Rails 5 Upgrade: routes.rb file cleared out

Question

I am upgrading a Rails app from 4.2.x to 5.0.x. After I updated all my Rails-related gems in Gemfile, I ran the rails task for updating all my files to conform to the newest version, as per the upgrade guide:

rails app:update

There were many conflicts in this command, so I pressed a to accept all conflicts and then review them manually before committing them. My main concern is what happened to the config/routes.rb file. Basically, the entire contents of the file, save for the Rails.application.routes.draw block and a single comment about the DSL added to the end of the file, were kept. All routes that have been added to the app over the years were cleared out, not to be found in any other file.

This issue doesn't block me, I'll simply checkout the file to bring it back to its former state. However, what especially concerns me is that an essential file was cleared out in what appears to be a normal situation for upgrading a Rails version. I'd like to see if anyone else has run into this issue, whether this is expected, what's going on. Comments from Rails maintainers are welcome. Thank you.

Answer 1

The app:update task is just a slightly modified version of the task that creates a new Rails application. It writes out files under config/ and bin/ based on the templates from the new Rails version. If you selected a to accept all conflicts, then that simply means that Rails is going to overwrite any differing files with its own copy without asking you. This is normal and expected. If you don't want that behavior, then don't press a.

config/routes.rb is almost certainly the one file under config/ that will differ almost completely from the empty boilerplate file. Realistically, Rails can't be expected to parse your custom changes and merge them with a new template.

For what it's worth, I like to start out doing exactly what you did, with a clean working directory just let the app:update task overwrite anything it wants to, and then go through all the changes with a side-by-side, SCM-aware diff tool like vim-fugitive to stage or discard the differences.