working

tools/java/BaseVehicleConstraintPatch.java

@@ -3,27 +3,34 @@ import java.nio.file.Path;
 import java.nio.file.Paths;
 import org.objectweb.asm.ClassReader;
 import org.objectweb.asm.ClassWriter;
+import org.objectweb.asm.Opcodes;
 import org.objectweb.asm.tree.AbstractInsnNode;
 import org.objectweb.asm.tree.ClassNode;
-import org.objectweb.asm.tree.InsnNode;
 import org.objectweb.asm.tree.InsnList;
+import org.objectweb.asm.tree.InsnNode;
 import org.objectweb.asm.tree.LdcInsnNode;
 import org.objectweb.asm.tree.MethodInsnNode;
 import org.objectweb.asm.tree.MethodNode;
-import org.objectweb.asm.Opcodes;
 
 /**
- * Patches zombie.vehicles.BaseVehicle so addPointConstraint() no longer force-breaks
- * both vehicles before creating a new constraint.
+ * Patches zombie.vehicles.BaseVehicle for Landtrain chain support:
+ * 1) remove forced breakConstraint() in addPointConstraint()
+ * 2) route constraintChanged() driver lookups through helper that handles chain middle vehicles
  */
 public final class BaseVehicleConstraintPatch {
     private static final String TARGET_NAME = "addPointConstraint";
+    private static final String CONSTRAINT_CHANGED_NAME = "constraintChanged";
     private static final String CLINIT_NAME = "<clinit>";
     private static final String VOID_NOARG_DESC = "()V";
     private static final String PATCH_LOG_LINE = "[Landtrain][BaseVehiclePatch] BaseVehicle override enabled";
     private static final String BREAK_DESC_OBJECT_BOOL = "(ZLjava/lang/Boolean;)V";
     private static final String BREAK_DESC_PRIMITIVE_BOOL = "(ZZ)V";
     private static final String BASE_VEHICLE_OWNER = "zombie/vehicles/BaseVehicle";
+    private static final String GET_DRIVER_DESC = "()Lzombie/characters/IsoGameCharacter;";
+    private static final String HELPER_OWNER = "zombie/vehicles/LandtrainConstraintAuthHelper";
+    private static final String HELPER_METHOD = "resolveConstraintDriver";
+    private static final String HELPER_DESC =
+            "(Lzombie/vehicles/BaseVehicle;)Lzombie/characters/IsoGameCharacter;";
 
     private BaseVehicleConstraintPatch() {
     }
@@ -43,12 +50,16 @@ public final class BaseVehicleConstraintPatch {
 
         int removedCalls = 0;
         int inspectedAddPointMethods = 0;
+        int patchedConstraintDriverCalls = 0;
+
         for (MethodNode method : classNode.methods) {
-            if (!TARGET_NAME.equals(method.name) || !isTargetAddPointConstraint(method.desc)) {
-                continue;
+            if (TARGET_NAME.equals(method.name) && isTargetAddPointConstraint(method.desc)) {
+                inspectedAddPointMethods++;
+                removedCalls += patchAddPointConstraint(method);
+            } else if (CONSTRAINT_CHANGED_NAME.equals(method.name)
+                    && VOID_NOARG_DESC.equals(method.desc)) {
+                patchedConstraintDriverCalls += patchConstraintChangedDriverCalls(method);
             }
-            inspectedAddPointMethods++;
-            removedCalls += patchAddPointConstraint(method);
         }
 
         if (removedCalls < 2) {
@@ -59,6 +70,11 @@ public final class BaseVehicleConstraintPatch {
                             + inspectedAddPointMethods
                             + ")");
         }
+        if (patchedConstraintDriverCalls < 1) {
+            throw new IllegalStateException(
+                    "Expected to patch at least 1 constraintChanged getDriver call, patched "
+                            + patchedConstraintDriverCalls);
+        }
         if (!ensureClassInitLog(classNode)) {
             throw new IllegalStateException("Failed to inject BaseVehicle class-init debug log");
         }
@@ -71,12 +87,12 @@ public final class BaseVehicleConstraintPatch {
         System.out.println(
                 "Patched BaseVehicle.class; removed breakConstraint calls: "
                         + removedCalls
+                        + ", constraint driver hooks: "
+                        + patchedConstraintDriverCalls
                         + ", class-init debug log: enabled");
     }
 
