"Yarn is good. Yarn works."

Last week, we mentioned that Rails 5.1 is gaining a --yarn option. This option is now promoted to be the default: every new Rails app will be set up to use yarn out-of-the-box. It's also worth noting that yarn packages are now installed into the vendor/node_modules directory.

Basic webpack integration

While we are talking about JavaScript, the asset bundling side of things is also getting some love. Rails 5.1 will gain first-class support for webpack via the --webpack option. This is still a pretty early spike, so definitely try it out and help improve it.

Change default primary keys to BIGINTs

Friends don't let friends use INT as a primary key – your app might hit Webscale™ before you know it, resulting in much sadness when your primary key column overflows. To help put you on the right path, Rails 5.1 will default to using BIGINTs for primary key columns in MySQL and PostgreSQL.

Introduce `ActiveRecord::NotNullViolation` error

As of this pull request, if your model failed to save due to a NOT NULL constraint, Rails will raise a NotNullViolation error (instead of a generic StatementInvalid error) so you could rescue the error and handle it appropriately.

Speeding up RSpec integration tests by 40%

This patch fixes an issue where templates are needlessly recompiled between integration test, resulting in a significant speedup.

Idempotent `after_commit` callbacks

Previously, certain race conditions could cause your after_commit callbacks to fire more often than expected. This patch attempts to more accurately track the work that actually happened in the database to ensure your hooks are triggered only when appropriate.

Allow variales named `block` in templates

Have you tried using variables named block in your templates? If you did, you might have seen a pretty strange error from Rails. Not anymore! With this patch, you would be able to do that without issues.

Exclude singleton classes from `subclasses` and `descendants`

A change in Ruby 2.3.0 unexpectedly changed the behavior of Active Support's Class#subclasses and Class#descendants methods to include singleton classes. This patch restores the previous behavior and made things consistent across different versions of Ruby (again).