Add suffix to duplicated assets.

PiperOrigin-RevId: 588775467
Change-Id: I3a0d2a14601cf018b0c8c56728bd3ae22adb8ec2

test/user/testdata/load_twice.xml

@@ -0,0 +1,10 @@
+<mujoco>
+  <asset>
+    <mesh file="cube.obj"/>
+    <mesh file="cube.obj"/>
+  </asset>
+  <worldbody>
+    <geom type="mesh" mesh="cube_0"/>
+    <geom type="mesh" mesh="cube_1"/>
+  </worldbody>
+</mujoco>

test/user/user_model_test.cc

@@ -14,6 +14,7 @@
 
 // Tests for user/user_model.cc.
 
+#include <array>
 #include <string>
 
 #include <gmock/gmock.h>
@@ -21,6 +22,7 @@
 #include <absl/strings/str_format.h>
 #include <mujoco/mjmodel.h>
 #include <mujoco/mujoco.h>
+#include "src/cc/array_safety.h"
 #include "test/fixture.h"
 
 namespace mujoco {
@@ -190,6 +192,26 @@ TEST_F(UserDataTest, AutoNUserSensor) {
   mj_deleteModel(m);
 }
 
+// ------------- test duplicate names ------------------------------------------
+TEST_F(UserDataTest, DuplicateNames) {
+  static const char* const kFilePath = "user/testdata/load_twice.xml";
+  const std::string xml_path = GetTestDataFilePath(kFilePath);
+
+  std::array<char, 1024> error;
+  mjModel* m = mj_loadXML(xml_path.c_str(), 0, error.data(), error.size());
+
+  EXPECT_THAT(m, NotNull()) << error.data();
+  EXPECT_THAT(m->nmesh, 2);
+
+  for (int i = 0; i < m->nmesh; i++) {
+    char mesh_name[mjMAXUINAME] = "";
+    util::strcat_arr(mesh_name, m->names + m->name_meshadr[i]);
+    EXPECT_THAT(std::string(mesh_name), "cube_" + std::to_string(i));
+  }
+
+  mj_deleteModel(m);
+}
+
 // ------------- test fusestatic -----------------------------------------------
 
 using FuseStaticTest = MujocoTest;