7846: Prevent creation of a place cycle when merging

gramps/gen/utils/location.py

@@ -90,3 +90,26 @@ def get_locations(db, place):
         if len(place.get_placeref_list()) == 0:
             locations.append(dict(tree))
     return locations
+
+#-------------------------------------------------------------------------
+#
+# located_in
+#
+#-------------------------------------------------------------------------
+def located_in(db, handle1, handle2):
+    """
+    Determine if the place identified by handle1 is located within the place
+    identified by handle2.
+    """
+    place = db.get_place_from_handle(handle1)
+    todo = [(place, [handle1])]
+    while len(todo):
+        place, visited = todo.pop()
+        for parent in place.get_placeref_list():
+            if parent.ref == handle2:
+                return True
+            if parent.ref not in visited:
+                parent_place = db.get_place_from_handle(parent.ref)
+                parent_visited = visited + [parent.ref]
+                todo.append((parent_place, parent_visited))
+    return False

gramps/plugins/lib/libplaceview.py

@@ -57,6 +57,7 @@ from gramps.gui.editors import EditPlace, DeletePlaceQuery
 from gramps.gui.filters.sidebar import PlaceSidebarFilter
 from gramps.gui.merge import MergePlace
 from gramps.gen.plug import CATEGORY_QR_PLACE
+from gramps.gen.utils.location import located_in
 
 #-------------------------------------------------------------------------
 #
@@ -413,8 +414,15 @@ class PlaceBaseView(ListView):
                      "control key while clicking on the desired place.")
             ErrorDialog(msg, msg2)
         else:
-            MergePlace(self.dbstate, self.uistate, mlist[0], mlist[1],
+            if (located_in(self.dbstate.db, mlist[0], mlist[1]) or
-                       self.merged)
+                located_in(self.dbstate.db, mlist[1], mlist[0])):
+                msg = _("Cannot merge places.")
+                msg2 = _("Merging these places would create a cycle in the "
+                         "place hierarchy.")
+                ErrorDialog(msg, msg2)
+            else:
+                MergePlace(self.dbstate, self.uistate, mlist[0], mlist[1],
+                           self.merged)
 
     def merged(self):
         """