Attacher: make positionBySupport return if attached or not

Needed as reliable way of testing if attachment is working or not.

src/Mod/Part/App/AttachableObject.cpp

@@ -70,15 +70,17 @@ void AttachableObject::setAttacher(AttachEngine* attacher)
     updateAttacherVals();
 }
 
-void AttachableObject::positionBySupport()
+bool AttachableObject::positionBySupport()
 {
     if (!_attacher)
         throw Base::Exception("AttachableObject: can't positionBySupport, because no AttachEngine is set.");
     updateAttacherVals();
     try{
         this->Placement.setValue(_attacher->calculateAttachedPlacement(this->Placement.getValue()));
+        return true;
     } catch (ExceptionCancel) {
         //disabled, don't do anything
+        return false;
     };
 }
 
@@ -107,6 +109,7 @@ void setReadonlyness(App::Property &prop, bool on)
 void AttachableObject::onChanged(const App::Property* prop)
 {
     if(! this->isRestoring()){
+        bool bAttached = false;
         try{
             if ((prop == &Support
                  || prop == &MapMode
@@ -114,11 +117,7 @@ void AttachableObject::onChanged(const App::Property* prop)
                  || prop == &MapReversed
                  || prop == &superPlacement)){
 
-                eMapMode mmode = eMapMode(this->MapMode.getValue());
-                setReadonlyness(this->superPlacement, mmode == mmDeactivated);
-                setReadonlyness(this->Placement, mmode != mmDeactivated && mmode != mmTranslate);
-
-                positionBySupport();
+                bAttached = positionBySupport();
             }
         } catch (Base::Exception &e) {
             this->setError();
@@ -128,6 +127,11 @@ void AttachableObject::onChanged(const App::Property* prop)
             this->setError();
             Base::Console().Error("PositionBySupport: %s",e.GetMessageString());
         }
+
+        eMapMode mmode = eMapMode(this->MapMode.getValue());
+        setReadonlyness(this->superPlacement, !bAttached);
+        setReadonlyness(this->Placement, bAttached && mmode != mmTranslate); //for mmTranslate, orientation should remain editable even when attached.
+
     }
     Part::Feature::onChanged(prop);
 }

src/Mod/Part/App/AttachableObject.h

@@ -84,9 +84,10 @@ public:
     App::PropertyFloat MapPathParameter;
 
     /** calculate and update the Placement property based on the Support, and
-      * mode. Can throw FreeCAD and OCC exceptions.
+      * mode. Can throw FreeCAD and OCC exceptions. Returns true if attached,
+      * false if not, throws if attachment failed.
       */
-    virtual void positionBySupport(void);
+    virtual bool positionBySupport(void);
 
     virtual bool isTouched_Mapping()
     {return true; /*support.isTouched isn't true when linked objects are changed... why?..*/};

src/Mod/Part/App/Part2DObjectPy.xml

@@ -15,7 +15,9 @@
     </Documentation>
     <Methode Name="positionBySupport">
       <Documentation>
-        <UserDocu>Reposition object based on Support, MapMode and MapPathParameter properties.</UserDocu>
+        <UserDocu>positionBySupport(): Reposition object based on Support, MapMode and MapPathParameter properties.
+Returns True if attachment calculation was successful, false if object is not attached and Placement wasn't updated,
+and raises an exception if attachment calculation fails.</UserDocu>
       </Documentation>
     </Methode>
   </PythonExport>

src/Mod/Part/App/Part2DObjectPyImp.cpp

@@ -20,8 +20,9 @@ PyObject* Part2DObjectPy::positionBySupport(PyObject *args)
 {
     if (!PyArg_ParseTuple(args, ""))
         return 0;
+    bool bAttached = false;
     try{
-        this->getPart2DObjectPtr()->positionBySupport();
+        bAttached = this->getPart2DObjectPtr()->positionBySupport();
     } catch (Standard_Failure) {
         Handle_Standard_Failure e = Standard_Failure::Caught();
         PyErr_SetString(PartExceptionOCCError, e->GetMessageString());
@@ -30,8 +31,7 @@ PyObject* Part2DObjectPy::positionBySupport(PyObject *args)
         PyErr_SetString(Base::BaseExceptionFreeCADError, e.what());
         return NULL;
     }
-    Py_INCREF(Py_None);
-    return Py_None;
+    return Py::new_reference_to(Py::Boolean(bAttached));
 }