*   Created rake restart task. Restarts your Rails app by touching the 
    `tmp/restart.txt`.

    Fixes #18876.

    *Hyonjee Joo*

*   Set Rails console to use log formatter and log level as specified for the
    given environment.

    Fixes #15470.

    *Jacob Evelyn*

*   Add `config/initializers/active_record_belongs_to_required_by_default.rb`

    Newly generated Rails apps have a new initializer called
    `active_record_belongs_to_required_by_default.rb` which sets the value of
    the configuration option `config.active_record.belongs_to_requred_by_default`
    to `true` when ActiveRecord is not skipped.

    As a result, new Rails apps require `belongs_to` association on model
    to be valid.

    This initializer is *not* added when running `rake rails:update`, so
    old apps ported to Rails 5 will work without any change.

    *Josef Šimánek*

*   `delete` operations in configurations are run last in order to eliminate
    'No such middleware' errors when `insert_before` or `insert_after` are added
    after the `delete` operation for the middleware being deleted.

    Fixes: #16433.

    *Guo Xiang Tan*

*   Newly generated applications get a `README.md` in Markdown.

    *Xavier Noria*

*   Remove the documentation tasks `doc:app`, `doc:rails`, and `doc:guides`.

    *Xavier Noria*

*   Force generated routes to be inserted into routes.rb

    *Andrew White*

*   Don't remove all line endings from routes.rb when revoking scaffold.

    Fixes #15913.

    *Andrew White*

*   Rename `--skip-test-unit` option to `--skip-test` in app generator

    *Melanie Gilman*

*   Add the `method_source` gem to the default Gemfile for apps

    *Sean Griffin*

*   Drop old test locations from `rake stats`
    - test/functional
    - test/unit

    *Ravil Bayramgalin*

*   Update `rake stats` to  correctly count declarative tests
    as methods in `_test.rb` files.

    *Ravil Bayramgalin*

*   Remove deprecated `test:all` and `test:all:db` tasks.

    *Rafael Mendonça França*

*   Remove deprecated `Rails::Rack::LogTailer`.

    *Rafael Mendonça França*

*   Remove deprecated `RAILS_CACHE` constant.

    *Rafael Mendonça França*

*   Remove deprecated `serve_static_assets` configuration.

    *Rafael Mendonça França*

*   Use local variables in `_form.html.erb` partial generated by scaffold.

    *Andrew Kozlov*

*   Add `config/initializers/callback_terminator.rb`

    Newly generated Rails apps have a new initializer called
    `callback_terminator.rb` which sets the value of the configuration option
    `config.active_support.halt_callback_chains_on_return_false` to `false`.

    As a result, new Rails apps do not halt callback chains when a callback
    returns `false`; only when they are explicitly halted with `throw(:abort)`.

    The terminator is *not* added when running `rake rails:update`, so returning
    `false` will still work on old apps ported to Rails 5, displaying a
    deprecation warning to prompt users to update their code to the new syntax.

    *claudiob*

*   Generated fixtures won't use the id when generated with references attributes.

    *Pablo Olmos de Aguilera Corradini*

*   Add `--skip-action-mailer` option to the app generator.

    *claudiob*

*   Autoload any second level directories called `app/*/concerns`.

    *Alex Robbin*

Please check [4-2-stable](https://github.com/rails/rails/blob/4-2-stable/railties/CHANGELOG.md) for previous changes.