Attacher: Py: add interface for changing attacher type

Plus a mechanism to remember attacher type of AttachableObject through
save-restore cycle.

src/Mod/Part/App/AttachableObject.cpp

@@ -42,6 +42,9 @@ PROPERTY_SOURCE(Part::AttachableObject, Part::Feature);
 AttachableObject::AttachableObject()
    :  _attacher(0)
 {
+    ADD_PROPERTY_TYPE(AttacherType, ("Attacher::AttachEngine3D"), "Attachment",(App::PropertyType)(App::Prop_None),"Class name of attach engine object driving the attachment.");
+    this->AttacherType.setStatus(App::Property::Status::Hidden, true);
+
     ADD_PROPERTY_TYPE(Support, (0,0), "Attachment",(App::PropertyType)(App::Prop_None),"Support of the 2D geometry");
 
     ADD_PROPERTY_TYPE(MapMode, (mmDeactivated), "Attachment", App::Prop_None, "Mode of attachment to other object");
@@ -69,7 +72,44 @@ void AttachableObject::setAttacher(AttachEngine* attacher)
     if (_attacher)
         delete _attacher;
     _attacher = attacher;
-    updateAttacherVals();
+    if (_attacher){
+        const char* typeName = attacher->getTypeId().getName();
+        if(strcmp(this->AttacherType.getValue(),typeName)!=0) //make sure we need to change, to break recursive onChange->changeAttacherType->onChange...
+            this->AttacherType.setValue(typeName);
+        updateAttacherVals();
+    } else {
+        if (strlen(AttacherType.getValue()) != 0){ //make sure we need to change, to break recursive onChange->changeAttacherType->onChange...
+            this->AttacherType.setValue("");
+        }
+    }
+}
+
+bool AttachableObject::changeAttacherType(const char* typeName)
+{
+    //check if we need to actually change anything
+    if (_attacher){
+        if (strcmp(_attacher->getTypeId().getName(),typeName)==0){
+            return false;
+        }
+    } else if (strlen(typeName) == 0){
+        return false;
+    }
+    if (strlen(typeName) == 0){
+        setAttacher(nullptr);
+        return true;
+    }
+    Base::Type t = Base::Type::fromName(typeName);
+    if (t.isDerivedFrom(AttachEngine::getClassTypeId())){
+        AttachEngine* pNewAttacher = static_cast<Attacher::AttachEngine*>(Base::Type::createInstanceByName(typeName));
+        this->setAttacher(pNewAttacher);
+        return true;
+    } else {
+        std::stringstream errMsg;
+        errMsg << "Object if this type is not derived from AttachEngine: " << typeName;
+        throw Base::Exception(errMsg.str());
+    }
+    assert(false);//exec shouldn't ever get here
+    return false;
 }
 
 bool AttachableObject::positionBySupport()
@@ -138,6 +178,10 @@ void AttachableObject::onChanged(const App::Property* prop)
 
     }
 
+    if(prop == &(this->AttacherType)){
+        this->changeAttacherType(this->AttacherType.getValue());
+    }
+
     Part::Feature::onChanged(prop);
 }
 

src/Mod/Part/App/AttachableObject.h

@@ -68,9 +68,20 @@ public:
      * @param attacher. AttachableObject takes ownership and will delete it eventually.
      */
     virtual void setAttacher(Attacher::AttachEngine* attacher);
+
+    /**
+     * @brief changeAttacherType
+     * @param typeName is the typename of new attacher class. Must be derived
+     * from Attacher::AttachEngine.
+     * @return true if attacher was changed. false if attacher is already of the
+     * type requested. Throws if invalid type is supplied.
+     */
+    bool changeAttacherType(const char* typeName);
+
     Attacher::AttachEngine &attacher(void) const {return *_attacher;}
 
-    /// if the 2DObject lies on the Face of an other object this links to it
+
+    App::PropertyString         AttacherType;
     App::PropertyLinkSubList    Support;
     App::PropertyEnumeration    MapMode; //see AttachEngine::eMapMode
     App::PropertyBool           MapReversed; //inverts Z and X internal axes

src/Mod/Part/App/AttachableObjectPy.xml

@@ -20,5 +20,15 @@ Returns True if attachment calculation was successful, false if object is not at
 and raises an exception if attachment calculation fails.</UserDocu>
       </Documentation>
     </Methode>
+    <Methode Name = "changeAttacherType">
+      <Documentation>
+        <UserDocu>changeAttacherType(typename): Changes Attacher class of this object.
+typename: string. The following are accepted so far:
+'Attacher::AttachEngine3D'
+'Attacher::AttachEnginePlane'
+'Attacher::AttachEngineLine'
+'Attacher::AttachEnginePoint'</UserDocu>
+      </Documentation>
+    </Methode>
   </PythonExport>
 </GenerateModel>

src/Mod/Part/App/AttachableObjectPyImp.cpp

@@ -34,6 +34,25 @@ PyObject* AttachableObjectPy::positionBySupport(PyObject *args)
     return Py::new_reference_to(Py::Boolean(bAttached));
 }
 
+PyObject* AttachableObjectPy::changeAttacherType(PyObject *args)
+{
+    const char* typeName;
+    if (!PyArg_ParseTuple(args, "s", &typeName))
+        return 0;
+    bool ret;
+    try{
+        ret = this->getAttachableObjectPtr()->changeAttacherType(typeName);
+    } catch (Standard_Failure) {
+        Handle_Standard_Failure e = Standard_Failure::Caught();
+        PyErr_SetString(PartExceptionOCCError, e->GetMessageString());
+        return NULL;
+    } catch (Base::Exception &e) {
+        PyErr_SetString(Base::BaseExceptionFreeCADError, e.what());
+        return NULL;
+    }
+    return Py::new_reference_to(Py::Boolean(ret));
+}
+
 
 PyObject *AttachableObjectPy::getCustomAttributes(const char* /*attr*/) const
 {