Add error handling to mj_recompile.

This CL adds error handling to the mj_recompile function. If the recompile fails, the function will return -1 and set the error message in the spec. The Python wrapper for mj_recompile will catch the error and raise a ValueError exception.

PiperOrigin-RevId: 666784579
Change-Id: I225eca1769ea839c782be3c03fc4ff1ea5885a48

src/user/user_api.cc

@@ -90,8 +90,8 @@ 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) {
+// recompile spec to model, preserving the state, return 0 on success
+[[nodiscard]] int mj_recompile(mjSpec* s, const mjVFS* vfs, mjModel* m, mjData* d) {
   mjCModel* modelC = static_cast<mjCModel*>(s->element);
   std::string state_name = "state";
   mjtNum time = 0;
@@ -99,13 +99,19 @@ void mj_recompile(mjSpec* s, const mjVFS* vfs, mjModel* m, mjData* d) {
     time = d->time;
     modelC->SaveState(state_name, d->qpos, d->qvel, d->act, d->ctrl, d->mocap_pos, d->mocap_quat);
   }
-  modelC->Compile(vfs, &m);
+  if (!modelC->Compile(vfs, &m)) {
+    if (d) {
+      mj_deleteData(d);
+    }
+    return -1;
+  };
   if (d) {
     modelC->MakeData(m, &d);
     modelC->RestoreState(state_name, m->qpos0, m->body_pos, m->body_quat, d->qpos, d->qvel,
                          d->act, d->ctrl, d->mocap_pos, d->mocap_quat);
     d->time = time;
   }
+  return 0;
 }
 
 

src/user/user_api.h

@@ -42,8 +42,8 @@ MJAPI mjSpec* mj_makeSpec(void);
 // Compile spec to model.
 MJAPI mjModel* mj_compile(mjSpec* s, const mjVFS* vfs);
 
-// Recompile spec to model preserving the current state.
-MJAPI void mj_recompile(mjSpec* s, const mjVFS* vfs, mjModel* m, mjData* d);
+// Recompile spec to model, preserving the state, return 0 on success.
+MJAPI int mj_recompile(mjSpec* s, const mjVFS* vfs, mjModel* m, mjData* d);
 
 // Copy spec.
 MJAPI mjSpec* mj_copySpec(const mjSpec* s);