This is a tracking ticket for increasing the minimum required Ruby version across our projects.

Currently all maintained versions of bson-ruby, driver and Mongoid require Ruby 2.3.

Requiring a minimum of Ruby 2.4 would allow us to use the following Ruby features:

Hash#compact
Integer unification (Fixnum gone, mostly affects docstrings)
Precision argument to rounding/truncation methods on floats (we are working around lack of this in 2.3 in bson-ruby)
String capacity reservation (we are working around lack of this in 2.3 in driver socket code)
Remove toolchain hacks to build Ruby 2.3 since it requires openssl 1.0
Speed up evergreen builds if we remove 2.3 from toolchain

Ruby branch maintenance status: https://www.ruby-lang.org/en/downloads/branches/

Presently 2.3 and 2.4 branches are EOL.

Ruby versions by OS:

Debian 10 (buster): 2.5
Debian 9 (stretch): 2.3
Ubuntu 18.04: 2.5
Ubuntu 16.04: 2.3
Ubuntu 14.04: ?
Centos 8: 2.5/2.6
Centos 7: 2.0