Capture mjs_attach error message in the Python bindings.

PiperOrigin-RevId: 682409212
Change-Id: I391ee48626e7dcd985f65a231370ef5ec16124d7

doc/APIreference/functions.rst

@@ -4126,6 +4126,15 @@ mjs_getSpec
 
 Get spec from body.
 
+.. _mjs_getSpecFromFrame:
+
+mjs_getSpecFromFrame
+~~~~~~~~~~~~~~~~~~~~
+
+.. mujoco-include:: mjs_getSpecFromFrame
+
+Get spec from frame.
+
 .. _mjs_findBody:
 
 mjs_findBody

doc/includes/references.h

@@ -3590,6 +3590,7 @@ mjsSkin* mjs_addSkin(mjSpec* s);
 mjsTexture* mjs_addTexture(mjSpec* s);
 mjsMaterial* mjs_addMaterial(mjSpec* s, mjsDefault* def);
 mjSpec* mjs_getSpec(mjsBody* body);
+mjSpec* mjs_getSpecFromFrame(mjsFrame* frame);
 mjsBody* mjs_findBody(mjSpec* s, const char* name);
 mjsElement* mjs_findElement(mjSpec* s, mjtObj type, const char* name);
 mjsBody* mjs_findChild(mjsBody* body, const char* name);

include/mujoco/mujoco.h

@@ -1526,6 +1526,9 @@ MJAPI mjsMaterial* mjs_addMaterial(mjSpec* s, mjsDefault* def);
 // Get spec from body.
 MJAPI mjSpec* mjs_getSpec(mjsBody* body);
 
+// Get spec from frame.
+MJAPI mjSpec* mjs_getSpecFromFrame(mjsFrame* frame);
+
 // Find body in spec by name.
 MJAPI mjsBody* mjs_findBody(mjSpec* s, const char* name);
 

introspect/functions.py

@@ -9682,6 +9682,22 @@ FUNCTIONS: Mapping[str, FunctionDecl] = dict([
          ),
          doc='Get spec from body.',
      )),
+    ('mjs_getSpecFromFrame',
+     FunctionDecl(
+         name='mjs_getSpecFromFrame',
+         return_type=PointerType(
+             inner_type=ValueType(name='mjSpec'),
+         ),
+         parameters=(
+             FunctionParameterDecl(
+                 name='frame',
+                 type=PointerType(
+                     inner_type=ValueType(name='mjsFrame'),
+                 ),
+             ),
+         ),
+         doc='Get spec from frame.',
+     )),
     ('mjs_findBody',
      FunctionDecl(
          name='mjs_findBody',

python/mujoco/specs.cc

@@ -563,7 +563,12 @@ PYBIND11_MODULE(_specs, m) {
       "attach_frame",
       [](raw::MjsBody& self, raw::MjsFrame& frame, std::string& prefix,
          std::string& suffix) -> raw::MjsFrame* {
-        return mjs_attachFrame(&self, &frame, prefix.c_str(), suffix.c_str());
+        auto new_frame =
+            mjs_attachFrame(&self, &frame, prefix.c_str(), suffix.c_str());
+        if (!new_frame) {
+          throw pybind11::value_error(mjs_getError(mjs_getSpec(&self)));
+        }
+        return new_frame;
       },
       py::return_value_policy::reference_internal);
 
@@ -578,7 +583,13 @@ PYBIND11_MODULE(_specs, m) {
       "attach_body",
       [](raw::MjsFrame& self, raw::MjsBody& body, std::string& prefix,
          std::string& suffix) -> raw::MjsBody* {
-        return mjs_attachBody(&self, &body, prefix.c_str(), suffix.c_str());
+        auto new_body =
+            mjs_attachBody(&self, &body, prefix.c_str(), suffix.c_str());
+        if (!new_body) {
+          throw pybind11::value_error(
+              mjs_getError(mjs_getSpecFromFrame(&self)));
+        }
+        return new_body;
       },
       py::return_value_policy::reference_internal);
 

python/mujoco/specs_test.py

@@ -846,5 +846,20 @@ class SpecsTest(absltest.TestCase):
     with self.assertRaises(IndexError):
       material.textures[-1] = 'x'
 
+  def test_attach_error(self):
+    child = mujoco.MjSpec()
+    parent = mujoco.MjSpec()
+    parent.degree = not child.degree
+    body = parent.worldbody.add_body()
+    frame = child.worldbody.add_frame()
+    with self.assertRaises(ValueError) as cm:
+      body.attach_frame(frame, '', '')
+    self.assertEqual(
+        str(cm.exception),
+        'Error: cannot attach mjSpecs with incompatible compiler/angle'
+        ' attribute',
+    )
+
+
 if __name__ == '__main__':
   absltest.main()

src/user/user_api.cc

@@ -521,13 +521,20 @@ mjsDefault* mjs_addDefault(mjSpec* s, const char* classname, const mjsDefault* p
 
 
 
-// get objects
+// get spec from body
 mjSpec* mjs_getSpec(mjsBody* body) {
   return &(static_cast<mjCBody*>(body->element)->model->spec);
 }
 
 
 
+// get spec from frame
+mjSpec* mjs_getSpecFromFrame(mjsFrame* frame) {
+  return &(static_cast<mjCFrame*>(frame->element)->model->spec);
+}
+
+
+
 // find spec (model asset) by name
 mjSpec* mjs_findSpec(mjSpec* s, const char* name) {
   mjCModel* model = static_cast<mjCModel*>(s->element);

src/user/user_api.h

@@ -188,6 +188,9 @@ MJAPI mjsMaterial* mjs_addMaterial(mjSpec* s, mjsDefault* def);
 // Get spec from body.
 MJAPI mjSpec* mjs_getSpec(mjsBody* body);
 
+// Get spec from frame.
+MJAPI mjSpec* mjs_getSpecFromFrame(mjsFrame* frame);
+
 // Find spec (model asset) by name.
 MJAPI mjSpec* mjs_findSpec(mjSpec* spec, const char* name);