Gui: [skip ci] fix Gui.subgraphFromObject and improve error text if wrapping fails

src/Base/swigpyrun.cpp

@@ -24,6 +24,7 @@
 #include "PreCompiled.h"
 #include "PyExport.h"
 #include "Exception.h"
+#include <sstream>
 #if (defined(HAVE_SWIG) && (HAVE_SWIG == 1))
 #if defined(__clang__)
 # pragma clang diagnostic push

src/Base/swigpyrun.inl

@@ -29,8 +29,11 @@ int createSWIGPointerObj_T(const char* TypeName, void* obj, PyObject** ptr, int
 
     swig_type_info * swig_type = 0;
     swig_type = SWIG_TypeQuery(TypeName);
-    if (!swig_type)
-        throw Base::RuntimeError("Cannot find type information for requested type");
+    if (!swig_type) {
+        std::stringstream str;
+        str << "SWIG: Cannot find type information for requested type: " << TypeName;
+        throw Base::RuntimeError(str.str());
+    }
     
     *ptr = SWIG_NewPointerObj(obj,swig_type,own);
     if (*ptr == 0)

src/Gui/Application.cpp

@@ -201,8 +201,16 @@ FreeCADGui_subgraphFromObject(PyObject * /*self*/, PyObject *args)
                 vp->setDisplayMode(modes.front().c_str());
             node = vp->getRoot()->copy();
             node->ref();
-            std::string type = "So";
-            type += node->getTypeId().getName().getString();
+            std::string prefix = "So";
+            std::string type = node->getTypeId().getName().getString();
+            // doesn't start with the prefix 'So'
+            if (type.rfind("So", 0) != 0) {
+                type = prefix + type;
+            }
+            else if (type == "SoFCSelectionRoot") {
+                type = "SoSeparator";
+            }
+
             type += " *";
             PyObject* proxy = 0;
             proxy = Base::Interpreter().createSWIGPointerObj("pivy.coin", type.c_str(), (void*)node, 1);