Upgrade Sprockets 3 to 4 in a Rails project

There's a update guide at https://github.com/rails/sprockets/blob/master/UPGRADING.md Show archive.org snapshot

In short, must replace Rails.application.config.assets.precompile entries with link statements in Sprockets' manifest.js file.

Example: app/assets/stylesheets/frontend/all.sass and app/assets/stylesheets/backend/all.sass should be precompiled.

Sprockets 3:

CopyRails.application.config.assets.precompile += %w[
  backend/all.css
  frontend/all.css
]

Sprockets 4 manifest.js:

Copy//= link_tree ../images
//= link backend/all.css
//= link frontend/all.css

If you get couldn't find file 'base.sass' with type 'text/css' errors, replace something like

Copy*= require base.sass

with:

Copy*= require base

in your sass files.