Breaking change with `Yaml.safe_load`

[poloka]

Issue

It looks like psych-4.x included a breaking change to how YAML.safe_load executes causing a wrong number of arguments error when using the old format for performing a safe_load. Take specific note of the differences in the following output on the testing of Testing 'YAML.safe_load' with options: ([], [], true) using psych-3.3.2 on 2.6.6 vs Testing 'YAML.safe_load' with options: ([], [], true) using psych-4.0.3 on 2.6.6.

Investigation

Using the following code:

require 'yaml'
require 'erb'

def file_path
  file_path = File.join(Dir.pwd, 'test.yml')
end

def safe_load_old(**options)
  puts '*' * 100
  puts "Testing 'YAML.safe_load' with options: ([], [], #{options[:aliases]}) using psych-#{Psych::VERSION} on #{RUBY_VERSION}"
  call_function do
    puts YAML.safe_load(ERB.new(File.read(file_path)).result, [], [], options[:aliases])
  end
end

def safe_load_new(**options)
  puts '*' * 100
  puts "Testing 'YAML.safe_load' with options: (#{options}) using psych-#{Psych::VERSION} on #{RUBY_VERSION}"
  call_function do
    puts YAML.safe_load(ERB.new(File.read(file_path)).result, **options)
  end
end

def call_function
  yield
rescue Psych::DisallowedClass, Psych::BadAlias, Errno::ENOENT, ArgumentError => e
  puts "Error loading the '#{file_path}' located at '#{file_path}'. #{e.message}"
  puts "Backtrace:\n\t#{e.backtrace.join("\n\t")}"
end

safe_load_old(aliases: false)
safe_load_old(aliases: true)
safe_load_new(aliases: false)
safe_load_new(aliases: true)

Loading the following file:

default: &default
 enabled: true
 output: <%= ENV['TIMBER_OUTPUT'] || 'STDOUT' %>
 format: <%= ENV['TIMBER_FORMAT'] || 'JSON' %>

development:
 <<: *default

staging:
 <<: *default

Ruby 2.6 with psych-3.3.2 output

****************************************************************************************************
Testing 'YAML.safe_load' with options: ([], [], false) using psych-3.3.2 on 2.6.6
Error loading the '/Users/gh7199/temp/psych_tests/test.yml' located at '/Users/gh7199/temp/psych_tests/test.yml'. Unknown alias: default
Backtrace:
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:430:in `visit_Psych_Nodes_Alias'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:345:in `block in revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `each'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `each_slice'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:167:in `visit_Psych_Nodes_Mapping'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:345:in `block in revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `each'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `each_slice'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:167:in `visit_Psych_Nodes_Mapping'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:318:in `visit_Psych_Nodes_Document'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych.rb:362:in `safe_load'
        /Users/gh7199/temp/psych_tests/safe_load.rb:12:in `block in safe_load_old'
        /Users/gh7199/temp/psych_tests/safe_load.rb:25:in `call_function'
        /Users/gh7199/temp/psych_tests/safe_load.rb:11:in `safe_load_old'
        /Users/gh7199/temp/psych_tests/safe_load.rb:31:in `<top (required)>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:395:in `require'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:395:in `block in load_modules'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:393:in `each'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:393:in `load_modules'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:21:in `setup'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb.rb:412:in `start'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/exe/irb:11:in `<top (required)>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/irb:23:in `load'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/irb:23:in `<main>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/ruby_executable_hooks:22:in `eval'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/ruby_executable_hooks:22:in `<main>'
****************************************************************************************************
Testing 'YAML.safe_load' with options: ([], [], true) using psych-3.3.2 on 2.6.6
{"default"=>{"enabled"=>true, "output"=>"STDOUT", "format"=>"JSON"}, "development"=>{"enabled"=>true, "output"=>"STDOUT", "format"=>"JSON"}, "staging"=>{"enabled"=>true, "output"=>"STDOUT", "format"=>"JSON"}}
****************************************************************************************************
Testing 'YAML.safe_load' with options: ({:aliases=>false}) using psych-3.3.2 on 2.6.6
Error loading the '/Users/gh7199/temp/psych_tests/test.yml' located at '/Users/gh7199/temp/psych_tests/test.yml'. Unknown alias: default
Backtrace:
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:430:in `visit_Psych_Nodes_Alias'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:345:in `block in revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `each'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `each_slice'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:167:in `visit_Psych_Nodes_Mapping'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:345:in `block in revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `each'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `each_slice'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:343:in `revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:167:in `visit_Psych_Nodes_Mapping'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:318:in `visit_Psych_Nodes_Document'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-3.3.2/lib/psych.rb:362:in `safe_load'
        /Users/gh7199/temp/psych_tests/safe_load.rb:20:in `block in safe_load_new'
        /Users/gh7199/temp/psych_tests/safe_load.rb:25:in `call_function'
        /Users/gh7199/temp/psych_tests/safe_load.rb:19:in `safe_load_new'
        /Users/gh7199/temp/psych_tests/safe_load.rb:33:in `<top (required)>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:395:in `require'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:395:in `block in load_modules'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:393:in `each'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:393:in `load_modules'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:21:in `setup'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb.rb:412:in `start'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/exe/irb:11:in `<top (required)>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/irb:23:in `load'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/irb:23:in `<main>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/ruby_executable_hooks:22:in `eval'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/ruby_executable_hooks:22:in `<main>'
****************************************************************************************************
Testing 'YAML.safe_load' with options: ({:aliases=>true}) using psych-3.3.2 on 2.6.6
{"default"=>{"enabled"=>true, "output"=>"STDOUT", "format"=>"JSON"}, "development"=>{"enabled"=>true, "output"=>"STDOUT", "format"=>"JSON"}, "staging"=>{"enabled"=>true, "output"=>"STDOUT", "format"=>"JSON"}}

