RubyMine 2018.3.2 (build 183.4886.48) has just been released. This new update brings support for Ruby 2.6 and its newly added endless ranges:
The new version also fixes a number of code insight and other issues.
See What’s new in RubyMine 2018.3 for the major improvements made in v2018.3.
Your RubyMine Team