code: func UniqueArgumentNamesRule(context *ValidationContext) *ValidationRuleInstance {
  	knownArgNames := map[string]*ast.Name{}
  
  	visitorOpts := &visitor.VisitorOptions{
  		KindFuncMap: map[string]visitor.NamedVisitFuncs{
  			kinds.Field: {
  				Kind: func(p visitor.VisitFuncParams) (string, interface{}) {
  					knownArgNames = map[string]*ast.Name{}
  					return visitor.ActionNoChange, nil
  				},
  			},
  			kinds.Directive: {
  				Kind: func(p visitor.VisitFuncParams) (string, interface{}) {
  					knownArgNames = map[string]*ast.Name{}
  					return visitor.ActionNoChange, nil
  				},
  			},
  			kinds.Argument: {
  				Kind: func(p visitor.VisitFuncParams) (string, interface{}) {
  					if node, ok := p.Node.(*ast.Argument); ok {
  						argName := ""
  						if node.Name != nil {
  							argName = node.Name.Value
  						}
  						if nameAST, ok := knownArgNames[argName]; ok {
  							reportError(
  								context,
  								fmt.Sprintf(`There can be only one argument named "%v".`, argName),
  								[]ast.Node{nameAST, node.Name},
  							)
  						} else {
  							knownArgNames[argName] = node.Name
  						}
  					}
  					return visitor.ActionSkip, nil
  				},
  			},
  		},
  	}
  	return &ValidationRuleInstance{
  		VisitorOpts: visitorOpts,
  	}
  }
docs: // UniqueArgumentNamesRule Unique argument names
  //
  // A GraphQL field or directive is only valid if all supplied arguments are
  // uniquely named.