Copy plugins when attaching a model.

Before this CL, the same mjCPlugin objects were referenced by both models.

Fixes #2100.

PiperOrigin-RevId: 680579479
Change-Id: Ida3459f78f9fa4a942cea31b3d5d3e8da2832feb

src/user/user_model.cc

@@ -24,11 +24,11 @@
 #include <cstdlib>
 #include <cstring>
 #include <exception>
-#include <map>
 #include <mutex>
 #include <string>
 #include <string_view>
 #include <thread>
+#include <unordered_map>
 #include <vector>
 
 #include <mujoco/mjdata.h>
@@ -164,9 +164,6 @@ mjCModel::mjCModel() {
 
   // point to model from spec
   PointToLocal();
-
-  // this class allocated the plugins
-  plugin_owner = true;
 }
 
 
@@ -180,7 +177,6 @@ mjCModel::mjCModel(const mjCModel& other) {
 
 mjCModel& mjCModel::operator=(const mjCModel& other) {
   if (this != &other) {
-    plugin_owner = false;
     this->spec = other.spec;
     *static_cast<mjCModel_*>(this) = static_cast<const mjCModel_&>(other);
     *static_cast<mjSpec*>(this) = static_cast<const mjSpec&>(other);
@@ -302,6 +298,22 @@ void mjCModel::SaveDofOffsets() {
 
 
 
+template <class T>
+static void mapplugin(
+    const std::unordered_map<mjCPlugin*, mjCPlugin*>& plugin_map, std::vector<T*>& list) {
+  for (const auto& element : list) {
+      if (element->spec.plugin.element) {
+        mjCPlugin* plugin = static_cast<mjCPlugin*>(element->spec.plugin.element);
+        // the referenced plugin might already exist in the source model
+        if (plugin_map.find(plugin) != plugin_map.end()) {
+          element->spec.plugin.element = plugin_map.at(plugin);
+        }
+      }
+    }
+}
+
+
+
 mjCModel& mjCModel::operator+=(const mjCModel& other) {
   // create global lists
   mjCBody *world = bodies_[0];
@@ -323,6 +335,21 @@ mjCModel& mjCModel::operator+=(const mjCModel& other) {
     for (const auto& key : other.key_pending_) {
       key_pending_.push_back(key);
     }
+
+    // create new plugins and map them
+    std::unordered_map<mjCPlugin*, mjCPlugin*> plugin_map;
+    for (const auto& plugin : other.plugins_) {
+      plugins_.push_back(new mjCPlugin(*plugin));
+      plugin_map[plugin] = plugins_.back();
+    }
+    mapplugin(plugin_map, bodies_);
+    mapplugin(plugin_map, geoms_);
+    mapplugin(plugin_map, meshes_);
+    mapplugin(plugin_map, actuators_);
+    mapplugin(plugin_map, sensors_);
+    for (const auto& active_plugin : other.active_plugins_) {
+      active_plugins_.emplace_back(active_plugin);
+    }
   }
   CopyList(flexes_, other.flexes_);
   CopyList(pairs_, other.pairs_);
@@ -335,10 +362,6 @@ mjCModel& mjCModel::operator+=(const mjCModel& other) {
   CopyList(texts_, other.texts_);
   CopyList(tuples_, other.tuples_);
 
-  // plugins are global
-  plugins_ = other.plugins_;
-  active_plugins_ = other.active_plugins_;
-
   // restore to the original state
   if (!compiled) {
     ResetTreeLists();
@@ -613,10 +636,7 @@ mjCModel::~mjCModel() {
   for (int i=0; i<keys_.size(); i++) delete keys_[i];
   for (int i=0; i<defaults_.size(); i++) delete defaults_[i];
   for (int i=0; i<specs_.size(); i++) mj_deleteSpec(specs_[i]);
-
-  if (plugin_owner) {
-    for (int i=0; i<plugins_.size(); i++) delete plugins_[i];
-  }
+  for (int i=0; i<plugins_.size(); i++) delete plugins_[i];
 
   // clear sizes and pointer lists created in Compile
   Clear();

src/user/user_model.h

@@ -386,7 +386,6 @@ class mjCModel : public mjCModel_, private mjSpec {
 
   mjListKeyMap ids;   // map from object names to ids
   mjCError errInfo;   // last error info
-  bool plugin_owner;  // this class allocated the plugins
   std::vector<mjKeyInfo> key_pending_;  // attached keyframes
 };
 #endif  // MUJOCO_SRC_USER_USER_MODEL_H_

test/user/user_api_test.cc

@@ -216,6 +216,56 @@ TEST_F(PluginTest, DeletePlugin) {
   mj_deleteModel(newmodel);
 }
 
+TEST_F(PluginTest, AttachPlugin) {
+  static constexpr char xml_1[] = R"(
+    <mujoco model="MuJoCo Model">
+      <worldbody>
+        <body name="body"/>
+      </worldbody>
+    </mujoco>)";
+
+  static constexpr char xml_2[] = R"(
+    <mujoco model="MuJoCo Model">
+      <extension>
+        <plugin plugin="mujoco.pid">
+          <instance name="actuator-1">
+            <config key="ki" value="4.0"/>
+            <config key="slewmax" value="3.14159"/>
+          </instance>
+        </plugin>
+      </extension>
+      <worldbody>
+        <body name="body">
+          <joint name="joint"/>
+          <geom size="0.1"/>
+        </body>
+      </worldbody>
+      <actuator>
+        <plugin name="actuator-1" plugin="mujoco.pid" instance="actuator-1"
+                joint="joint" actdim="2"/>
+      </actuator>
+    </mujoco>)";
+
+  std::array<char, 1000> err;
+  mjSpec* spec_1 = mj_parseXMLString(xml_1, 0, err.data(), err.size());
+  ASSERT_THAT(spec_1, NotNull()) << err.data();
+  mjSpec* spec_2 = mj_parseXMLString(xml_2, 0, err.data(), err.size());
+  ASSERT_THAT(spec_2, NotNull()) << err.data();
+
+  mjsBody* body_1 = mjs_findBody(spec_1, "body");
+  EXPECT_THAT(body_1, NotNull());
+  mjsFrame* attachment_frame = mjs_addFrame(body_1, 0);
+  EXPECT_THAT(attachment_frame, NotNull());
+
+  mjs_attachBody(attachment_frame, mjs_findBody(spec_2, "body"), "child-", "");
+  mjModel* model = mj_compile(spec_1, nullptr);
+  EXPECT_THAT(model, NotNull());
+
+  mj_deleteModel(model);
+  mj_deleteSpec(spec_1);
+  mj_deleteSpec(spec_2);
+}
+
 TEST_F(MujocoTest, RecompileFails) {
   mjSpec* spec = mj_makeSpec();
   mjsBody* body = mjs_addBody(mjs_findBody(spec, "world"), 0);