Verify PointLocator validity

include/utils/point_locator_base.h

@@ -196,6 +196,35 @@ class PointLocatorBase : public ReferenceCountedObject<PointLocatorBase>
    */
   const MeshBase & get_mesh() const;
 
+  /**
+   * Get the verbosity setting (whether to print extra info to screen,
+   * default false) for this PointLocator
+   */
+  bool get_verbose() const { return _verbose; }
+
+  /**
+   * Set the verbosity setting for this PointLocator
+   */
+  void set_verbose(bool verbosity) { _verbose = verbosity; }
+
+#ifndef NDEBUG
+  /**
+   * Verifies that, for every node of every element, the point locator
+   * finds that element when searching at that node.  This is an
+   * O(N log N) operation, and so only available in builds with NDEBUG
+   * undefined, for asserting internal consistency (the PointLocator
+   * works) and external consistency (user code didn't change the mesh
+   * without updating the PointLocator afterward) that we hope should
+   * never be broken in opt.
+   */
+  void libmesh_assert_valid_point_locator ();
+#endif
+
+
+#ifndef LIBMESH_ENABLE_DEPRECATED
+protected:
+#endif
+
   /**
    * Boolean flag to indicate whether to print out extra info.
    */

src/utils/point_locator_base.C

@@ -22,6 +22,7 @@
 #include "libmesh/point_locator_tree.h"
 #include "libmesh/elem.h"
 #include "libmesh/enum_point_locator_type.h"
+#include "libmesh/mesh_base.h"
 #include "libmesh/point_locator_nanoflann.h"
 
 namespace libMesh
@@ -153,4 +154,29 @@ locate_node(const Point & p,
   return nullptr;
 }
 
+
+#ifndef NDEBUG
+void PointLocatorBase::libmesh_assert_valid_point_locator ()
+{
+  // We might only have been built with TREE_LOCAL_ELEMENTS as an
+  // option; let's just check local elements to be safe.
+  for (const Elem * elem : this->_mesh.active_local_element_ptr_range())
+    {
+      // For non-Lagrange mappings, we might have nodes that are
+      // really control points, not contained in the element they
+      // define; we can only safely check containment of vertices.
+      auto range = make_range(0u, (elem->mapping_type() == LAGRANGE_MAP) ?
+                                 elem->n_nodes() : elem->n_vertices());
+
+        for (auto n : range)
+          {
+            const Node & node = elem->node_ref(n);
+            std::set<const Elem *> candidate_elements;
+            this->operator()(node, candidate_elements);
+            libmesh_assert(candidate_elements.count(elem));
+          }
+    }
+}
+#endif
+
 } // namespace libMesh

src/utils/point_locator_tree.C

@@ -175,6 +175,10 @@ void PointLocatorTree::init (Trees::BuildType build_type)
 
   // ready for take-off
   this->_initialized = true;
+
+  // This may be too expensive to use even in debug mode, but it's
+  // helpful to uncomment for debugging.
+  // this->libmesh_assert_valid_point_locator();
 }
 
 const Elem * PointLocatorTree::operator() (const Point & p,