Add spec lookup in the attached spec array using the compiler option pointer.

This enables to find the spec associated with the compiler option stored in the objects, which do not necessarily belong to the model that owns them.

PiperOrigin-RevId: 713259419
Change-Id: I579c770147ff07ed2a5edd20e7a795ee7cc27147

src/user/user_model.h

@@ -236,6 +236,7 @@ class mjCModel : public mjCModel_, private mjSpec {
   mjCBase* FindObject(mjtObj type, std::string name) const;         // find object given type and name
   mjCBase* FindTree(mjCBody* body, mjtObj type, std::string name);  // find tree object given name
   mjSpec* FindSpec(std::string name) const;                         // find spec given name
+  mjSpec* FindSpec(const mjsCompiler* compiler_) const;             // find spec given mjsCompiler
   void ActivatePlugin(const mjpPlugin* plugin, int slot);           // activate plugin
 
   // accessors
@@ -303,10 +304,16 @@ class mjCModel : public mjCModel_, private mjSpec {
   // map from default class name to default class pointer
   std::unordered_map<std::string, mjCDef*> def_map;
 
+  // get the spec from which this model was created
+  mjSpec* GetSourceSpec() const;
+
  private:
   // settings for each defaults class
   std::vector<mjCDef*> defaults_;
 
+  // spec from which this model was created in copy constructor
+  mjSpec* source_spec_;
+
   // list of active plugins
   std::vector<std::pair<const mjpPlugin*, int>> active_plugins_;