Which Ruby does Vim use for :ruby commands? - ruby

Question

Vim has support for Ruby commands. (For more information, please see the :help if-ruby documentation.) These commands can be run using :ruby if +ruby support is enabled (see vim --version). As an example, I can see that I'm currently using v3.0.0 by using:
:ruby print RUBY_VERSION
However, which Ruby installation is this? For example, is it system Ruby, something managed by RVM, or a ​separate Ruby installation that is built into Vim?
Also, is it possible to install Ruby gems to use with :ruby commands?
Details about my installation:
$ sw_vers
ProductName: Mac OS X
ProductVersion: 10.15.7
BuildVersion: 19H524
$ vim --version
VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Mar 21 2021 06:59:54)
macOS version - x86_64
Included patches: 1-2625
Compiled by Homebrew
[...]
$ vim --version | grep ruby
+cursorshape +lua +ruby +wildmenu
Linking: clang -L. -fstack-protector-strong -L/usr/local/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/openssl#1.1/lib -L/usr/local/opt/readline/lib -L/usr/local/lib -o vim -lncurses -liconv -lintl -framework AppKit -L/usr/local/opt/lua/lib -llua5.4 -mmacosx-version-min=10.15 -fstack-protector-strong -L/usr/local/lib -L/usr/local/Cellar/perl/5.32.1_1/lib/perl5/5.32.1/darwin-thread-multi-2level/CORE -lperl -lm -lutil -lc -L/usr/local/opt/python#3.9/Frameworks/Python.framework/Versions/3.9/lib/python3.9/config-3.9-darwin -lpython3.9 -framework CoreFoundation -lruby.3.0 -L/usr/local/Cellar/ruby/3.0.0_1/lib
$ which -a ruby
/Users/username/.rbenv/shims/ruby
/usr/bin/ruby
$ rbenv versions
system
* 2.6.5 (set by /Users/username/.rbenv/version)

Answer 1

All this depends on Vim build configuration. :ver output may indicate the following:
-lang interface for "lang" wasn't compiled at all;
+lang everything was statically linked into Vim executable;
+lang/dyn interface was linked against dynamic library (dll/so)
If it's linked dynamically then the library will be searched and loaded on demand by option value (e.g. :h 'rubydll'). In this case it may point to any installation you want. (Although -DRUBY_VERSION=XX specified at compile-time may still be relevant and Vim may fail to load mismatched library).

Answer 2

You don't mention your platform, or how you installed Vim. If we're talking about default behavior, these things matter.
Unless you statically compiled Ruby into Vim, it will be whichever Ruby is first in your PATH, or first in fish_user_paths if you use the fish shell. On macOS and typical desktop Linux distributions like Ubuntu, that's what you should expect out of the box.
Other ways to check include:
Using which -a ruby will show you all the rubies in your PATH.
If Ruby 3.0.0 is not the first item listed, or not the version installed to /usr/bin/ruby, then you can be pretty sure that something else is managing it.
Check env | fgrep -i ruby for settings from various Ruby managers.
Version managers usually work by modifying your environment. For example, chruby adds CHRUBY_VERSION to the environment, and RUBY_ROOT to set the path for the selected Ruby. Other common version managers will also update the environment in various ways, so this is a good place to look.
Check your shell initialization files (e.g. ~/.bashrc).
If you aren't setting up RVM, rbenv, or chruby in your shell's initialization script, then you probably aren't using one of them. Of course, that doesn't preclude the use of symlinks, GNU stow, or other redirections, but if you didn't set them up and aren't working on a multiuser system where someone else may have, then you can be pretty confident that invoking ruby is calling the Ruby that's first in your PATH.