A few notes on upgrading to Rails 6

I had the opportunity to upgrade 3 Rails apps. Here are some notes from that experience.

Upgrade guide

gem "rails", "~> 6.0.0"

# bootsnap needs to be >= 1.4.2
gem "bootsnap", ">= 1.4.2", require: false

bundle update rails

- config.load_defaults 5.2
+ config.load_defaults 6.0

This is the minimum, quite straightforward.

I prefer to also run bin/rails app:update to get the latest configs. Although many of them can be just fixing punctuations or removing unneeded configurations, I prefer to keep config closer to what I'll get when I run a fresh rails new app. 🙂

A few notes on rails app:update

After running rails app:update and reviewing the changes, most looked good. I only searched a few that stand out.

- config.action_controller.perform_caching = true

One of the apps I upgraded is running on config.api_mode = true, with that config, the app:update command will generate this change.

This is because the config is irrelavent for api_mode app, "because we don't provide view caching and doesn't include ActionController::Caching for api apps." Removing this config is to avoid confusing people.

Note that it won't change the existing behavior.

Learn more: https://github.com/rails/rails/pull/36067

Next, we got this config.cache_classes to changed to false for test.

- config.cache_classes = true
+ config.cache_classes = false

This responsibility seems to be delegated to Spring now based on this commit.

Sprockets: Lock to major version 3

When I run bundle update rails, for two apps that have been running on Sprockets V3 got bumped to V4. That was a major upgrade, which requires you take actions. (See the upgrade guide.)

I tried to upgrade but had encountered some errors and my css won't compile. I decided to not invest anymore and reverted it back to V3 by adding this line to my Gemfile:

gem 'sprockets', '~> 3.0'

The reason being: V3 still works, and I plan to migrate all the assets to Webpack soon anyway.

You can check my previous post on Active Storage with Rails 6.

http://railsdiff.org/5.2.0/6.0.0 can also be handy.