Improve error message for fullinertia and orientation specifiers.

Fixes #1888.

PiperOrigin-RevId: 661359190
Change-Id: Ibe38e88024b4a43922352b42347abf1026f168a2

src/xml/xml_native_reader.cc

@@ -3344,7 +3344,7 @@ void mjXReader::Body(XMLElement* section, mjsBody* pbody, mjsFrame* frame,
       bool alt = ReadAlternative(elem, pbody->ialt);
       bool full = ReadAttr(elem, "fullinertia", 6, pbody->fullinertia, text);
       if (alt && full) {
-        throw mjXError(elem, "multiple orientation specifiers are not allowed");
+        throw mjXError(elem, "fullinertia and orientation specifiers cannot be used together");
       }
     }
 

test/xml/xml_native_reader_test.cc

@@ -1637,8 +1637,10 @@ TEST_F(XMLReaderTest, InvalidInertialOrientation) {
   std::array<char, 1024> error;
   mjModel* model = LoadModelFromString(xml, error.data(), error.size());
   ASSERT_THAT(model, IsNull());
-  EXPECT_THAT(error.data(),
-              HasSubstr("multiple orientation specifiers are not allowed"));
+  EXPECT_THAT(
+      error.data(),
+      HasSubstr(
+          "fullinertia and orientation specifiers cannot be used together"));
 }
 
 TEST_F(XMLReaderTest, ReadShellParameter) {