简单测试模板：

# app/views/test.json.jbuilder
json.attr name:

我不知道如何以其他方式访问它，但您可以在以下位置检查已编译的source：* 网址：http：github.com/rails/rails/blob/v7.0.4.3/actionview/lib/action_view/template.rb#L282*
查看模板呈现时实际运行的代码：

>> ApplicationController.renderer.render(template: "test", locals: {name: "first"})
  Rendering test.json.jbuilder
"          def _app_views_test_json_jbuilder__1585277848127427767_29960(local_assigns, output_buffer)\n            @virtual_path = \"test\";name = local_assigns[:name]; name = name;;__already_defined = defined?(json); json||=JbuilderTemplate.new(self); json.attr name:\n\n      json.target! unless (__already_defined && __already_defined != \"method\")\n          end\n"
=> TypeError # doesn't actually render

• 格式化 *

def _app_views_test_json_jbuilder__1161877154070863274_90100(local_assigns, output_buffer)
  @virtual_path = "test";               # ActionView
  name = local_assigns[:name];          # ActionView
  name = name;;                         # ActionView
  __already_defined = defined?(json);   # Jbuilder
  json||=JbuilderTemplate.new(self);    # Jbuilder
  json.attr name:                       # Your template
  json.target! unless (__already_defined && __already_defined != "method")
  #    ^ Jbuilder json output
end

如果没有方括号，json.target!将成为name的值，模板将返回json.attr返回的值或json.partial!返回的值。
如果你在这一行的末尾放一个分号，它也是可以修复的：

• 网址：http：github.com/rails/jbuilder/blob/v2.11.5/lib/jbuilder/jbuilder_template.rb#L277*

#                                                                            here v
%{__already_defined = defined?(json); json||=JbuilderTemplate.new(self); #{source};

>> ApplicationController.renderer.render(template: "test", locals: {name: "first"})
=> "{\"attr\":{\"name\":\"first\"}}"

简化版

def json *args
  @buffer = [*@buffer, *args]
end

def target 
  @buffer&.join
ensure
  @buffer = nil
end

# ^ this is action view/jbuilder
# v this is jbuilder templates

def good_template name = "first"
  json(name:)
  target
end

# same as doing:
# `json name: target`
def bad_template name = "first"
  json name:
  target
end

>> good_template
=> "{:name=>\"first\"}"
>> bad_template
=> [{:name=>nil}]       # Array instead of a String, if we had a controller
                        # there would be a TypeError somewhere.

所以method hash:仍然是一个不确定的语法，在模板中不太明显。只需使用括号：
https://bugs.ruby-lang.org/issues/18396