From 811e08e3e94d8646d9c7731e311b5f80f18416cf Mon Sep 17 00:00:00 2001
From: jdolence <jcdolence@gmail.com>
Date: Tue, 15 Aug 2023 13:21:16 -0600
Subject: [PATCH] add default descriptors/sparse packs for weird usage
 downstream

---
 src/amr_criteria/amr_criteria.hpp      | 1 -
 src/interface/make_pack_descriptor.hpp | 2 ++
 src/interface/sparse_pack.hpp          | 1 +
 src/interface/sparse_pack_base.hpp     | 5 +++++
 4 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/amr_criteria/amr_criteria.hpp b/src/amr_criteria/amr_criteria.hpp
index 86b09c9728a1..e31bd8b381d8 100644
--- a/src/amr_criteria/amr_criteria.hpp
+++ b/src/amr_criteria/amr_criteria.hpp
@@ -17,7 +17,6 @@
 #include <string>
 
 #include "defs.hpp"
-//#include "interface/meshblock_data.hpp"
 #include "mesh/domain.hpp"
 
 namespace parthenon {
diff --git a/src/interface/make_pack_descriptor.hpp b/src/interface/make_pack_descriptor.hpp
index bd838e37363f..f3cfe17ec4f3 100644
--- a/src/interface/make_pack_descriptor.hpp
+++ b/src/interface/make_pack_descriptor.hpp
@@ -36,6 +36,8 @@
 
 namespace parthenon {
 
+inline auto MakeDefaultPackDescriptor() { return typename SparsePack<>::Descriptor(); }
+
 inline auto MakePackDescriptor(StateDescriptor *psd, const std::vector<std::string> &vars,
                                const std::vector<bool> &use_regex,
                                const std::vector<MetadataFlag> &flags = {},
diff --git a/src/interface/sparse_pack.hpp b/src/interface/sparse_pack.hpp
index 4b646abc0793..ef21ee16fa98 100644
--- a/src/interface/sparse_pack.hpp
+++ b/src/interface/sparse_pack.hpp
@@ -122,6 +122,7 @@ class SparsePack : public SparsePackBase {
 
   class Descriptor : public impl::PackDescriptor {
    public:
+    Descriptor() = default;
     explicit Descriptor(const impl::PackDescriptor &desc_in)
         : impl::PackDescriptor(desc_in) {}
 
diff --git a/src/interface/sparse_pack_base.hpp b/src/interface/sparse_pack_base.hpp
index 732862e307d9..97c95995c8ac 100644
--- a/src/interface/sparse_pack_base.hpp
+++ b/src/interface/sparse_pack_base.hpp
@@ -127,6 +127,11 @@ struct PackDescriptor {
 
   void Print() const;
 
+  // default constructor needed for certain use cases
+  PackDescriptor()
+      : nvar_groups(0), var_group_names({}), var_groups({}), with_fluxes(false),
+        coarse(false), flat(false) {}
+
   template <class GROUP_t, class SELECTOR_t>
   PackDescriptor(StateDescriptor *psd, const std::vector<GROUP_t> &var_groups_in,
                  const SELECTOR_t &selector, const std::set<PDOpt> &options)