Allow passing a null pointer in mj_recompile.

Fixes #1819.

PiperOrigin-RevId: 653242587
Change-Id: I36dbd6ed54abdf21abeb62cf41ee88f159008d01

src/user/user_api.cc

@@ -86,9 +86,14 @@ mjModel* mj_compile(mjSpec* s, const mjVFS* vfs) {
 // recompile spec into existing model and data while preserving the state
 void mj_recompile(mjSpec* s, const mjVFS* vfs, mjModel* m, mjData* d) {
   mjCModel* modelC = static_cast<mjCModel*>(s->element);
-  modelC->SaveState(d);
+  if (d) {
+    modelC->SaveState(d->qpos, d->qvel, d->act);
+  }
   modelC->Compile(vfs, &m);
-  modelC->RestoreState(m, &d);
+  if (d) {
+    modelC->MakeData(m, &d);
+    modelC->RestoreState(d->qpos, d->qvel, d->act);
+  }
 }
 
 

src/user/user_model.cc

@@ -2776,68 +2776,73 @@ void mjCModel::CopyObjects(mjModel* m) {
 
 
 // save the current state
-void mjCModel::SaveState(const mjData* d) {
+void mjCModel::SaveState(const mjtNum* qpos, const mjtNum* qvel, const mjtNum* act) {
   for (auto joint : joints_) {
     switch (joint->type) {
       case mjJNT_FREE:
-        mjuu_copyvec(joint->qpos, d->qpos + joint->qposadr_, 7);
-        mjuu_copyvec(joint->qvel, d->qvel + joint->dofadr_, 6);
+        if (qpos) mjuu_copyvec(joint->qpos, qpos + joint->qposadr_, 7);
+        if (qvel) mjuu_copyvec(joint->qvel, qvel + joint->dofadr_, 6);
         break;
       case mjJNT_BALL:
-        mjuu_copyvec(joint->qpos, d->qpos + joint->qposadr_, 4);
-        mjuu_copyvec(joint->qvel, d->qvel + joint->dofadr_, 3);
+        if (qpos) mjuu_copyvec(joint->qpos, qpos + joint->qposadr_, 4);
+        if (qvel) mjuu_copyvec(joint->qvel, qvel + joint->dofadr_, 3);
         break;
       case mjJNT_HINGE:
       case mjJNT_SLIDE:
-        mjuu_copyvec(joint->qpos, d->qpos + joint->qposadr_, 1);
-        mjuu_copyvec(joint->qvel, d->qvel + joint->dofadr_, 1);
+        if (qpos) mjuu_copyvec(joint->qpos, qpos + joint->qposadr_, 1);
+        if (qvel) mjuu_copyvec(joint->qvel, qvel + joint->dofadr_, 1);
         break;
     }
   }
 
   for (auto actuator : actuators_) {
-    if (actuator->actadr_ != -1) {
+    if (actuator->actadr_ != -1 && act) {
       actuator->act.assign(actuator->actnum_, 0);
-      mjuu_copyvec(actuator->act.data(), d->act + actuator->actadr_, actuator->actnum_);
+      mjuu_copyvec(actuator->act.data(), act + actuator->actadr_, actuator->actnum_);
     }
   }
 }
 
 
 
-// restore the previous state
-void mjCModel::RestoreState(const mjModel* m, mjData** dest) {
+// clear existing data
+void mjCModel::MakeData(const mjModel* m, mjData** dest) {
   mj_makeRawData(dest, m);
   mjData* d = *dest;
   if (d) {
     mj_initPlugin(m, d);
     mj_resetData(m, d);
   }
+}
 
+
+
+// restore the previous state
+void mjCModel::RestoreState(mjtNum* qpos, mjtNum* qvel, mjtNum* act) {
   for (auto joint : joints_) {
     if (!mjuu_defined(joint->qpos[0]) || !mjuu_defined(joint->qvel[0])) {
       continue;
     }
     switch (joint->type) {
       case mjJNT_FREE:
-        mjuu_copyvec(d->qpos + joint->qposadr_, joint->qpos, 7);
-        mjuu_copyvec(d->qvel + joint->dofadr_, joint->qvel, 6);
+        if (qpos) mjuu_copyvec(qpos + joint->qposadr_, joint->qpos, 7);
+        if (qvel) mjuu_copyvec(qvel + joint->dofadr_, joint->qvel, 6);
         break;
       case mjJNT_BALL:
-        mjuu_copyvec(d->qpos + joint->qposadr_, joint->qpos, 4);
-        mjuu_copyvec(d->qvel + joint->dofadr_, joint->qvel, 3);
+        if (qpos) mjuu_copyvec(qpos + joint->qposadr_, joint->qpos, 4);
+        if (qvel) mjuu_copyvec(qvel + joint->dofadr_, joint->qvel, 3);
         break;
       case mjJNT_HINGE:
       case mjJNT_SLIDE:
-        mjuu_copyvec(d->qpos + joint->qposadr_, joint->qpos, 1);
-        mjuu_copyvec(d->qvel + joint->dofadr_, joint->qvel, 1);
+        if (qpos) mjuu_copyvec(qpos + joint->qposadr_, joint->qpos, 1);
+        if (qvel) mjuu_copyvec(qvel + joint->dofadr_, joint->qvel, 1);
         break;
     }
   }
 
   for (auto actuator : actuators_) {
-    if (mjuu_defined(actuator->act[0])) {
-      mjuu_copyvec(d->act + actuator->actadr_, actuator->act.data(), actuator->actnum_);
+    if (mjuu_defined(actuator->act[0]) && act) {
+      mjuu_copyvec(act + actuator->actadr_, actuator->act.data(), actuator->actnum_);
     }
   }
 }

src/user/user_model.h

@@ -273,8 +273,9 @@ class mjCModel : public mjCModel_, private mjSpec {
                                          std::string_view name = "");
 
   // save/restore the current state
-  void SaveState(const mjData* d);
-  void RestoreState(const mjModel* m, mjData** dest);
+  void SaveState(const mjtNum* qpos, const mjtNum* qvel, const mjtNum* act);
+  void MakeData(const mjModel* m, mjData** dest);
+  void RestoreState(mjtNum* qpos, mjtNum* qvel, mjtNum* act);
 
   // map from default class name to default class pointer
   std::unordered_map<std::string, mjCDef*> def_map;

test/user/user_api_test.cc

@@ -863,8 +863,11 @@ TEST_F(MujocoTest, PreserveState) {
     EXPECT_EQ(data->act[i], d_expected->act[i]) << i;
   }
 
-  // destroy everything
+  // check that the function is callable with no data
   mj_deleteData(data);
+  mj_recompile(spec, 0, model, nullptr);
+
+  // destroy everything
   mj_deleteData(d_expected);
   mj_deleteSpec(spec);
   mj_deleteModel(model);