.toByteArray())
+				.build());
+	}
+
 	/**
 	 * @param bundle
 	 * 		Containing bundle.

recaf-ui/src/main/resources/translations/en_US.lang

@@ -48,6 +48,7 @@ menu.edit.remove=Remove
 menu.edit.copy=Copy
 menu.edit.delete=Delete
 menu.edit.noop=Make no-op
+menu.edit.removevars=Prune variable info
 menu.edit.changeversion=Change class versions
 menu.edit.changeversion.up=Upgrade
 menu.edit.changeversion.down=Downgrade