Delete plugins when their corresponding objects are deleted, if their instance belonged the object.

Fixes #2061.

PiperOrigin-RevId: 676402701
Change-Id: Ia4807d57a3763e2100702b7e7ec96c300d0a9cfb

src/user/user_objects.cc

@@ -984,6 +984,10 @@ mjCBody::~mjCBody() {
   sites.clear();
   cameras.clear();
   lights.clear();
+
+  if (spec.plugin.active && spec.plugin.instance_name->empty()) {
+    model->DeleteElement(spec.plugin.instance);
+  }
 }
 
 
@@ -2107,6 +2111,14 @@ mjCGeom::mjCGeom(const mjCGeom& other) {
 
 
 
+mjCGeom::~mjCGeom() {
+  if (spec.plugin.active && spec.plugin.instance_name->empty()) {
+    model->DeleteElement(spec.plugin.instance);
+  }
+}
+
+
+
 mjCGeom& mjCGeom::operator=(const mjCGeom& other) {
   if (this != &other) {
     this->spec = other.spec;
@@ -5521,6 +5533,14 @@ mjCActuator::mjCActuator(const mjCActuator& other) {
 
 
 
+mjCActuator::~mjCActuator() {
+  if (spec.plugin.active && spec.plugin.instance_name->empty()) {
+    model->DeleteElement(spec.plugin.instance);
+  }
+}
+
+
+
 mjCActuator& mjCActuator::operator=(const mjCActuator& other) {
   if (this != &other) {
     this->spec = other.spec;
@@ -5875,6 +5895,14 @@ mjCSensor::mjCSensor(const mjCSensor& other) {
 
 
 
+mjCSensor::~mjCSensor() {
+  if (spec.plugin.active && spec.plugin.instance_name->empty()) {
+    model->DeleteElement(spec.plugin.instance);
+  }
+}
+
+
+
 mjCSensor& mjCSensor::operator=(const mjCSensor& other) {
   if (this != &other) {
     this->spec = other.spec;