Landtrain!!!!

tools/java/BaseVehicleConstraintPatch.java

@@ -0,0 +1,105 @@
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassWriter;
+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.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.
+ */
+public final class BaseVehicleConstraintPatch {
+    private static final String TARGET_NAME = "addPointConstraint";
+    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 BaseVehicleConstraintPatch() {
+    }
+
+    public static void main(String[] args) throws Exception {
+        if (args.length != 2) {
+            System.err.println("Usage: BaseVehicleConstraintPatch <input BaseVehicle.class> <output BaseVehicle.class>");
+            System.exit(2);
+        }
+
+        Path input = Paths.get(args[0]);
+        Path output = Paths.get(args[1]);
+        byte[] original = Files.readAllBytes(input);
+
+        ClassNode classNode = new ClassNode();
+        new ClassReader(original).accept(classNode, 0);
+
+        int removedCalls = 0;
+        int inspectedAddPointMethods = 0;
+        for (MethodNode method : classNode.methods) {
+            if (!TARGET_NAME.equals(method.name) || !isTargetAddPointConstraint(method.desc)) {
+                continue;
+            }
+            inspectedAddPointMethods++;
+            removedCalls += patchAddPointConstraint(method);
+        }
+
+        if (removedCalls < 2) {
+            throw new IllegalStateException(
+                    "Expected to remove 2 breakConstraint calls, removed "
+                            + removedCalls
+                            + " (inspected addPoint methods: "
+                            + inspectedAddPointMethods
+                            + ")");
+        }
+
+        ClassWriter writer = new ClassWriter(0);
+        classNode.accept(writer);
+
+        Files.createDirectories(output.getParent());
+        Files.write(output, writer.toByteArray());
+        System.out.println("Patched BaseVehicle.class; removed breakConstraint calls: " + removedCalls);
+    }
+
+    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"
+                        .equals(methodDesc);
+    }
+
+    private static int patchAddPointConstraint(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
+                    && BASE_VEHICLE_OWNER.equals(call.owner)
+                    && "breakConstraint".equals(call.name)) {
+                if (!(BREAK_DESC_OBJECT_BOOL.equals(call.desc)
+                        || BREAK_DESC_PRIMITIVE_BOOL.equals(call.desc))) {
+                    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));
+                insns.insert(node, replacement);
+                insns.remove(node);
+                patched++;
+            }
+            node = next;
+        }
+
+        return patched;
+    }
+}

tools/patch-game-basevehicle.ps1

@@ -0,0 +1,80 @@
+param(
+    [string]$GameRoot = "D:\SteamLibrary\steamapps\common\ProjectZomboid"
+)
+
+$ErrorActionPreference = "Stop"
+
+$repoRoot = Split-Path -Parent $PSScriptRoot
+$toolsDir = Join-Path $repoRoot ".tools"
+$classPatchDir = Join-Path $toolsDir "classpatch"
+$buildDir = Join-Path $toolsDir "patcher-build"
+
+New-Item -ItemType Directory -Force -Path $toolsDir | Out-Null
+New-Item -ItemType Directory -Force -Path $classPatchDir | Out-Null
+New-Item -ItemType Directory -Force -Path $buildDir | Out-Null
+
+$javaExe = Join-Path $GameRoot "jre64\bin\java.exe"
+$gameJar = Join-Path $GameRoot "projectzomboid.jar"
+if (-not (Test-Path $javaExe)) { throw "java.exe not found at $javaExe" }
+if (-not (Test-Path $gameJar)) { throw "projectzomboid.jar not found at $gameJar" }
+
+$ecjJar = Join-Path $toolsDir "ecj.jar"
+$asmJar = Join-Path $toolsDir "asm.jar"
+$asmTreeJar = Join-Path $toolsDir "asm-tree.jar"
+
+if (-not (Test-Path $ecjJar)) {
+    Invoke-WebRequest -Uri "https://repo1.maven.org/maven2/org/eclipse/jdt/ecj/3.38.0/ecj-3.38.0.jar" -OutFile $ecjJar
+}
+if (-not (Test-Path $asmJar)) {
+    Invoke-WebRequest -Uri "https://repo1.maven.org/maven2/org/ow2/asm/asm/9.9/asm-9.9.jar" -OutFile $asmJar
+}
+if (-not (Test-Path $asmTreeJar)) {
+    Invoke-WebRequest -Uri "https://repo1.maven.org/maven2/org/ow2/asm/asm-tree/9.9/asm-tree-9.9.jar" -OutFile $asmTreeJar
+}
+
+$patcherSource = Join-Path $PSScriptRoot "java\BaseVehicleConstraintPatch.java"
+if (-not (Test-Path $patcherSource)) { throw "Missing patcher source: $patcherSource" }
+
+& $javaExe -jar $ecjJar -17 -cp "$asmJar;$asmTreeJar" -d $buildDir $patcherSource
+if ($LASTEXITCODE -ne 0) { throw "Failed to compile BaseVehicleConstraintPatch.java" }
+
+$inputClass = Join-Path $classPatchDir "BaseVehicle.original.class"
+$patchedClass = Join-Path $classPatchDir "BaseVehicle.patched.class"
+
+Add-Type -AssemblyName System.IO.Compression.FileSystem
+$zip = [System.IO.Compression.ZipFile]::OpenRead($gameJar)
+try {
+    $entry = $zip.GetEntry("zombie/vehicles/BaseVehicle.class")
+    if ($null -eq $entry) { throw "zombie/vehicles/BaseVehicle.class not found in $gameJar" }
+
+    $entryStream = $entry.Open()
+    $fileStream = [System.IO.File]::Create($inputClass)
+    try {
+        $entryStream.CopyTo($fileStream)
+    } finally {
+        $fileStream.Close()
+        $entryStream.Close()
+    }
+} finally {
+    $zip.Dispose()
+}
+
+& $javaExe -cp "$buildDir;$asmJar;$asmTreeJar" BaseVehicleConstraintPatch $inputClass $patchedClass
+if ($LASTEXITCODE -ne 0) { throw "BaseVehicle class patch failed" }
+
+$targetDir = Join-Path $GameRoot "zombie\vehicles"
+$targetClass = Join-Path $targetDir "BaseVehicle.class"
+$backupClass = "$targetClass.landtrain.original"
+
+New-Item -ItemType Directory -Force -Path $targetDir | Out-Null
+if (-not (Test-Path $backupClass)) {
+    if (Test-Path $targetClass) {
+        Copy-Item $targetClass $backupClass -Force
+    } else {
+        Copy-Item $inputClass $backupClass -Force
+    }
+}
+
+Copy-Item $patchedClass $targetClass -Force
+Write-Output "Patched BaseVehicle.class deployed to $targetClass"
+Write-Output "Backup stored at $backupClass"

tools/restore-game-basevehicle.ps1

@@ -0,0 +1,18 @@
+param(
+    [string]$GameRoot = "D:\SteamLibrary\steamapps\common\ProjectZomboid"
+)
+
+$ErrorActionPreference = "Stop"
+
+$targetClass = Join-Path $GameRoot "zombie\vehicles\BaseVehicle.class"
+$backupClass = "$targetClass.landtrain.original"
+
+if (Test-Path $backupClass) {
+    Copy-Item $backupClass $targetClass -Force
+    Write-Output "Restored BaseVehicle.class from $backupClass"
+} elseif (Test-Path $targetClass) {
+    Remove-Item $targetClass -Force
+    Write-Output "Removed override class at $targetClass (game will use class from projectzomboid.jar)"
+} else {
+    Write-Output "No override or backup found. Nothing to restore."
+}