Adds strong_migrations gem. Closes #214 (#281)

Have tested this different variants, and all of the existing default
migrations pass without errors.

---------

Co-authored-by: Dave Park <david.park@ackama.com>
Co-authored-by: Eoin Kelly <eoin.kelly@ackama.com>

Author: 3 people

template.rb

@@ -110,7 +110,7 @@ def apply_template! # rubocop:disable Metrics/MethodLength, Metrics/AbcSize, Met
   # The block passed to "after_bundle" seems to run after `bundle install`
   # but also after `shakapacker:install` and after Rails has initialized the git
   # repo
-  after_bundle do
+  after_bundle do # rubocop:disable Metrics/BlockLength
     # Remove the `test/` directory because we always use RSpec which creates
     # its own `spec/` directory
     remove_dir "test"
@@ -193,6 +193,13 @@ def apply_template! # rubocop:disable Metrics/MethodLength, Metrics/AbcSize, Met
     git add: "-A ."
     git commit: "-n -m 'Set up erblint'"
 
+    # Run strong_migrations generator near the end so that it doesn't block
+    # other parts of the template from creating migrations.
+    run_with_clean_bundler_env "bundle exec rails g strong_migrations:install"
+    run_with_clean_bundler_env "bundle exec rubocop -A -c ./.rubocop.yml"
+    git add: "-A ."
+    git commit: "-n -m 'Set up strong_migrations'"
+
     # Run the README template at the end because it introspects the app to
     # discover rake tasks etc.
     apply_readme_template

variants/backend-base/Gemfile.tt

@@ -35,6 +35,9 @@ gem "stimulus-rails"
 # Use Active Storage variants [https://guides.rubyonrails.org/active_storage_overview.html#transforming-images]
 # gem "image_processing", "~> 1.2"
 
+# Protect against accidentally slow migrations
+gem "strong_migrations"
+
 group :development do
   gem "letter_opener"
 

variants/frontend-base/template.rb

@@ -25,7 +25,6 @@
 # Configure app/frontend
 
 run "mv app/javascript app/frontend"
-
 copy_file "config/webpack/webpack.config.js", force: true
 
 gsub_file "config/shakapacker.yml", "source_entry_path: /", "source_entry_path: packs", force: true