Support jsbundling-rails (Rails 7): Yarn appears to only be available alongside Webpacker

[dwightwatson]

I'm experimenting with a Rails 7.x alpha app on Heroku, which now provides an alternative to Webpacker call jsbundling-rails. These bundlers effectively run externally of Rails and inject their builds into the regular old asset pipeline.

They still expect yarn to be available to install and build, but it appears as though yarn may not be available if Webpacker isn't detected.

-----> Preparing app for Rails asset pipeline
       Running: rake assets:precompile
       sh: 1: yarn: not found
       sh: 1: yarn: not found
       Asset precompilation completed (1.52s)
       Cleaning assets
       Running: rake assets:clean

The easy solution is to add the heroku/nodejs buildpack and then it'll build fine. But if the ruby buildpack already includes support for yarn perhaps it should always be available, or better at detecting when it's required. Perhaps the presence of a package.json or yarn.lock should be a good enough hint to make it available?

[schneems]

Thanks for the report. In the past we've gated based on the presence of certain gems, currently, we gate on webpacker and execjs.

Perhaps the presence of a package.json or yarn.lock should be a good enough hint to make it available

That seems much less piecemeal. I've added a card to work on this. We're in the middle of a deploy freeze due to dreamforce but that's over at the end of the week.