Creating a new Rails app using locally checked-out code.

rails_new_dev.sh

# Fork rails/rails on Github
> git clone gem https://github.com/thomascountz/rails.git
Cloning into 'rails'...

> cd rails

# Checkout SHA prior to the merge commit and create a new branch
> git checkout -b practice-pr-46683 59fe981^
Switched to a new branch 'practice-pr-46683'

> bundle install

# Create a new Rails app using the checked-out code
> bundle exec rails new ../test_app --dev
...
Using activerecord 7.1.0.alpha from source at `/Users/thomas.countz/Code/rails`
...