So that pesky “allow placement of cursor after end of line” which manifests itself as seemingly infinite whitespace at the end of every line seems to be true of all Jetbrains IDEs. I’ve just found that RubyMine does the same thing as IntelliJ Idea.

You can turn it off in exactly the same way as you do in IntelliJ

• Go to the menu “RubyMine -> Preferences” (on OSX) or “Edit -> preferences” on windows.
  
• Then either just start typing “caret” in the seach box - or click on “editor” in the menu on the left.
  
• Then uncheck “Allow placement of caret after end of line” Just like in IntelliJ