Prevent db:schema:load to protected environments

[jch]

Follow up to #22967 to protect against loading a schema on accident in production.

cc @schneems

[rails-bot]

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[schneems]

When loading the schema can you take destructive actions?

[jch]

@schneems when I tested locally, it blows away the existing data and creates fresh tables.

[schneems]

Can confirm

$ rails -v
riRails 5.0.0.beta3
2.3.0  /tmp
$ rails new foo
      create
      create  README.md
      create  Rakefile
      create  config.ru
      create  .gitignore
      create  Gemfile
      create  app
      create  app/assets/config/manifest.js
      create  app/assets/javascripts/application.js
      create  app/assets/javascripts/cable.coffee
      create  app/assets/stylesheets/application.css
      create  app/channels/application_cable/channel.rb
      create  app/channels/application_cable/connection.rb
      create  app/controllers/application_controller.rb
      create  app/helpers/application_helper.rb
      create  app/jobs/application_job.rb
      create  app/mailers/application_mailer.rb
      create  app/models/application_record.rb
      create  app/views/layouts/application.html.erb
      create  app/views/layouts/mailer.html.erb
      create  app/views/layouts/mailer.text.erb
      create  app/assets/images/.keep
      create  app/assets/javascripts/channels
      create  app/assets/javascripts/channels/.keep
      create  app/controllers/concerns/.keep
      create  app/models/concerns/.keep
      create  bin
      create  bin/bundle
      create  bin/rails
      create  bin/rake
      create  bin/setup
      create  bin/update
      create  config
      create  config/routes.rb
      create  config/application.rb
      create  config/environment.rb
      create  config/secrets.yml
      create  config/cable.yml
      create  config/puma.rb
      create  config/environments
      create  config/environments/development.rb
      create  config/environments/production.rb
      create  config/environments/test.rb
      create  config/initializers
      create  config/initializers/active_record_belongs_to_required_by_default.rb
      create  config/initializers/application_controller_renderer.rb
      create  config/initializers/assets.rb
      create  config/initializers/backtrace_silencers.rb
      create  config/initializers/callback_terminator.rb
      create  config/initializers/cookies_serializer.rb
      create  config/initializers/cors.rb
      create  config/initializers/filter_parameter_logging.rb
      create  config/initializers/inflections.rb
      create  config/initializers/mime_types.rb
      create  config/initializers/per_form_csrf_tokens.rb
      create  config/initializers/request_forgery_protection.rb
      create  config/initializers/session_store.rb
      create  config/initializers/wrap_parameters.rb
      create  config/locales
      create  config/locales/en.yml
      create  config/boot.rb
      create  config/database.yml
      create  db
      create  db/seeds.rb
      create  lib
      create  lib/tasks
      create  lib/tasks/.keep
      create  lib/assets
      create  lib/assets/.keep
      create  log
      create  log/.keep
      create  public
      create  public/404.html
      create  public/422.html
      create  public/500.html
      create  public/apple-touch-icon-precomposed.png
      create  public/apple-touch-icon.png
      create  public/favicon.ico
      create  public/robots.txt
      create  test/fixtures
      create  test/fixtures/.keep
      create  test/fixtures/files
      create  test/fixtures/files/.keep
      create  test/controllers
      create  test/controllers/.keep
      create  test/mailers
      create  test/mailers/.keep
      create  test/models
      create  test/models/.keep
      create  test/helpers
      create  test/helpers/.keep
      create  test/integration
      create  test/integration/.keep
      create  test/test_helper.rb
      create  tmp
      create  tmp/.keep
      create  tmp/cache
      create  tmp/cache/assets
      create  vendor/assets/javascripts
      create  vendor/assets/javascripts/.keep
      create  vendor/assets/stylesheets
      create  vendor/assets/stylesheets/.keep
      remove  config/initializers/cors.rb
         run  bundle install
cd foo
Fetching gem metadata from https://rubygems.org/..rails. ...g .mi.g...r
Fetching version metadata from https://rubygems.org/.ation add..