Ruby 2.6 with psych-4.0.3 output

****************************************************************************************************
Testing 'YAML.safe_load' with options: ([], [], false) using psych-4.0.3 on 2.6.6
Error loading the '/Users/gh7199/temp/psych_tests/test.yml' located at '/Users/gh7199/temp/psych_tests/test.yml'. wrong number of arguments (given 4, expected 1)
Backtrace:
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych.rb:323:in `safe_load'
        /Users/gh7199/temp/psych_tests/safe_load.rb:12:in `block in safe_load_old'
        /Users/gh7199/temp/psych_tests/safe_load.rb:25:in `call_function'
        /Users/gh7199/temp/psych_tests/safe_load.rb:11:in `safe_load_old'
        /Users/gh7199/temp/psych_tests/safe_load.rb:31:in `<top (required)>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:395:in `require'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:395:in `block in load_modules'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:393:in `each'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:393:in `load_modules'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:21:in `setup'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb.rb:412:in `start'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/exe/irb:11:in `<top (required)>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/irb:23:in `load'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/irb:23:in `<main>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/ruby_executable_hooks:22:in `eval'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/ruby_executable_hooks:22:in `<main>'
****************************************************************************************************
Testing 'YAML.safe_load' with options: ([], [], true) using psych-4.0.3 on 2.6.6
Error loading the '/Users/gh7199/temp/psych_tests/test.yml' located at '/Users/gh7199/temp/psych_tests/test.yml'. wrong number of arguments (given 4, expected 1)
Backtrace:
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych.rb:323:in `safe_load'
        /Users/gh7199/temp/psych_tests/safe_load.rb:12:in `block in safe_load_old'
        /Users/gh7199/temp/psych_tests/safe_load.rb:25:in `call_function'
        /Users/gh7199/temp/psych_tests/safe_load.rb:11:in `safe_load_old'
        /Users/gh7199/temp/psych_tests/safe_load.rb:32:in `<top (required)>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:395:in `require'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:395:in `block in load_modules'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:393:in `each'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:393:in `load_modules'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:21:in `setup'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb.rb:412:in `start'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/exe/irb:11:in `<top (required)>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/irb:23:in `load'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/irb:23:in `<main>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/ruby_executable_hooks:22:in `eval'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/ruby_executable_hooks:22:in `<main>'
****************************************************************************************************
Testing 'YAML.safe_load' with options: ({:aliases=>false}) using psych-4.0.3 on 2.6.6
Error loading the '/Users/gh7199/temp/psych_tests/test.yml' located at '/Users/gh7199/temp/psych_tests/test.yml'. Unknown alias: default
Backtrace:
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:430:in `visit_Psych_Nodes_Alias'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:345:in `block in revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:343:in `each'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:343:in `each_slice'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:343:in `revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:167:in `visit_Psych_Nodes_Mapping'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:345:in `block in revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:343:in `each'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:343:in `each_slice'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:343:in `revive_hash'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:167:in `visit_Psych_Nodes_Mapping'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:318:in `visit_Psych_Nodes_Document'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/visitor.rb:30:in `visit'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/visitor.rb:6:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych/visitors/to_ruby.rb:35:in `accept'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/psych-4.0.3/lib/psych.rb:335:in `safe_load'
        /Users/gh7199/temp/psych_tests/safe_load.rb:20:in `block in safe_load_new'
        /Users/gh7199/temp/psych_tests/safe_load.rb:25:in `call_function'
        /Users/gh7199/temp/psych_tests/safe_load.rb:19:in `safe_load_new'
        /Users/gh7199/temp/psych_tests/safe_load.rb:33:in `<top (required)>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:395:in `require'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:395:in `block in load_modules'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:393:in `each'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:393:in `load_modules'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb/init.rb:21:in `setup'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/lib/irb.rb:412:in `start'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/gems/irb-1.4.1/exe/irb:11:in `<top (required)>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/irb:23:in `load'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/irb:23:in `<main>'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/ruby_executable_hooks:22:in `eval'
        /Users/gh7199/.rvm/gems/ruby-2.6.6@psych_tests/bin/ruby_executable_hooks:22:in `<main>'
****************************************************************************************************
Testing 'YAML.safe_load' with options: ({:aliases=>true}) using psych-4.0.3 on 2.6.6
{"default"=>{"enabled"=>true, "output"=>"STDOUT", "format"=>"JSON"}, "development"=>{"enabled"=>true, "output"=>"STDOUT", "format"=>"JSON"}, "staging"=>{"enabled"=>true, "output"=>"STDOUT", "format"=>"JSON"}}

