Is this gem compatible with Rails 4.x, Ruby 2.x?

The README says: ActionMailerWithRequest >= 0.3 requires Rails 3. Use TabsOnRails 0.2.x with Rails 2.

I'm not sure how TabsOnRails is related, but it doesn't seem to contain any ActionMailer code. There is also not a actionmailer-with-request gem version 0.2.x listed here https://rubygems.org/gems/actionmailer-with-request

Is there a version which works with Rails 2?

I don't use ActionMailer so I won't make a pull request myself, but I answered a question on SO and recommended your gem as it sounds like a solution to the problem (http://stackoverflow.com/questions/29658271/rails-request-url-getting-undefined-local-variable-in-mailer/29699048#29699048).

I just looked at the sources and found that you're using Thread.current to store the request. You should maybe use RequestStore or something similar if available, because Thread.current may not give you the value you want with e.g. Puma, or more likely, you'll get a value when you don't expect one.

Example: https://github.com/Aethelflaed/mongoid-userstamps/blob/master/lib/mongoid/userstamps/config.rb#L65

Using this gem with Rails 5 throw a deprecation warnings:

# before_filter => before_action
DEPRECATION WARNING: before_filter is deprecated and will be removed in Rails 5.1. 
Use before_action instead.

# alias_method_chain => Module#prepend
DEPRECATION WARNING: alias_method_chain is deprecated. Please, use Module#prepend instead.
From module, you can access the original method using super.

I'm getting

`load_missing_constant': uninitialized constant ActionMailerWithRequest::MailerMonkeyPatch (NameError)

when running on my config rails 2.3.5 ruby 1.8.7. Is there Rails 3 required ?

i found this as a gem on rubygems, however i can only get it to work as a plugin.

is the gem an older version?