code: func checkIndexInfo(indexName string, indexColNames []*ast.IndexColName) error {
  	if strings.EqualFold(indexName, mysql.PrimaryKeyName) {
  		return ddl.ErrWrongNameForIndex.GenWithStackByArgs(indexName)
  	}
  	if len(indexColNames) > mysql.MaxKeyParts {
  		return infoschema.ErrTooManyKeyParts.GenWithStackByArgs(mysql.MaxKeyParts)
  	}
  	return checkDuplicateColumnName(indexColNames)
  }
docs: // checkIndexInfo checks index name and index column names.