How to use unreleased gems in a plugin?

Question

Ruby on Rails

I want to make a plugin using activeadmin on 4 rails. In the gemspec, it is not possible to specify activeadmine, since the version that does not conflict with 4 rails is still only in the master branch.
If I specify it in the gemfile, then even with an empty gemspec, it still pulls not from the github, but the latest release from rubigems gem 'activeadmin', github: 'activeadmin'. And as a result, it complains about conflicts with 4 rails.
It turned out to be an option if you do not use the gemspec plugin in the gemfile. In this case, if you go to the plugin directory and do a bundle install, then the correct versions of the gems are installed.
But if you do a bundle install from the application to which this plugin is connected, then the Gemfile is simply ignored - only what is specified in the gemspec is loaded.
Somehow I already got confused with plugins and the engine and I come to the conclusion that to use the plugin you need either huge crutches or even a temporary version of all dependencies needs to be released. But it can't be all that complicated.
Actually, the task: to create a project on 4 rails. Create a mountable plugin. This plugin should load the admin asset and create routes for it. It is assumed that the device with the user model is already loaded.

Answer 1

Try like this

gem 'activeadmin', github: 'activeadmin/activeadmin'