Bundler 2.0.1 installed, Rails says “must use Bund

Question

I'm a Rails newb who's trying out Rails on a DigitalOcean droplet. The installations seemed to work fine, but I'm getting a curious error message when I try to generate a scaffold:

DO 10:48 Rails/simple (master) → rails generate scaffold User name:string email:string
Traceback (most recent call last):
        5: from bin/rails:3:in `<main>'
        4: from bin/rails:3:in `load'
        3: from /home/tony/rails/simple/bin/spring:10:in `<top (required)>'
        2: from /home/tony/rails/simple/bin/spring:10:in `new'
        1: from /home/tony/.rvm/rubies/ruby-2.6.0/lib/ruby/2.6.0/bundler/lockfile_parser.rb:95:in `initialize'
/home/tony/.rvm/rubies/ruby-2.6.0/lib/ruby/2.6.0/bundler/lockfile_parser.rb:108:in `warn_for_outdated_bundler_version': You must use Bundler 2 or greater with this lockfile. (Bundler::LockfileError)
DO 10:49 Rails/simple (master) → bundle list bundler
/home/tony/.rvm/gems/ruby-2.6.0/gems/bundler-2.0.1
DO 10:50 Rails/simple (master) → gem list bundler

*** LOCAL GEMS ***

bundler (2.0.1, default: 1.17.2)
bundler-unload (1.0.2)
rubygems-bundler (1.4.5)

I.e., the current Bundler gem is version 2.0.1, but Rails still thinks it's insufficient.

I can't find anything similar on the web. The only red flag I can see is that the bundler gem shows a default version of 1.17.2. How do I begin to diagnose the problem?

Answer 1

Just had this issue as well trying to push to my Heroku project. Found the answer in another question and it worked for me: You must use Bundler 2 or greater with this lockfile

run: heroku buildpacks:set https://github.com/bundler/heroku-buildpack-bundler2

Then try generating again.

Answer 2

I ran into the same issue & resolved it by downgrading with gem uninstall bundler, followed by gem install bundler -v 1.17.3 to revert back to the last pre 2 version.

I saw this across 3 separate systems using different version managers (ASDF, rbenv, rvm) which led me to believe the 2.x release of bundler wasn't ready for production use yet.

There is some information on getting both versions to play nicely here but I haven't been successful with this either.