Gemsets seem to cause problems in the new Trusty image

[bellkev]

E.g. https://circleci.com/gh/bellkev/gemset-bundler-issue/5 failed where it worked on Precise.

[eric-hu]

This could be one of two problems:

1. RVM changed its behavior in newer versions. It previously ran gem install bundler whenever it installed a new Ruby version, but no longer does.

The fix for this is to add gem install bundler to the Ruby install code.

1. Bundler has an issue with doubly-nested bundle exec. bundle exec cmd is used to launch a Ruby command using only the gems installed by Bundler, specified by a Gemfile.

Running bundle exec bundle exec bundle exec ... bundle exec ls should be equivalent to bundle exec ls, but the former errors out. No one actually runs commands that way, but a Ruby gem executable might shell out to other Ruby gem executables, and the effect is equivalent to bundle exec bundle exec second_cmd.

This issue is on-and-off, as in: it's marked solved by the bundler team and then re-opened. I think in the latest version it's still somewhat present. I've suggested a fix for customers is to use an older version of Bundler...I think 2.4.8.

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To determine if it's 1 or 2, running bundle exec ls will error out if it's the 1nd case. If it's the 2nd case, the output will be the same as ls and bundle exec bundle exec ls will error out.