fixes 0003680: Export (Ctrl+E) doesn't check to make sure that object being exported is a model at all

src/Mod/Mesh/App/AppMeshPy.cpp

@@ -322,6 +322,33 @@ private:
             return Py::None();
         }
 
+        // collect all object types that can be exported as mesh
+        std::vector<App::DocumentObject*> objectList;
+        std::string label;
+        for (auto it : list) {
+            PyObject *item = it.ptr();
+            if (PyObject_TypeCheck(item, &(App::DocumentObjectPy::Type))) {
+                auto obj( static_cast<App::DocumentObjectPy *>(item)->getDocumentObjectPtr() );
+                label = obj->Label.getValue();
+                if (Exporter::isSupported(obj))
+                    objectList.push_back(obj);
+            }
+        }
+
+        if (objectList.empty()) {
+            std::string errorMessage;
+            if (list.length() == 1) {
+                std::stringstream str;
+                str << label << " cannot be exported to a mesh file";
+                errorMessage = str.str();
+            }
+            else {
+                errorMessage = "None of the objects can be exported to a mesh file";
+            }
+
+            throw Py::TypeError(errorMessage);
+        }
+
         auto exportFormat( MeshOutput::GetFormat(outputFileName.c_str()) );
 
         std::unique_ptr<Exporter> exporter;
@@ -343,13 +370,8 @@ private:
             throw Py::Exception(Base::BaseExceptionFreeCADError, exStr.c_str());
         }
 
-        for (auto it : list) {
-            PyObject *item = it.ptr();
-            if (PyObject_TypeCheck(item, &(App::DocumentObjectPy::Type))) {
-                auto obj( static_cast<App::DocumentObjectPy *>(item)->getDocumentObjectPtr() );
-
-                exporter->addObject(obj, fTolerance);
-            }
+        for (auto it : objectList) {
+            exporter->addObject(it, fTolerance);
         }
         exporter.reset();   // deletes Exporter, mesh file is written by destructor
 

src/Mod/Mesh/App/Exporter.cpp

@@ -63,6 +63,30 @@ std::string Exporter::xmlEscape(const std::string &input)
     return out;
 }
 
+bool Exporter::isSupported(App::DocumentObject *obj)
+{
+    Base::Type meshFeatId(Base::Type::fromName("Mesh::Feature"));
+    Base::Type appPartId(Base::Type::fromName("Part::Feature"));
+    Base::Type groupExtensionId(App::GroupExtension::getExtensionClassTypeId());
+
+    if (obj->getTypeId().isDerivedFrom(meshFeatId)) {
+        return true;
+    }
+    else if (obj->getTypeId().isDerivedFrom(appPartId)) {
+        return true;
+    }
+    else if (obj->hasExtension(groupExtensionId)) {
+        auto groupEx( obj->getExtensionByType<App::GroupExtension>() );
+        for (auto it : groupEx->Group.getValues()) {
+            bool ok = isSupported(it);
+            if (ok)
+                return true;
+        }
+    }
+
+    return false;
+}
+
 bool Exporter::addAppGroup(App::DocumentObject *obj, float tol)
 {
     auto ret(true);

src/Mod/Mesh/App/Exporter.h

@@ -52,6 +52,11 @@ class Exporter
     public:
         Exporter();
 
+        /*!
+         * \return true if \a is an object that can be exported as mesh.
+         */
+        static bool isSupported(App::DocumentObject *obj);
+
         virtual bool addMeshFeat(App::DocumentObject *obj) = 0;
         virtual bool addPartFeat(App::DocumentObject *obj, float tol) = 0;