Rails generate isn't working in the development of a Gem - ruby-on-rails

Question

I'm building a small Gem at the moment, and I'd like to be able to use Rails G for certain things, but every time I do, I get the same (long) response
I thought it was possible to use Rails G despite not actually working in the rails environment when building a gem?
Here's the response:
Usage:
rails new APP_PATH [options]
Options:
-r, [--ruby=PATH] # Path to the Ruby binary of your choice
# Default: /Users/David/.rvm/rubies/ruby-2.3.0/bin/ruby
-m, [--template=TEMPLATE] # Path to some application template (can be a filesystem path or URL)
-d, [--database=DATABASE] # Preconfigure for selected database (options: mysql/postgresql/sqlite3/oracle/frontbase/ibm_db/sqlserver/jdbcmysql/jdbcsqlite3/jdbcpostgresql/jdbc)
# Default: sqlite3
[--webpack=WEBPACK] # Preconfigure for app-like JavaScript with Webpack (options: react/vue/angular)
[--skip-yarn], [--no-skip-yarn] # Don't use Yarn for managing JavaScript dependencies
[--skip-gemfile], [--no-skip-gemfile] # Don't create a Gemfile
-G, [--skip-git], [--no-skip-git] # Skip .gitignore file
[--skip-keeps], [--no-skip-keeps] # Skip source control .keep files
-M, [--skip-action-mailer], [--no-skip-action-mailer] # Skip Action Mailer files
-O, [--skip-active-record], [--no-skip-active-record] # Skip Active Record files
-P, [--skip-puma], [--no-skip-puma] # Skip Puma related files
-C, [--skip-action-cable], [--no-skip-action-cable] # Skip Action Cable files
-S, [--skip-sprockets], [--no-skip-sprockets] # Skip Sprockets files
[--skip-spring], [--no-skip-spring] # Don't install Spring application preloader
[--skip-listen], [--no-skip-listen] # Don't generate configuration that depends on the listen gem
[--skip-coffee], [--no-skip-coffee] # Don't use CoffeeScript
-J, [--skip-javascript], [--no-skip-javascript] # Skip JavaScript files
[--skip-turbolinks], [--no-skip-turbolinks] # Skip turbolinks gem
-T, [--skip-test], [--no-skip-test] # Skip test files
[--skip-system-test], [--no-skip-system-test] # Skip system test files
[--dev], [--no-dev] # Setup the application with Gemfile pointing to your Rails checkout
[--edge], [--no-edge] # Setup the application with Gemfile pointing to Rails repository
[--rc=RC] # Path to file containing extra configuration options for rails command
[--no-rc], [--no-no-rc] # Skip loading of extra configuration options from .railsrc file
[--api], [--no-api] # Preconfigure smaller stack for API only apps
-B, [--skip-bundle], [--no-skip-bundle] # Don't run bundle install
Runtime options:
-f, [--force] # Overwrite files that already exist
-p, [--pretend], [--no-pretend] # Run but do not make any changes
-q, [--quiet], [--no-quiet] # Suppress status output
-s, [--skip], [--no-skip] # Skip files that already exist
Rails options:
-h, [--help], [--no-help] # Show this help message and quit
-v, [--version], [--no-version] # Show Rails version number and quit
Description:
The 'rails new' command creates a new Rails application with a default
directory structure and configuration at the path you specify.
You can specify extra command-line arguments to be used every time
'rails new' runs in the .railsrc configuration file in your home directory.
Note that the arguments specified in the .railsrc file don't affect the
defaults values shown above in this help message.
Example:
rails new ~/Code/Ruby/weblog
This generates a skeletal Rails installation in ~/Code/Ruby/weblog.

Answer 1

set separate .ruby-version and .ruby-gemset file
install rails gem and bundler gem.
You can use the generators which are available for non rails app.