(PUP-11405) Replace deprecated/changed Psych YAML methods, pin rdoc

The keyword variant of safe_load() was added and the old variant deprecated in
Psych 3.1.0. It has been removed in 4.0.0 (ruby/psych@0767227).

The load_file() method was changed to be safe in Psych 4.0.1 (ruby/psych@f8a5e51).
Use the unsafe_load_file() introduced in 3.3.2 to keep the same behaviour.

The usages are guarded by version checks since Puppet still supports Ruby 2.5,
which ships Psych 3.0.2.

Also pin rdoc to prevent 6.0.4, which depends on Psych 4.0 causing issues with
other dependencies that haven't been updated yet to work due to the same
changes.

Author: tambry

Gemfile

@@ -29,7 +29,7 @@ group(:features) do
   #gem 'ruby-shadow', '~> 2.5', require: false, platforms: [:ruby]
   gem 'minitar', '~> 0.9', require: false
   gem 'msgpack', '~> 1.2', require: false
-  gem 'rdoc', '~> 6.0', require: false, platforms: [:ruby]
+  gem 'rdoc', ['~> 6.0', '< 6.4.0'], require: false, platforms: [:ruby]
   # requires native augeas headers/libs
   # gem 'ruby-augeas', require: false, platforms: [:ruby]
   # requires native ldap headers/libs

lib/puppet/util/yaml.rb

@@ -24,7 +24,11 @@ class YamlLoadError < Puppet::Error; end
   # @raise [YamlLoadException] If deserialization fails.
   # @return The parsed YAML, which can be Hash, Array or scalar types.
   def self.safe_load(yaml, allowed_classes = [], filename = nil)
-    data = YAML.safe_load(yaml, allowed_classes, [], true, filename)
+    if Gem::Version.new(Psych::VERSION) >= Gem::Version.new('3.1.0')
+      data = YAML.safe_load(yaml, permitted_classes: allowed_classes, aliases: true, filename: filename)
+    else
+      data = YAML.safe_load(yaml, allowed_classes, [], true, filename)
+    end
     data = false if data.nil?
     data
   rescue ::Psych::DisallowedClass => detail
@@ -68,7 +72,11 @@ def self.load_file(filename, default_value = false, strip_classes = false)
       end
       data.to_ruby || default_value
     else
-      yaml = YAML.load_file(filename)
+      if Gem::Version.new(Psych::VERSION) >= Gem::Version.new('3.3.2')
+        yaml = YAML.unsafe_load_file(filename)
+      else
+        yaml = YAML.load_file(filename)
+      end
       yaml || default_value
     end
   rescue *YamlLoadExceptions => detail