Drop Ruby 2.5 support

[mhashizume]

This PR:

• Raises Facter's minimum Ruby version from 2.5 to 2.6 in the gemspec.
• Updates unit tests to use Ruby 2.6 as their minimum version.
• Update Rubocop and related gems to the last version to support Ruby 2.6 and sets Ruby 2.6 as the TargetRubyVersion in rubocop.yml.
• Addresses new Rubocop offenses from the above updates.

[ekohl]

I think this broke puppetserver 7:

  Mar 06 15:43:30 centos7-64-puppet7.example.com puppetserver[4297]: SyntaxError: /opt/puppetlabs/puppet/lib/ruby/vendor_ruby/facter/util/api_debugger.rb:37: syntax error, unexpected '{ arg'
  Mar 06 15:43:30 centos7-64-puppet7.example.com puppetserver[4297]: exclude << option[1..].to_sym
  Mar 06 15:43:30 centos7-64-puppet7.example.com puppetserver[4297]: ^

I also see it in our Ubuntu 20.04 test in the same place. https://github.com/theforeman/puppet-puppet/actions/runs/8174732159/job/22350223689?pr=908

[joshcooper]

@ekohl are you running puppetserver in a container? I don't see this issue using puppetserver 7 packages on Ubuntu 20.04. As can be seen below, puppetserver's jruby maintains compatibility with Ruby 2.6.8, which supports [1..] syntax

# dpkg -l puppetserver
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version       Architecture Description
+++-==============-=============-============-=================================
ii  puppetserver   7.16.0-1focal all          Puppet Labs puppetserver

# /opt/puppetlabs/server/bin/puppetserver gem install --no-document facter
Fetching thor-1.3.1.gem
Fetching facter-4.6.1.gem
Successfully installed thor-1.3.1
Successfully installed facter-4.6.1
2 gems installed
# /opt/puppetlabs/server/bin/puppetserver irb
irb(main):001:0> require 'facter'
=> true
irb(main):002:0> Facter.to_hash.count
=> 116
irb(main):003:0> arr = [1, 2, 3]
=> [1, 2, 3]
irb(main):004:0> arr[1..]
=> [2, 3]
...
irb(main):007:0> option = '-one'
=> "-one"
irb(main):008:0> option[1..]
=> "one"
irb(main):009:0> option[1..].to_sym
=> :one
irb(main):010:0> RUBY_VERSION
=> "2.6.8"
irb(main):011:0> Facter::VERSION
=> "4.6.1"
irb(main):012:0> JRUBY_VERSION
=> "9.3.9.0"

[ekohl]

It is indeed a container, because it makes CI in GitHub Actions easier

[joshcooper]

You're installing latest puppet-agent:

  Setting up puppet-agent (7.29.1-1focal) ...

But installing a two+ year old puppetserver 7.6.0. That version vendors an older JRuby 9.2, hence the error:

root@diffuse-produce:~# dpkg -s puppetserver
Package: puppetserver
Status: install ok installed
Priority: optional
Section: utils
Installed-Size: 102908
Maintainer: Puppet Labs <info@puppetlabs.com>
Architecture: all
Version: 7.6.0-1focal
...
root@diffuse-produce:~# /opt/puppetlabs/server/bin/puppetserver --version
puppetserver version: 7.6.0
root@diffuse-produce:~# /opt/puppetlabs/server/bin/puppetserver irb
irb(main):001:0> RUBY_VERSION
=> "2.5.8"
irb(main):002:0> JRUBY_VERSION
=> "9.2.17.0"
irb(main):003:0> "one"[1..]
Traceback (most recent call last):
        7: from -e:1:in `<main>'
        6: from org/jruby/RubyKernel.java:1009:in `load'
        5: from /opt/puppetlabs/server/apps/puppetserver/puppet-server-release.jar!/META-INF/jruby.home/bin/irb:17:in `<main>'
        4: from org/jruby/RubyKernel.java:1189:in `catch'
        3: from org/jruby/RubyKernel.java:1189:in `catch'
        2: from org/jruby/RubyKernel.java:1442:in `loop'
        1: from org/jruby/RubyKernel.java:1048:in `eval'
SyntaxError ((irb):4: syntax error, unexpected '{ arg')
"one"[1..]

While we always aim to maintain compatibility within 7.x, the combination of latest agent and ancient puppetserver on the same host seems like a recipe for disaster.

[ekohl]

Hmm, interesting. We historically had that test to verify upgrades. Maybe we should raise the base version a bit