Skip serializing nested model with //pose/@relative_to attribute (#1454)

This PR prevents serialization of a model component if it has the //pose/@relative_to attribute to avoid flooding the console with error messages when there are multiple models with nested models using this attribute. Since model deserialization with //pose/@relative_to never worked, this should not affect existing behavior. I believe the model serialization / deserialization functionality is mainly used by the component editor. Related issue: #1071

Signed-off-by: Ian Chen <[email protected]>

examples/worlds/sensors_demo.sdf

@@ -380,6 +380,7 @@
             <image>
               <width>320</width>
               <height>240</height>
+              <format>L8</format>
             </image>
             <clip>
               <near>0.1</near>

include/ignition/gazebo/components/Model.hh

@@ -46,13 +46,38 @@ namespace serializers
       sdf::ElementPtr modelElem = _model.Element();
       if (!modelElem)
       {
-        ignerr << "Unable to serialize sdf::Model" << std::endl;
+        ignwarn << "Unable to serialize sdf::Model" << std::endl;
         return _out;
       }
 
+      bool skip = false;
+      if (modelElem->HasElement("pose"))
+      {
+        sdf::ElementPtr poseElem = modelElem->GetElement("pose");
+        if (poseElem->HasAttribute("relative_to"))
+        {
+          // Skip serializing models with //pose/@relative_to attribute
+          // since deserialization will fail. This could be a nested model.
+          // see https://github.com/ignitionrobotics/ign-gazebo/issues/1071
+          // Once https://github.com/ignitionrobotics/sdformat/issues/820 is
+          // resolved, there should be an API that returns sdf::Errors objects
+          // instead of printing console msgs so it would be easier to ignore
+          // specific errors in Deserialize.
+          static bool warned = false;
+          if (!warned)
+          {
+            ignwarn << "Skipping serialization / deserialization for models "
+                    << "with //pose/@relative_to attribute."
+                    << std::endl;
+            warned = true;
+          }
+          skip = true;
+        }
+      }
+
       _out << "<?xml version=\"1.0\" ?>"
            << "<sdf version='" << SDF_PROTOCOL_VERSION << "'>"
-           << modelElem->ToString("")
+           << (skip ? std::string() : modelElem->ToString(""))
            << "</sdf>";
       return _out;
     }
@@ -70,7 +95,7 @@ namespace serializers
       sdf::Errors errors = root.LoadSdfString(sdf);
       if (!root.Model())
       {
-        ignerr << "Unable to unserialize sdf::Model" << std::endl;
+        ignwarn << "Unable to deserialize sdf::Model" << std::endl;
         return _in;
       }