Question

How devise include their generators like devise:install without the creation of lib/generator inside the rails project?

I mean, what is the magic here? Is the require_paths = ["lib"] who does the trick including the generators?

Answer 1

in the gem, there is a ‘generator’ folder structure that rails looks for

lib/generators/devise...

In devise.gemspec, the lib dir is added to the require path:

s.require_paths = ["lib"]

This means that once you add devise to your Gemfile, rails now has access to it’s generators because they follow the structure and naming conventions rails expects.

Here is the install generator for your reference. If you were to rename that file to installer_generator.rb and change the class name to InstallerGenerator, the devise install command would then become rails g devise:installer instead of rails g devise:install

Hopefully this helps clear things up.