+ on rename of contraint make sure that new name is different, on swap constraint names make sure they have user-defined names

src/Mod/Sketcher/App/PropertyConstraintList.cpp

@@ -386,7 +386,7 @@ bool PropertyConstraintList::scanGeometry(const std::vector<Part::Geometry *> &G
 
 string PropertyConstraintList::getConstraintName(const std::string & name, int i)
 {
-    if (name != "")
+    if (!name.empty())
         return name;
     else
         return getConstraintName(i);

src/Mod/Sketcher/App/SketchObjectPyImp.cpp

@@ -355,11 +355,14 @@ PyObject* SketchObjectPy::renameConstraint(PyObject *args)
         }
     }
 
-    Constraint* copy = this->getSketchObjectPtr()->Constraints[Index]->clone();
-    copy->Name = Name;
-    this->getSketchObjectPtr()->Constraints.set1Value(Index, copy);
-    delete copy;
-
+    // only change the constraint item if the names are different
+    const Constraint* item = this->getSketchObjectPtr()->Constraints[Index];
+    if (item->Name != Name) {
+        Constraint* copy = item->clone();
+        copy->Name = Name;
+        this->getSketchObjectPtr()->Constraints.set1Value(Index, copy);
+        delete copy;
+    }
     Py_Return;
 }
 

src/Mod/Sketcher/Gui/TaskSketcherConstrains.cpp

@@ -476,8 +476,19 @@ void ConstraintView::swapNamedOfSelectedItems()
     std::string escapedstr1 = Base::Tools::escapedUnicodeFromUtf8(item1->sketch->Constraints[item1->ConstraintNbr]->Name.c_str());
     ConstraintItem * item2 = static_cast<ConstraintItem*>(items[1]);
     std::string escapedstr2 = Base::Tools::escapedUnicodeFromUtf8(item2->sketch->Constraints[item2->ConstraintNbr]->Name.c_str());
-    std::stringstream ss;
 
+    // In commit 67800ec8c (21 Jul 2015) the implementation of on_listWidgetConstraints_itemChanged()
+    // has changed ensuring that a name of a constraint cannot be reset any more.
+    // This leads to some inconsistencies when trying to swap "empty" names.
+    //
+    // If names are empty then nothing should be done
+    if (escapedstr1.empty() || escapedstr2.empty()) {
+        QMessageBox::warning(Gui::MainWindow::getInstance(), tr("Unnamed constraint"),
+                             tr("Only the names of named constraints can be swapped."));
+        return;
+    }
+
+    std::stringstream ss;
     ss << "DummyConstraint" << rand();
     std::string tmpname = ss.str();
 
@@ -673,7 +684,7 @@ void TaskSketcherConstrains::on_listWidgetConstraints_itemChanged(QListWidgetIte
         catch (const Base::Exception & e) {
             Gui::Command::abortCommand();
 
-            QMessageBox::critical(Gui::MainWindow::getInstance(), QString::fromLatin1("Error"),
+            QMessageBox::critical(Gui::MainWindow::getInstance(), tr("Error"),
                                   QString::fromLatin1(e.what()), QMessageBox::Ok, QMessageBox::Ok);
         }
     }