Fetching dependency metadata from https://rubygems.org/..
Resolving dependencies..............
Using concurrent-ruby 1.0.1
Using i18n 0.7.0
Using minitest 5.8.4
Using thread_safe 0.3.5
Using builder 3.2.2
Using erubis 2.7.0
Using mini_portile2 2.0.0
Using json 1.8.3
Using nio4r 1.2.1
Using websocket-extensions 0.1.2
Using mime-types-data 3.2016.0221
Using arel 7.0.0
Using bundler 1.11.2
Using byebug 8.2.2
Using coffee-script-source 1.10.0
Using execjs 2.6.0
Using method_source 0.8.2
Using thor 0.19.1
Using debug_inspector 0.0.2
Using ffi 1.9.10
Using multi_json 1.11.2
Using rb-fsevent 0.9.7
Installing rake 11.1.2
Installing puma 3.3.0 with native extensions
Installing sass 3.4.22
Using tilt 2.0.2
Using spring 1.6.4
Using sqlite3 1.3.11
Installing turbolinks-source 5.0.0.beta4
Using tzinfo 1.2.2
Using nokogiri 1.6.7.2
Using rack 2.0.0.alpha
Using websocket-driver 0.6.3
Using mime-types 3.0
Using coffee-script 2.4.1
Installing uglifier 3.0.0
Using rb-inotify 0.9.7
Using turbolinks 5.0.0.beta2
Using activesupport 5.0.0.beta3
Using loofah 2.0.3
Using rack-test 0.6.3
Using sprockets 3.5.2
Using mail 2.6.4
Using listen 3.0.6
Using rails-deprecated_sanitizer 1.0.3
Using globalid 0.3.6
Using activemodel 5.0.0.beta3
Using jbuilder 2.4.1
Using rails-html-sanitizer 1.0.3
Using spring-watcher-listen 2.0.0
Using rails-dom-testing 1.0.7
Using activejob 5.0.0.beta3
Using activerecord 5.0.0.beta3
Using actionview 5.0.0.beta3
Using actionpack 5.0.0.beta3
Using actioncable 5.0.0.beta3
Using actionmailer 5.0.0.beta3
Using railties 5.0.0.beta3
Using sprockets-rails 3.0.4
Using coffee-rails 4.1.1
Using jquery-rails 4.1.1
Using web-console 3.1.1
Using rails 5.0.0.beta3
Using sass-rails 5.0.4
Bundle complete! 15 Gemfile dependencies, 64 gems now installed.
Use `bundle show [gemname]` to see where a bundled gem is installed.
         run  bundle exec spring binstub --all
* bin/rake: spring inserted
* bin/rails: spring inserted
2.3.0  /tmp
$ cd foo
2.3.0  /tmp/foo
$ rails g scaffold user name email
      invoke  active_record
      create    db/migrate/20160406173152_create_users.rb
      create    app/models/user.rb
      invoke    test_unit
      create      test/models/user_test.rb
      create      test/fixtures/users.yml
      invoke  resource_route
       route    resources :users
      invoke  scaffold_controller
      create    app/controllers/users_controller.rb
      invoke    erb
      create      app/views/users
      create      app/views/users/index.html.erb
      create      app/views/users/edit.html.erb
      create      app/views/users/show.html.erb
      create      app/views/users/new.html.erb
      create      app/views/users/_form.html.erb
      invoke    test_unit
      create      test/controllers/users_controller_test.rb
      invoke    helper
      create      app/helpers/users_helper.rb
      invoke      test_unit
      invoke    jbuilder
      create      app/views/users/index.json.jbuilder
      create      app/views/users/show.json.jbuilder
      invoke  assets
      invoke    coffee
      create      app/assets/javascripts/users.coffee
      invoke    scss
      create      app/assets/stylesheets/users.scss
      invoke  scss
      create    app/assets/stylesheets/scaffolds.scss
2.3.0  /tmp/foo
$ rake db:migrate
rails console
== 20160406173152 CreateUsers: migrating ======================================
-- create_table(:users)
   -> 0.0013s
== 20160406173152 CreateUsers: migrated (0.0014s) =============================

2.3.0  /tmp/foo
$ rails console
User.newLoading development environment (Rails 5.0.0.beta3)
irb(main):001:0> User.new(name: 'schneems').save
   (0.0ms)  begin transaction
  SQL (0.4ms)  INSERT INTO "users" ("name", "created_at", "updated_at") VALUES (?, ?, ?)  [["name", "schneems"], ["created_at", 2016-04-06 17:32:08 UTC], ["updated_at", 2016-04-06 17:32:08 UTC]]
   (0.8ms)  commit transaction
=> true
irb(main):002:0> User.count
   (0.2ms)  SELECT COUNT(*) FROM "users"
=> 1
irb(main):003:0> exit
2.3.0  /tmp/foo
$ rake db:schema:load
-- create_table("users", {:force=>:cascade})
   -> 0.0263s
-- initialize_schema_migrations_table()
   -> 0.0039s
-- create_table("users", {:force=>:cascade})
   -> 0.0025s
-- initialize_schema_migrations_table()
   -> 0.0016s
2.3.0  /tmp/foo
$ rails c
Loading development environment (Rails 5.0.0.beta3)
irb(main):001:0> User.count
   (0.1ms)  SELECT COUNT(*) FROM "users"
=> 0

[schneems]

Thanks for the PR!