Notes from Rails 6.1 to 8.1 in a day

My invoicing app was on Rails 6.1 and Ruby 3.1. I meant to move it to Rails 7.0 and Ruby 3.4, and it went well enough that I kept going to 8.1 the same day. Production deploys with Capistrano, and development runs in Docker on Alpine. These are the four things that broke.

Uglifier couldn’t read the new JavaScript. On Rails 7.0, asset precompile failed:

Uglifier::Error: Unexpected token: keyword (const). To use ES6 syntax, harmony mode must be enabled with Uglifier.new(:harmony => true).

Rails 7.0’s Active Storage JavaScript uses const and class. Harmony mode got past that, but on Rails 7.1 precompile failed again with an empty Uglifier::Error. The 7.1 JavaScript uses ?., ??, and ||=, and Uglifier’s harmony mode can’t parse any of them. Terser can:

gem 'terser'
config.assets.js_compressor = :terser

That deployed cleanly, even with the old Node on the server. Skip harmony mode and go straight to terser.

The Docker image built but wouldn’t boot. rails db:prepare failed with an OpenSSL LoadError. The Dockerfile copies libssl and libcrypto from a wkhtmltopdf image into the Ruby image, so PDF generation works on Alpine. The Ruby image’s tag had moved to a newer Alpine release than the wkhtmltopdf image, so the copied libraries didn’t match the rest of the system. Pinning both to the same release fixed it:

FROM surnet/alpine-wkhtmltopdf:3.23.4-0.12.6-small AS wkhtmltopdf
FROM ruby:3.4.10-alpine3.23

If one stage copies shared libraries from another, pin both to the same release.

=~ on an Integer. Specs failed with undefined method '=~' for an instance of Integer. Ruby 3.2 removed Object#=~, so it only works on strings, regexps, and nil now. A setter got an Integer from parsed JSON and called =~ on it. A type check fixed it:

if string.is_a?(String) && string.include?(":")

The PDF template had a format in its name. In production, Download PDF returned 500 with ActionView::MissingTemplate. The controller rendered template: "invoices/download.pdf". Rails 6.1 removed the .pdf and found download.pdf.erb. Rails 7 keeps it and looks for download.pdf.pdf.erb. Removing the suffix fixed it, and production returned 200 with application/pdf. A request spec that downloads the PDF catches this kind of change before it ships.