Add plugin tests for mjSpec.

Fixes #1903.

PiperOrigin-RevId: 663352920
Change-Id: I3a9e17aec5694e49c20b542f4b0a4402f88a2f17

python/mujoco/codegen/generate_spec_bindings.py

@@ -39,8 +39,10 @@ def _value_binding_code(
     fullvarname = 'ptr->' + varname
   if field.name.startswith('mjs'):  # all other mjs are raw structs
     fulltype = field.name.replace('mjs', 'raw::Mjs')
-    if field.name != 'mjsPlugin' and field.name != 'mjsOrientation':
-      fulltype = fulltype + '*'  # plugin and orientation are pointers
+    if field.name == 'mjsPlugin' or field.name == 'mjsOrientation':
+      fulltype = fulltype + '&'  # plugin and orientation are not pointers
+    else:
+      fulltype = fulltype + '*'
 
   def_property_args = (
       f'"{varname}"',

python/mujoco/specs.cc

@@ -1017,9 +1017,12 @@ PYBIND11_MODULE(_specs, m) {
   mjsTuple.def("delete", [](raw::MjsTuple& self) { mjs_delete(self.element); });
 
   // ============================= MJSPLUGIN ===================================
-  mjsPlugin.def_property_readonly("id", [](raw::MjsPlugin& self) -> int {
-    return mjs_getId(self.instance);
-  });
+  mjsPlugin.def_property(
+      "id",
+      [](raw::MjsPlugin& self) -> int { return mjs_getId(self.instance); },
+      [](raw::MjsPlugin& self, raw::MjsPlugin* other) {
+        self.instance = other->instance;
+      });
   mjsPlugin.def("delete",
                 [](raw::MjsPlugin& self) { mjs_delete(self.instance); });
 

python/mujoco/specs_test.py

@@ -322,5 +322,35 @@ class SpecsTest(absltest.TestCase):
     self.assertEqual(model.nsite, 10)
     self.assertEqual(model.nsensor, 9)
 
+  def test_plugin(self):
+    xml = """
+    <mujoco>
+      <extension>
+        <plugin plugin="mujoco.elasticity.cable"/>
+      </extension>
+    </mujoco>
+    """
+
+    spec = mujoco.MjSpec()
+    spec.from_string(xml)
+    self.assertIsNotNone(spec.worldbody)
+
+    body = spec.worldbody.add_body()
+    body.plugin.name = 'mujoco.elasticity.cable'
+    body.plugin.id = spec.add_plugin()
+    body.plugin.active = True
+    self.assertEqual(body.plugin.id, 0)
+
+    geom = body.add_geom()
+    geom.type = mujoco.mjtGeom.mjGEOM_BOX
+    geom.size[0] = 1
+    geom.size[1] = 1
+    geom.size[2] = 1
+
+    model = spec.compile()
+    self.assertIsNotNone(model)
+    self.assertEqual(model.nplugin, 1)
+    self.assertEqual(model.body_plugin[1], 0)
+
 if __name__ == '__main__':
   absltest.main()

src/user/user_api.cc

@@ -606,6 +606,9 @@ const char* mjs_resolveOrientation(double quat[4], mjtByte degree, const char* s
 
 // get id
 int mjs_getId(mjsElement* element) {
+  if (!element) {
+    return -1;
+  }
   return static_cast<mjCBase*>(element)->id;
 }
 

test/user/user_api_test.cc

@@ -20,6 +20,7 @@
 #include <filesystem>
 #include <memory>
 #include <string>
+#include <utility>
 #include <vector>
 
 #include <gmock/gmock.h>
@@ -104,6 +105,41 @@ TEST_F(MujocoTest, TreeTraversal) {
   mj_deleteSpec(spec);
 }
 
+TEST_F(PluginTest, ActivatePlugin) {
+  std::string plugin_name = "mujoco.elasticity.cable";
+  mjSpec* spec = mj_makeSpec();
+
+  // get slot of requested plugin
+  int plugin_slot = -1;
+  const mjpPlugin* plugin = mjp_getPlugin(plugin_name.c_str(), &plugin_slot);
+  EXPECT_THAT(plugin, NotNull());
+
+  // activated plugin in the slot
+  std::vector<std::pair<const mjpPlugin*, int>> active_plugins;
+  active_plugins.emplace_back(std::make_pair(plugin, plugin_slot));
+  mjs_setActivePlugins(spec, &active_plugins);
+
+  // associate plugin to body
+  mjsBody* body = mjs_addBody(mjs_findBody(spec, "world"), 0);
+  mjs_setString(body->plugin.name, plugin_name.c_str());
+  body->plugin.instance = mjs_addPlugin(spec)->instance;
+  body->plugin.active = true;
+  mjsGeom* geom = mjs_addGeom(body, 0);
+  geom->type = mjGEOM_BOX;
+  geom->size[0] = 1;
+  geom->size[1] = 1;
+  geom->size[2] = 1;
+
+  // compile and check that the plugin is present
+  mjModel* model = mj_compile(spec, NULL);
+  EXPECT_THAT(model, NotNull());
+  EXPECT_THAT(model->nplugin, 1);
+  EXPECT_THAT(model->body_plugin[1], 0);
+
+  mj_deleteSpec(spec);
+  mj_deleteModel(model);
+}
+
 // ------------------- test recompilation multiple files -----------------------
 TEST_F(PluginTest, RecompileCompare) {
   mjtNum tol = 0;