Ruby version 2.6.1 produces Unknown Ruby version error

My .rubocop.yml file defines a TargetRubyVersion of 2.6, the current version of Ruby set forth in my Gemfile.

On linting, this produces the error:

Error: Unknown Ruby version 2.6 found in `TargetRubyVersion` parameter (in /path/to/my/.rubocop.yml). Known versions: 1.9, 2.0, 2.1, 2.2, 2.3, 2.4

[benedictfritz]

The issue was that the version of rubocop was too old. We upgraded and the issue went away.

This inspired me to double-check my versioning, and I think something weird happened to me versioning-wise as well that caused this. I think I was unsure whether the vscode plugin was using system rubocop, the rubocop specified by the specific version of ruby I was running via rbenv, and the version of rubocop listed in the bundle.

In the end I got it fixed!

I un-confused myself by specifically telling the vscode plugin to use the Bundler version, and then making sure that Bundler has a more recent version of Rubocop installed that supports Ruby 2.6.

I did the following steps:

• Go to the vscode settings for the ruby-rubocop plugin (click the little gear on the plugins list)
• Check the box Ruby > Rubocop: Use Bundler to be explicit that I want to use the version listed in the Gemfile
• Ran bundle exec rubocop --version in the project directory, which ended up showing a different version from what I was expecting
• Set an explicit version number in the Gemfile i.e. gem 'rubocop', '~> 0.8'
• Ran bundle update rubocop in the project directory
• Ran bundle exec rubocop --version to confirm that the version I expected got installed

Hopefully this helps someone!

[jacobbeasley]

One note is if you updated rubocop, you may also have to update your config file. Sometimes old features get removed/deprecated/renamed.

Anyways, glad we tracked it down! Hopefully this post helps others.