Parameters read from JSON with SchemaXORContent could not be marshalled back - duplicate keys

[comdiv]

Have scenario

1. read _base.json as template of spec
2. update it
3. save as api.json

Got problem with parameters if they read from _base.json

1. Minimal schema to reproduce

{
   "openapi": "3.1.0",
   "paths": {
         "/": {
         "get": {
            "parameters": [
               {
                  "name": "p",
                  "schema": {
                     "type": "string"
                  },
                  "in": "query"
               }
            ]
         }
      }
   }
}

5. Read it

var spec *openapi3.Spec
if err = json.Unmarshal(errs.Must(os.ReadFile("./doc/api/_base.json")),&spec); err != nil { panic(err) }

6. Try write it back

j, err = json.MarshalIndent(spec, "", "    ")
if err != nil { panic(err) }
fmt.Println(string(j))

will produce

{
   "openapi": "3.1.0",
   "paths": {
         "/": {
         "get": {
            "parameters": [
               {
                  "name": "p",
                  "schema": {
                     "type": "string"
                  },
                  "in": "query",
                  "schema": {
                     "type": "string"
                  },
                  "in": "query"
               }
            ]
         }
      }
   }
}

7. The problem is - the combination of Parameter.SchemaXORContent,Parameter.Location and unionMarshal

SchemaXORContent is used during unmarshal as buffer, and then used back in marshalling but without any key control of
unique in unionMarhal

8. Avoid -

For our case i have added

func ReadSpecForUpdate(data []byte) (*openapi3.Spec, error) {
	var spec *openapi3.Spec
	if err := json.Unmarshal(data,&spec); err != nil { return nil, err }
	for _, path := range spec.Paths.MapOfPathItemValues {
		for _, op := range path.MapOfOperationValues {
			for _, p := range op.Parameters {
				// todo - some information could be lost ???
				p.Parameter.SchemaXORContent = nil
                                p.Parameter.Location = nil
			}
		}
	}
	return spec, nil	
}

9. Suggestion - rewrite unionMarshal - prepare data to avoid twice - pre merge data