     private static boolean isTargetAddPointConstraint(String methodDesc) {
-        // We only want the 5-arg overload:
-        // (IsoPlayer, BaseVehicle, String, String, boolean|Boolean) -> void
         return "(Lzombie/characters/IsoPlayer;Lzombie/vehicles/BaseVehicle;Ljava/lang/String;Ljava/lang/String;Z)V"
                         .equals(methodDesc)
                 || "(Lzombie/characters/IsoPlayer;Lzombie/vehicles/BaseVehicle;Ljava/lang/String;Ljava/lang/String;Ljava/lang/Boolean;)V"
@@ -97,9 +113,8 @@ public final class BaseVehicleConstraintPatch {
                     node = next;
                     continue;
                 }
-                // Keep stack-map frames valid by preserving stack effect:
+
                 // breakConstraint(...) consumes objectref + 2 args and returns void.
-                // Replace invoke with POP2 + POP (consume 3 category-1 stack slots).
                 InsnList replacement = new InsnList();
                 replacement.add(new InsnNode(Opcodes.POP2));
                 replacement.add(new InsnNode(Opcodes.POP));
@@ -113,6 +128,36 @@ public final class BaseVehicleConstraintPatch {
         return patched;
     }
 
+    private static int patchConstraintChangedDriverCalls(MethodNode method) {
+        int patched = 0;
+        InsnList insns = method.instructions;
+        for (AbstractInsnNode node = insns.getFirst(); node != null; ) {
+            AbstractInsnNode next = node.getNext();
+            if (!(node instanceof MethodInsnNode call)) {
+                node = next;
+                continue;
+            }
+            if (!BASE_VEHICLE_OWNER.equals(call.owner)
+                    || !"getDriver".equals(call.name)
+                    || !GET_DRIVER_DESC.equals(call.desc)) {
+                node = next;
+                continue;
+            }
+
+            MethodInsnNode replacement =
+                    new MethodInsnNode(
+                            Opcodes.INVOKESTATIC,
+                            HELPER_OWNER,
+                            HELPER_METHOD,
+                            HELPER_DESC,
+                            false);
+            insns.set(call, replacement);
+            patched++;
+            node = next;
+        }
+        return patched;
+    }
+
     private static boolean ensureClassInitLog(ClassNode classNode) {
         MethodNode clinit = null;
         for (MethodNode method : classNode.methods) {

tools/java/LandtrainConstraintAuthHelper.java

@@ -0,0 +1,38 @@
+package zombie.vehicles;
+
+import zombie.characters.IsoGameCharacter;
+
+/**
+ * Resolves the effective driver for constraint auth in chained towing.
+ * For middle vehicles in a chain, prefer the front/lead driver's authority.
+ */
+public final class LandtrainConstraintAuthHelper {
+    private LandtrainConstraintAuthHelper() {
+    }
+
+    public static IsoGameCharacter resolveConstraintDriver(BaseVehicle vehicle) {
+        if (vehicle == null) {
+            return null;
+        }
+
+        IsoGameCharacter driver = vehicle.getDriver();
+        if (driver != null) {
+            return driver;
+        }
+
+        BaseVehicle front = vehicle.getVehicleTowedBy();
+        if (front != null) {
+            driver = front.getDriver();
+            if (driver != null) {
+                return driver;
+            }
+        }
+
+        BaseVehicle rear = vehicle.getVehicleTowing();
+        if (rear != null) {
+            return rear.getDriver();
+        }
+
+        return null;
+    }
+}