Refactor to use forward declarations and revert periodic neighbor logic

- Moved new MeshBase functions out of the header to use forward declarations, reducing unnecessary includes.
- Reverted the PeriodicBoundaries::neighbor() logic to allow self-matching, since the existing boundary ID check already prevents unintended self-detections in periodic boundary cases.

Author: ChengHauYang

include/base/periodic_boundaries.h

@@ -68,8 +68,7 @@ class PeriodicBoundaries : public std::map<boundary_id_type, std::unique_ptr<Per
                         const PointLocatorBase & point_locator,
                         const Elem * e,
                         unsigned int side,
-                        unsigned int * neigh_side = nullptr,
-                        bool skip_found_check = false) const;
+                        unsigned int * neigh_side = nullptr) const;
 };
 
 } // namespace libMesh

include/mesh/mesh_base.h

@@ -37,8 +37,12 @@
 #include <memory>
 
 // periodic boundary condition support
-#include "libmesh/periodic_boundaries.h"
-#include "libmesh/periodic_boundary.h"
+// Use forward declarations inside the libMesh namespace
+namespace libMesh
+{
+  class PeriodicBoundary;
+  class PeriodicBoundaries;
+}
 
 namespace libMesh
 {
@@ -1829,35 +1833,11 @@ class MeshBase : public ParallelObject
    * Register a pair of boundaries as disconnected boundaries.
    */
   void add_disconnected_boundaries(const boundary_id_type b1,
-                                  const boundary_id_type b2)
-    {
-      // Lazily allocate the container the first time it’s needed
-      if (!_disconnected_boundary_pairs)
-        _disconnected_boundary_pairs = std::make_unique<PeriodicBoundaries>();
-
-      // Create forward and inverse boundary mappings
-      PeriodicBoundary forward(RealVectorValue(0., 0., 0.));
-      PeriodicBoundary inverse(RealVectorValue(0., 0., 0.));
-
-      forward.myboundary       = b1;
-      forward.pairedboundary   = b2;
-      inverse.myboundary       = b2;
-      inverse.pairedboundary   = b1;
-
-      // Add both directions into the container
-      _disconnected_boundary_pairs->emplace(b1, forward.clone());
-      _disconnected_boundary_pairs->emplace(b2, inverse.clone());
-    }
-
-  PeriodicBoundaries * get_disconnected_boundaries()
-    {
-      return _disconnected_boundary_pairs.get();
-    }
-
-  const PeriodicBoundaries * get_disconnected_boundaries() const
-    {
-      return _disconnected_boundary_pairs.get();
-    }
+                                   const boundary_id_type b2);
+
+  PeriodicBoundaries * get_disconnected_boundaries();
+
+  const PeriodicBoundaries * get_disconnected_boundaries() const;
 #endif
 
 

src/base/periodic_boundaries.C

@@ -60,8 +60,7 @@ const Elem * PeriodicBoundaries::neighbor(boundary_id_type boundary_id,
                                           const PointLocatorBase & point_locator,
                                           const Elem * e,
                                           unsigned int side,
-                                          unsigned int * neigh_side,
-                                          bool skip_found_check) const
+                                          unsigned int * neigh_side) const
 {
   std::unique_ptr<const Elem> neigh_side_proxy;
 
@@ -82,9 +81,6 @@ const Elem * PeriodicBoundaries::neighbor(boundary_id_type boundary_id,
   for(const Elem * elem_it : candidate_elements)
     {
 
-      if (elem_it == e) // skip self
-        continue;
-
       std::vector<unsigned int> neigh_sides =
         mesh.get_boundary_info().sides_with_boundary_id(elem_it, b->pairedboundary);
 
@@ -106,13 +102,12 @@ const Elem * PeriodicBoundaries::neighbor(boundary_id_type boundary_id,
         }
     }
 
