Modify signature of plugin reset callback.

The `reset` function is called inside `mj_resetData`, before any physics forwarding call has been made. It is therefore an error to read anything from mjData at this stage.

The only valid operation on mjData during `reset` is for a plugin to write into its own state variable slots and data struct. We modify the function signature to only provide access to these.

PiperOrigin-RevId: 495032492
Change-Id: Ic6d2967d2571a9083cbca1ba239ca70a8a51f474

doc/includes/references.h

@@ -1179,7 +1179,7 @@ struct mjpPlugin_ {
   void (*copy)(mjData* dest, const mjModel* m, const mjData* src, int instance);
 
   // called when an mjData is being reset (required)
-  void (*reset)(const mjModel* m, mjData* d, int instance);
+  void (*reset)(const mjModel* m, double* plugin_state, void* plugin_data, int instance);
 
   // called when the plugin needs to update its outputs (required)
   void (*compute)(const mjModel* m, mjData* d, int instance, int capability_bit);

include/mujoco/mjplugin.h

@@ -52,7 +52,7 @@ struct mjpPlugin_ {
   void (*copy)(mjData* dest, const mjModel* m, const mjData* src, int instance);
 
   // called when an mjData is being reset (required)
-  void (*reset)(const mjModel* m, mjData* d, int instance);
+  void (*reset)(const mjModel* m, double* plugin_state, void* plugin_data, int instance);
 
   // called when the plugin needs to update its outputs (required)
   void (*compute)(const mjModel* m, mjData* d, int instance, int capability_bit);

src/engine/engine_io.c

@@ -1149,7 +1149,8 @@ static void _resetData(const mjModel* m, mjData* d, unsigned char debug_value) {
     d->plugin[i] = m->plugin[i];
     const mjpPlugin* plugin = mjp_getPluginAtSlot(m->plugin[i]);
     if (plugin->reset) {
-      plugin->reset(m, d, i);
+      plugin->reset(m, &d->plugin_state[m->plugin_stateadr[i]],
+                    (void*)(d->plugin_data[i]), i);
     }
   }
 }

test/engine/engine_plugin_test.cc

@@ -224,8 +224,9 @@ int RegisterSensorPlugin() {
     TestSensor::DestroyCount()++;
   };
 
-  plugin.reset = +[](const mjModel* m, mjData* d, int instance) {
-    auto sensor = reinterpret_cast<TestSensor*>(d->plugin_data[instance]);
+  plugin.reset = +[](const mjModel* m, double* plugin_state, void* plugin_data,
+                     int instance) {
+    auto sensor = reinterpret_cast<TestSensor*>(plugin_data);
     sensor->Reset();
   };
   plugin.compute = +[](const mjModel* m, mjData* d, int instance, int type) {
@@ -266,8 +267,9 @@ int RegisterActuatorPlugin() {
     TestActuator::DestroyCount()++;
   };
 
-  plugin.reset = +[](const mjModel* m, mjData* d, int instance) {
-    auto actuator = reinterpret_cast<TestActuator*>(d->plugin_data[instance]);
+  plugin.reset = +[](const mjModel* m, double* plugin_state, void* plugin_data,
+                     int instance) {
+    auto actuator = reinterpret_cast<TestActuator*>(plugin_data);
     actuator->Reset();
   };
   plugin.compute = +[](const mjModel* m, mjData* d, int instance, int type) {
@@ -306,8 +308,9 @@ int RegisterPassivePlugin() {
     d->plugin_data[instance] = 0;
   };
 
-  plugin.reset = +[](const mjModel* m, mjData* d, int instance) {
-    auto passive = reinterpret_cast<TestPassive*>(d->plugin_data[instance]);
+  plugin.reset = +[](const mjModel* m, double* plugin_state, void* plugin_data,
+                     int instance) {
+    auto passive = reinterpret_cast<TestPassive*>(plugin_data);
     passive->Reset();
   };
   plugin.compute = +[](const mjModel* m, mjData* d, int instance, int type) {