Added APIs to allow users set the flag: _children_on_boundary

The motivaiton is that: "automatic" way might not work for cases.

For example, if the flag is on on a subset of processor cores, and
then we do reparitioning, and then we might hit trouble because
the flag is off on the other processors

I try to avoid having a global reduction to have everyone on the same page.
In fact, we know when we want to allow children on boundary in MOOSE.
In this case, we should set the flag to make the code more robust

include/mesh/boundary_info.h

@@ -874,6 +874,18 @@ class BoundaryInfo : public ParallelObject
   const std::multimap<const Elem *, std::pair<unsigned short int, boundary_id_type>> & get_sideset_map() const
   { return _boundary_side_id; }
 
+  /**
+   * \returns Whether or not there are some children on boundary sides
+   */
+  bool is_children_on_boundary_side() const
+  { return _children_on_boundary; }
+
+  /**
+   * Whether or not to allow set boundary sides on children elements
+   */
+  void allow_children_on_boundary_side(const bool children_on_boundary)
+  { _children_on_boundary = children_on_boundary; }
+
 private:
 
   /**

src/mesh/boundary_info.C

@@ -1364,8 +1364,8 @@ void BoundaryInfo::remove_edge (const Elem * elem,
 {
   libmesh_assert(elem);
 
-  // Only level 0 elements unless the flag "_children_on_boundary" is on.
-  libmesh_assert(elem->level()==0 || _children_on_boundary);
+  // Only level 0 elements are stored in BoundaryInfo.
+  libmesh_assert_equal_to (elem->level(), 0);
 
   // Erase (elem, edge, *) entries from map.
   erase_if(_boundary_edge_id, elem,
@@ -1381,8 +1381,8 @@ void BoundaryInfo::remove_edge (const Elem * elem,
 {
   libmesh_assert(elem);
 
-  // Only level 0 elements unless the flag "_children_on_boundary" is on.
-  libmesh_assert(elem->level() == 0 || _children_on_boundary);
+  // Only level 0 elements are stored in BoundaryInfo.
+  libmesh_assert_equal_to (elem->level(), 0);
 
   // Erase (elem, edge, id) entries from map.
   erase_if(_boundary_edge_id, elem,
@@ -1396,8 +1396,8 @@ void BoundaryInfo::remove_shellface (const Elem * elem,
 {
   libmesh_assert(elem);
 
-  // Only level 0 elements unless the flag "_children_on_boundary" is on.
-  libmesh_assert(elem->level() == 0 || _children_on_boundary);
+  // Only level 0 elements are stored in BoundaryInfo.
+  libmesh_assert_equal_to (elem->level(), 0);
 
   // Shells only have 2 faces
   libmesh_assert_less(shellface, 2);
@@ -1416,8 +1416,8 @@ void BoundaryInfo::remove_shellface (const Elem * elem,
 {
   libmesh_assert(elem);
 
-  // Only level 0 elements unless the flag "_children_on_boundary" is on.
-  libmesh_assert(elem->level() == 0 || _children_on_boundary);
+  // Only level 0 elements are stored in BoundaryInfo.
+  libmesh_assert_equal_to (elem->level(), 0);
 
   // Shells only have 2 faces
   libmesh_assert_less(shellface, 2);
@@ -1508,6 +1508,8 @@ unsigned int BoundaryInfo::side_with_boundary_id(const Elem * const elem,
   // parent if any
   if (elem->level() != 0)
     searched_elem_vec.push_back(elem->top_parent());
+  else if (!_children_on_boundary)
+    searched_elem_vec.push_back(elem);
 
   for (auto it = searched_elem_vec.begin(); it != searched_elem_vec.end(); ++it)
   {
@@ -1567,6 +1569,8 @@ BoundaryInfo::sides_with_boundary_id(const Elem * const elem,
   // Return boundary information of its parent as well
   if (elem->level() != 0)
     searched_elem_vec.push_back(elem->top_parent());
+  else if (!_children_on_boundary)
+    searched_elem_vec.push_back(elem);
 
   for (auto it = searched_elem_vec.begin(); it != searched_elem_vec.end(); ++it)
   {