-  if (!skip_found_check)
-    // If we should have found a periodic neighbor but didn't then
-    // either we're on a ghosted element with a remote periodic neighbor
-    // or we're on a mesh with an inconsistent periodic boundary.
-    libmesh_error_msg_if(mesh.is_serial() ||
-                        (e->processor_id() == mesh.processor_id()),
-                        "Periodic boundary neighbor not found");
+  // If we should have found a periodic neighbor but didn't then
+  // either we're on a ghosted element with a remote periodic neighbor
+  // or we're on a mesh with an inconsistent periodic boundary.
+  libmesh_error_msg_if(mesh.is_serial() ||
+                      (e->processor_id() == mesh.processor_id()),
+                      "Periodic boundary neighbor not found");
 
   if (neigh_side)
     *neigh_side = libMesh::invalid_uint;

src/mesh/mesh_base.C

@@ -49,6 +49,10 @@
 #include <sstream>   // for std::ostringstream
 #include <unordered_map>
 
+#include "libmesh/periodic_boundaries.h"
+#include "libmesh/periodic_boundary.h"
+
+
 namespace libMesh
 {
 
@@ -1953,6 +1957,44 @@ void MeshBase::detect_interior_parents()
 
 
 
+#ifdef LIBMESH_ENABLE_PERIODIC
+  /**
+   * Register a pair of boundaries as disconnected boundaries.
+   */
+  void MeshBase::add_disconnected_boundaries(const boundary_id_type b1,
+                                  const boundary_id_type b2)
+    {
+      // Lazily allocate the container the first time it’s needed
+      if (!_disconnected_boundary_pairs)
+        _disconnected_boundary_pairs = std::make_unique<PeriodicBoundaries>();
+
+      // Create forward and inverse boundary mappings
+      PeriodicBoundary forward(RealVectorValue(0., 0., 0.));
+      PeriodicBoundary inverse(RealVectorValue(0., 0., 0.));
+
+      forward.myboundary       = b1;
+      forward.pairedboundary   = b2;
+      inverse.myboundary       = b2;
+      inverse.pairedboundary   = b1;
+
+      // Add both directions into the container
+      _disconnected_boundary_pairs->emplace(b1, forward.clone());
+      _disconnected_boundary_pairs->emplace(b2, inverse.clone());
+    }
+
+  PeriodicBoundaries * MeshBase::get_disconnected_boundaries()
+    {
+      return _disconnected_boundary_pairs.get();
+    }
+
+  const PeriodicBoundaries * MeshBase::get_disconnected_boundaries() const
+    {
+      return _disconnected_boundary_pairs.get();
+    }
+#endif
+
+
+
 void MeshBase::set_point_locator_close_to_point_tol(Real val)
 {
   _point_locator_close_to_point_tol = val;

src/mesh/unstructured_mesh.C

@@ -47,6 +47,10 @@
 #include <sstream>
 #include <unordered_map>
 
+// for disconnected neighbors
+#include "libmesh/periodic_boundaries.h"
+#include "libmesh/periodic_boundary.h"
+
 namespace {
 
 using namespace libMesh;
@@ -1015,8 +1019,11 @@ void UnstructuredMesh::find_neighbors (const bool reset_remote_elements,
 
                 for (const auto & [id, boundary_ptr] : *db)
                 {
+                  if (!this->get_boundary_info().has_boundary_id(element, ms, id))
+                    continue;
+
                   unsigned int neigh_side;
-                  const Elem * neigh = db->neighbor(id, *point_locator, element, ms, &neigh_side, true /*skip_found_check*/);
+                  const Elem * neigh = db->neighbor(id, *point_locator, element, ms, &neigh_side);
                   if (neigh && neigh != remote_elem && neigh != element)
                     {
                       element->set_neighbor(ms, this->elem_ptr(neigh->id()));

tests/systems/disconnected_neighbor_test.C

@@ -286,7 +286,7 @@ private:
     es.init();
     sys.solve();
 
-    ExodusII_IO(mesh).write_equation_systems("temperature_jump.e", es);
+    // ExodusII_IO(mesh).write_equation_systems("temperature_jump.e", es);
 
     Parameters params;