Small Bugfix: Remove shared_ptr cycle in Tree

CHANGELOG.md

@@ -26,6 +26,7 @@
 - [[PR 1004]](https://github.com/parthenon-hpc-lab/parthenon/pull/1004) Allow parameter modification from an input file for restarts
 
 ### Fixed (not changing behavior/API/variables/...)
+- [[PR 1112]](https://github.com/parthenon-hpc-lab/parthenon/pull/1112) Remove shared_ptr cycle in forest::Tree
 - [[PR 1104]](https://github.com/parthenon-hpc-lab/parthenon/pull/1104) Fix reading restarts due to hidden ghost var
 - [[PR 1098]](https://github.com/parthenon-hpc-lab/parthenon/pull/1098) Move to symmetrized logical coordinates and fix SMR bug
 - [[PR 1095]](https://github.com/parthenon-hpc-lab/parthenon/pull/1095) Add missing include guards in hdf5 restart

src/mesh/forest/tree.cpp

@@ -323,7 +323,7 @@ Tree::GetBlockBCs(const LogicalLocation &loc) const {
 void Tree::AddNeighborTree(CellCentOffsets offset, std::shared_ptr<Tree> neighbor_tree,
                            RelativeOrientation orient, const bool periodic) {
   int location_idx = offset.GetIdx();
-  neighbors[location_idx].insert({neighbor_tree, orient});
+  neighbors[location_idx].insert({neighbor_tree.get(), orient});
   BoundaryFace fidx = offset.Face();
 
   if (fidx >= 0)

src/mesh/forest/tree.hpp

@@ -54,7 +54,7 @@ class Tree : public std::enable_shared_from_this<Tree> {
     RelativeOrientation orient;
     orient.use_offset = true;
     orient.offset = {0, 0, 0};
-    ptree->neighbors[13].insert({ptree, orient});
+    ptree->neighbors[13].insert({ptree.get(), orient});
     return ptree;
   }
 
@@ -117,8 +117,7 @@ class Tree : public std::enable_shared_from_this<Tree> {
   // multiple neighbors generally, we keep a map at each neighbor location from
   // the tree sptr to the relative logical coordinate orientation of the neighbor
   // block.
-  std::array<std::unordered_map<std::shared_ptr<Tree>, RelativeOrientation>, 27>
-      neighbors;
+  std::array<std::unordered_map<Tree *, RelativeOrientation>, 27> neighbors;
 
   std::array<BoundaryFlag, BOUNDARY_NFACES> boundary_conditions;