Fix field ordering in mjModel.

`nnames_map` is not required for `mjModel` construction, it is set during construction.

PiperOrigin-RevId: 696462793
Change-Id: Ie722e2a04d7fd7ed96634d3304cc94e895ed713b

doc/includes/references.h

@@ -948,10 +948,10 @@ struct mjModel_ {
   int nuser_actuator;             // number of mjtNums in actuator_user
   int nuser_sensor;               // number of mjtNums in sensor_user
   int nnames;                     // number of chars in all names
-  int nnames_map;                 // number of slots in the names hash map
   int npaths;                     // number of chars in all paths
 
-  // sizes set after mjModel construction (only affect mjData)
+  // sizes set after mjModel construction
+  int nnames_map;                 // number of slots in the names hash map
   int nM;                         // number of non-zeros in sparse inertia matrix
   int nB;                         // number of non-zeros in sparse body-dof matrix
   int nC;                         // number of non-zeros in sparse reduced dof-dof matrix
@@ -959,8 +959,8 @@ struct mjModel_ {
   int ntree;                      // number of kinematic trees under world body
   int ngravcomp;                  // number of bodies with nonzero gravcomp
   int nemax;                      // number of potential equality-constraint rows
-  int njmax;                      // number of available rows in constraint Jacobian
-  int nconmax;                    // number of potential contacts in contact list
+  int njmax;                      // number of available rows in constraint Jacobian (legacy)
+  int nconmax;                    // number of potential contacts in contact list (legacy)
   int nuserdata;                  // number of mjtNums reserved for the user
   int nsensordata;                // number of mjtNums in sensor data vector
   int npluginstate;               // number of mjtNums in plugin state vector

include/mujoco/mjmodel.h

@@ -655,10 +655,10 @@ struct mjModel_ {
   int nuser_actuator;             // number of mjtNums in actuator_user
   int nuser_sensor;               // number of mjtNums in sensor_user
   int nnames;                     // number of chars in all names
-  int nnames_map;                 // number of slots in the names hash map
   int npaths;                     // number of chars in all paths
 
-  // sizes set after mjModel construction (only affect mjData)
+  // sizes set after mjModel construction
+  int nnames_map;                 // number of slots in the names hash map
   int nM;                         // number of non-zeros in sparse inertia matrix
   int nB;                         // number of non-zeros in sparse body-dof matrix
   int nC;                         // number of non-zeros in sparse reduced dof-dof matrix
@@ -666,8 +666,8 @@ struct mjModel_ {
   int ntree;                      // number of kinematic trees under world body
   int ngravcomp;                  // number of bodies with nonzero gravcomp
   int nemax;                      // number of potential equality-constraint rows
-  int njmax;                      // number of available rows in constraint Jacobian
-  int nconmax;                    // number of potential contacts in contact list
+  int njmax;                      // number of available rows in constraint Jacobian (legacy)
+  int nconmax;                    // number of potential contacts in contact list (legacy)
   int nuserdata;                  // number of mjtNums reserved for the user
   int nsensordata;                // number of mjtNums in sensor data vector
   int npluginstate;               // number of mjtNums in plugin state vector

introspect/structs.py

@@ -1148,16 +1148,16 @@ STRUCTS: Mapping[str, StructDecl] = dict([
                  type=ValueType(name='int'),
                  doc='number of chars in all names',
              ),
-             StructFieldDecl(
-                 name='nnames_map',
-                 type=ValueType(name='int'),
-                 doc='number of slots in the names hash map',
-             ),
              StructFieldDecl(
                  name='npaths',
                  type=ValueType(name='int'),
                  doc='number of chars in all paths',
              ),
+             StructFieldDecl(
+                 name='nnames_map',
+                 type=ValueType(name='int'),
+                 doc='number of slots in the names hash map',
+             ),
              StructFieldDecl(
                  name='nM',
                  type=ValueType(name='int'),
@@ -1196,12 +1196,12 @@ STRUCTS: Mapping[str, StructDecl] = dict([
              StructFieldDecl(
                  name='njmax',
                  type=ValueType(name='int'),
-                 doc='number of available rows in constraint Jacobian',
+                 doc='number of available rows in constraint Jacobian (legacy)',
              ),
              StructFieldDecl(
                  name='nconmax',
                  type=ValueType(name='int'),
-                 doc='number of potential contacts in contact list',
+                 doc='number of potential contacts in contact list (legacy)',
              ),
              StructFieldDecl(
                  name='nuserdata',

unity/Runtime/Bindings/MjBindings.cs

@@ -5238,8 +5238,8 @@ public unsafe struct mjModel_ {
   public int nuser_actuator;
   public int nuser_sensor;
   public int nnames;
-  public int nnames_map;
   public int npaths;
+  public int nnames_map;
   public int nM;
   public int nB;
   public int nC;