Why doesn't 'USER INSTALLATION DIRECTORY' match with the Ruby version?

Question

This question was the second part of " What is "USER INSTALLATION DIRECTORY" in rubyGems env " but finally it wasn't answered.

Now I'm wondering why in my case 'USER INSTALLATION DIRECTORY does not mach with the Ruby version. And another question is what option bundle install uses by default, maybe --user-install ?

rvm list :

 * ruby-2.5.0 [ x86_64 ]
=> ruby-2.5.1 [ x86_64 ]
   ruby-2.6.0-preview1 [ x86_64 ]

gem env :

RubyGems Environment:
  - RUBYGEMS VERSION: 2.7.7
  - RUBY VERSION: 2.5.1 (2018-03-29 patchlevel 57) [x86_64-linux]
  - INSTALLATION DIRECTORY: /home/ivan/.rvm/gems/ruby-2.5.1
  - USER INSTALLATION DIRECTORY: /home/ivan/.gem/ruby/2.5.0
  ...

Answer 1

The installation directory for Gems is based on the library compatibility version of Ruby. Since Ruby 2.5.1 is library-compatible with Ruby 2.5.0, its library compatibility version is still 2.5.0.