Python bindings: Store a reference to MjModel in MjDataWrapper.

Before this change, MjDataWrapper contained a custom data structure called MjDataMetadata, which contained the sizes of various arrays needed to create MjData. This was used for serialization and deserialization, as well as copying MjData instances.

This worked fine for native MuJoCo models, but as soon as plugins were used, there was information in the model that was needed and not available in MjDataMetadata. Since plugins are so general, keeping MjDataMetadata was untenable.

PiperOrigin-RevId: 578205355
Change-Id: I11b9ee797d1da5aaf1fecbbe170b3b0f1f1a3e6c

python/mujoco/indexers.h

@@ -25,7 +25,6 @@
 #include <absl/container/flat_hash_map.h>
 #include <mujoco/mjxmacro.h>
 #include "indexer_xmacro.h"
-#include "mjdata_meta.h"
 #include "raw.h"
 #include <pybind11/numpy.h>
 #include <pybind11/pybind11.h>
@@ -35,9 +34,7 @@ using NameToID = absl::flat_hash_map<std::string, int>;
 using IDToName = std::vector<std::string>;
 
 struct NameToIDMappings {
-  // M is either a raw::MjModel or MjDataMetadata.
-  template <typename M>
-  explicit NameToIDMappings(const M& m);
+  explicit NameToIDMappings(const raw::MjModel& m);
 
   NameToID body;
   NameToID jnt;
@@ -63,9 +60,7 @@ struct NameToIDMappings {
 };
 
 struct IDToNameMappings {
-  // M is either a raw::MjModel or MjDataMetadata.
-  template <typename M>
-  explicit IDToNameMappings(const M& m);
+  explicit IDToNameMappings(const raw::MjModel& m);
 
   IDToName body;
   IDToName jnt;
@@ -163,7 +158,7 @@ class MjModelIndexer {
 class MjDataGroupedViewsBase {
  public:
   MjDataGroupedViewsBase(int index, std::string_view name, raw::MjData* d,
-                         const MjDataMetadata* m,
+                         const raw::MjModel* m,
                          pybind11::handle owner)
       : index_(index), name_(name), d_(d), m_(m), owner_(owner) {}
 
@@ -175,7 +170,7 @@ class MjDataGroupedViewsBase {
   int index_;
   std::string name_;
   raw::MjData* d_;
-  const MjDataMetadata* m_;
+  const raw::MjModel* m_;
   pybind11::handle owner_;
 };
 
@@ -201,7 +196,7 @@ MJDATA_VIEW_GROUPS
 // (e.g. a particular geom or joint) either by name or by ID.
 class MjDataIndexer {
  public:
-  MjDataIndexer(raw::MjData* d, const MjDataMetadata* m,
+  MjDataIndexer(raw::MjData* d, const raw::MjModel* m,
                 pybind11::handle owner);
 
 #define XGROUP(MjDataGroupedViews, field, nfield, FIELD_XMACROS) \
@@ -213,7 +208,7 @@ class MjDataIndexer {
 
  private:
   raw::MjData* d_;
-  const MjDataMetadata* m_;
+  const raw::MjModel* m_;
   pybind11::handle owner_;
   NameToIDMappings name_to_id_;
   IDToNameMappings id_to_name_;