Return 0 on success from mjs_activatePlugin instead of using mju_error.

PiperOrigin-RevId: 684102823
Change-Id: I86b7702094ae886539e1dfb6294381952d507bc1

src/user/user_api.cc

@@ -206,14 +206,15 @@ void mjs_addSpec(mjSpec* s, mjSpec* child) {
 
 
 // activate plugin
-void mjs_activatePlugin(mjSpec* s, const char* name) {
+int mjs_activatePlugin(mjSpec* s, const char* name) {
   int plugin_slot = -1;
   const mjpPlugin* plugin = mjp_getPlugin(name, &plugin_slot);
   if (!plugin) {
-    mju_error("unknown plugin '%s'", name);
+    return -1;
   }
   mjCModel* model = static_cast<mjCModel*>(s->element);
   model->ActivatePlugin(plugin, plugin_slot);
+  return 0;
 }
 
 

src/user/user_api.h

@@ -63,8 +63,8 @@ MJAPI void mj_deleteSpec(mjSpec* s);
 // Add spec (model asset) to spec.
 MJAPI void mjs_addSpec(mjSpec* s, mjSpec* child);
 
-// Activate plugin.
-MJAPI void mjs_activatePlugin(mjSpec* s, const char* name);
+// Activate plugin, return 0 on success.
+MJAPI int mjs_activatePlugin(mjSpec* s, const char* name);
 
 
 //---------------------------------- Attachment ----------------------------------------------------

src/xml/xml_native_reader.cc

@@ -2890,7 +2890,9 @@ void mjXReader::Extension(XMLElement* section) {
     if (name == "plugin") {
       string plugin_name;
       ReadAttrTxt(elem, "plugin", plugin_name, /* required = */ true);
-      mjs_activatePlugin(spec, plugin_name.c_str());
+      if (mjs_activatePlugin(spec, plugin_name.c_str())) {
+        throw mjXError(elem, "plugin %s not found", plugin_name.c_str());
+      }
 
       XMLElement* child = FirstChildElement(elem);
       while (child) {