Add missing default namespaces.

Fixes #2162.

PiperOrigin-RevId: 688575676
Change-Id: I6c43e33ebead68dece0f779e6f031e90a5e19096

src/user/user_objects.cc

@@ -696,7 +696,7 @@ void mjCBase::NameSpace(const mjCModel* m) {
   if (!name.empty()) {
     name = m->prefix + name + m->suffix;
   }
-  if (!classname.empty() && m != model) {
+  if (!classname.empty() && classname != "main" && m != model) {
     classname = m->prefix + classname + m->suffix;
   }
 }
@@ -1014,12 +1014,7 @@ void mjCBody::NameSpace(const mjCModel* m) {
 
 // apply prefix and suffix, propagate to all descendents or only to child bodies
 void mjCBody::NameSpace_(const mjCModel* m, bool propagate) {
-  if (!name.empty()) {
+  mjCBase::NameSpace(m);
-    name = m->prefix + name + m->suffix;
-  }
-  if (!classname.empty() && m != model) {
-    classname = m->prefix + classname + m->suffix;
-  }
   if (!plugin_instance_name.empty()) {
     plugin_instance_name = m->prefix + plugin_instance_name + m->suffix;
   }
@@ -2257,12 +2252,7 @@ void mjCGeom::CopyFromSpec() {
 
 
 void mjCGeom::NameSpace(const mjCModel* m) {
-  if (!name.empty()) {
+  mjCBase::NameSpace(m);
-    name = m->prefix + name + m->suffix;
-  }
-  if (!classname.empty() && m != model) {
-    classname = m->prefix + classname + m->suffix;
-  }
   if (!spec_material_.empty() && model != m) {
     spec_material_ = m->prefix + spec_material_ + m->suffix;
   }
@@ -3219,12 +3209,7 @@ void mjCCamera::PointToLocal() {
 
 
 void mjCCamera::NameSpace(const mjCModel* m) {
-  if (!name.empty()) {
+  mjCBase::NameSpace(m);
-    name = m->prefix + name + m->suffix;
-  }
-  if (!classname.empty() && m != model) {
-    classname = m->prefix + classname + m->suffix;
-  }
   if (!spec_targetbody_.empty()) {
     spec_targetbody_ = m->prefix + spec_targetbody_ + m->suffix;
   }
@@ -3370,12 +3355,7 @@ void mjCLight::PointToLocal() {
 
 
 void mjCLight::NameSpace(const mjCModel* m) {
-  if (!name.empty()) {
+  mjCBase::NameSpace(m);
-    name = m->prefix + name + m->suffix;
-  }
-  if (!classname.empty() && m != model) {
-    classname = m->prefix + classname + m->suffix;
-  }
   if (!spec_targetbody_.empty()) {
     spec_targetbody_ = m->prefix + spec_targetbody_ + m->suffix;
   }
@@ -4565,9 +4545,7 @@ void mjCMaterial::CopyFromSpec() {
 
 
 void mjCMaterial::NameSpace(const mjCModel* m) {
-  if (!name.empty()) {
+  mjCBase::NameSpace(m);
-    name = m->prefix + name + m->suffix;
-  }
   for (int i=0; i<mjNTEXROLE; i++) {
     if (!spec_textures_[i].empty() && model != m) {
       spec_textures_[i] = m->prefix + spec_textures_[i] + m->suffix;
@@ -4651,9 +4629,7 @@ void mjCPair::PointToLocal() {
 
 
 void mjCPair::NameSpace(const mjCModel* m) {
-  if (!name.empty()) {
+  mjCBase::NameSpace(m);
-    name = m->prefix + name + m->suffix;
-  }
   prefix = m->prefix;
   suffix = m->suffix;
 }
@@ -5009,9 +4985,7 @@ void mjCEquality::PointToLocal() {
 
 
 void mjCEquality::NameSpace(const mjCModel* m) {
-  if (!name.empty()) {
+  mjCBase::NameSpace(m);
-    name = m->prefix + name + m->suffix;
-  }
   spec_name1_ = m->prefix + spec_name1_ + m->suffix;
   spec_name2_ = m->prefix + spec_name2_ + m->suffix;
 }
@@ -5179,9 +5153,7 @@ void mjCTendon::PointToLocal() {
 
 
 void mjCTendon::NameSpace(const mjCModel* m) {
-  if (!name.empty()) {
+  mjCBase::NameSpace(m);
-    name = m->prefix + name + m->suffix;
-  }
   prefix = m->prefix;
   suffix = m->suffix;
 }
@@ -5699,9 +5671,7 @@ void mjCActuator::PointToLocal() {
 
 
 void mjCActuator::NameSpace(const mjCModel* m) {
-  if (!name.empty()) {
+  mjCBase::NameSpace(m);
-    name = m->prefix + name + m->suffix;
-  }
   if (!plugin_instance_name.empty()) {
     plugin_instance_name = m->prefix + plugin_instance_name + m->suffix;
   }

test/xml/xml_native_writer_test.cc

@@ -14,6 +14,7 @@
 
 // Tests for xml/xml_native_writer.cc.
 
+#include <memory>
 #if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
 #include <unistd.h>
 #endif
@@ -1476,5 +1477,51 @@ TEST_F(DecompilerTest, VeryLargeNumbers) {
   mj_deleteModel(model);
 }
 
+TEST_F(XMLWriterTest, ExpandAttach) {
+  static constexpr char xml_parent[] = R"(
+  <mujoco>
+    <asset>
+      <model name="b" file="b.xml" />
+    </asset>
+
+    <worldbody>
+      <attach model="b" body="b" prefix="b" />
+    </worldbody>
+  </mujoco>
+  )";
+
+  static constexpr char xml_child[] = R"(
+  <mujoco>
+    <default>
+      <default class="b"/>
+    </default>
+
+    <worldbody>
+      <body name="b">
+        <geom type="box" size="0.1 0.1 0.1"/>
+        <joint name="b"/>
+      </body>
+    </worldbody>
+
+    <actuator>
+      <position joint="b" class="b"/>
+    </actuator>
+  </mujoco>
+  )";
+
+  auto vfs = std::make_unique<mjVFS>();
+  mj_defaultVFS(vfs.get());
+  mj_addBufferVFS(vfs.get(), "b.xml", xml_child, sizeof(xml_child));
+
+  std::array<char, 1024> er;
+  mjModel* m = LoadModelFromString(xml_parent, er.data(), er.size(), vfs.get());
+  ASSERT_THAT(m, NotNull()) << er.data();
+
+  std::string saved_xml = SaveAndReadXml(m);
+  EXPECT_THAT(saved_xml, HasSubstr("class=\"bb\""));
+  mj_deleteModel(m);
+  mj_deleteVFS(vfs.get());
+}
+
 }  // namespace
 }  // namespace mujoco