Allow use of instance variables for custom Error classes in Rails/HelperInstanceVariable

[januszm]

Is your feature request related to a problem? Please describe.

When I use a custom Error class in a helper method using a variable, it gets flagged by Rails/HelperInstanceVariable.

Describe the solution you'd like

I'd like Rails/HelperInstanceVariable to accept assignment to instance variables for use with a custom Error class:

module SomeHelper
  class InvalidSomethingError < StandardError
    attr_reader :foo

    def initialize(messsage = nil, foo: nil)
      super(message)
      @foo = foo
    end

    def message
      klass = foo.is_a?(Class) ? foo : foo.class
      "#{klass} is not supported!"
    end
  end

  # def helper methods that use InvalidSomethingError
end

Similar to: #311

[koic]

I'm wondering if it makes sense for exception classes to be placed in helpers where view helper is placed. Probably it will be placed in a place such as models or controllers.

[januszm]

Depends, custom error classes are often, defined where they belong, eg in a service class or other that is not a model or controller. I have a use case where I only need this error inside helpers but I won't insist 😉