Add extlib::compare_ip() function

This function is to be used with the built-in `sort()` function.

lib/puppet/functions/extlib/compare_ip.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require 'ipaddr'
+
+# A function that compares two IP addresses. To be used with the built-in sort()
+# function.
+Puppet::Functions.create_function(:'extlib::compare_ip') do
+  # @param a First value
+  # @param b Second value
+  # @return -1, 0 or 1 if first value is lesser, equal or greater than second value
+  # @example Sorting the array of IP addresses
+  #   $ip_addresses = ['10.1.1.1', '10.10.1.1', '10.2.1.1']
+  #   $ip_addresses.sort |$a, $b| { extlib::compare_ip($a, $b) }
+  dispatch :compare_ip do
+    param 'String[1]', :left
+    param 'String[1]', :right
+    return_type 'Integer[-1,1]'
+  end
+
+  def compare_ip(left, right)
+    IPAddr.new(left).to_i <=> IPAddr.new(right).to_i
+  end
+end

spec/functions/extlib/compare_ip_spec.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'extlib::compare_ip' do
+  it 'exists' do
+    is_expected.not_to be_nil
+  end
+
+  it { is_expected.to run.with_params('10.1.1.1', '10.2.1.1').and_return(-1) }
+  it { is_expected.to run.with_params('10.2.1.1', '10.2.1.1').and_return(0) }
+  it { is_expected.to run.with_params('10.10.1.1', '10.2.1.1').and_return(1) }
+
+  it { is_expected.to run.with_params('fe80::1', 'fe80::2').and_return(-1) }
+  it { is_expected.to run.with_params('fe80::2', 'fe80::2').and_return(0) }
+  it { is_expected.to run.with_params('fe80::10', 'fe80::2').and_return(1) }
+
+  it { is_expected.to run.with_params('0::ffff:fffe', '255.255.255.255').and_return(-1) }
+  it { is_expected.to run.with_params('0::ffff:ffff', '255.255.255.255').and_return(0) }
+  it { is_expected.to run.with_params('0::1:0:0', '255.255.255.255').and_return(1) }
+end