[ixti]

It's not only about safe_load it also breaks load and load_file as well when anchors are used:

# file: test.rb
require "yaml"

puts "RUBY:    #{RUBY_VERSION}"
puts "PSYCH:   #{Psych::VERSION}"
puts "LIBYAML: #{Psych::LIBYAML_VERSION}"

source = <<~YAML
  foo: &foo
    a: 1
    b: 2
  bar:
    <<: *foo
    a: 2
YAML

puts YAML.load(source)

---

$ chruby-exec ruby-3.0 -- ruby ./test.rb
RUBY:    3.0.3
PSYCH:   3.3.2
LIBYAML: 0.2.5
{"foo"=>{"a"=>1, "b"=>2}, "bar"=>{"a"=>2, "b"=>2}}

$ chruby-exec ruby-3.1 -- ruby ./test.rb
RUBY:    3.1.0
PSYCH:   4.0.3
LIBYAML: 0.2.5
/home/ixti/.rubies/ruby-3.1.0/lib/ruby/3.1.0/psych/visitors/to_ruby.rb:430:in `visit_Psych_Nodes_Alias': Unknown alias: foo (Psych::BadAlias)
	from /home/ixti/.rubies/ruby-3.1.0/lib/ruby/3.1.0/psych/visitors/visitor.rb:30:in `visit'
	from /home/ixti/.rubies/ruby-3.1.0/lib/ruby/3.1.0/psych/visitors/visitor.rb:6:in `accept'
	from /home/ixti/.rubies/ruby-3.1.0/lib/ruby/3.1.0/psych/visitors/to_ruby.rb:35:in `accept'
        ...

[colemannugent]

Ran into this issue when devise_ldap_authenticatable attempted to parse a LDAP YAML config file that is almost identical to @poloka's original example.

It looks like load internally calls safe_load with a few preset options:

psych/lib/psych.rb

Lines 369 to 376 in ba203f1

	def self.load yaml, permitted_classes: [Symbol], permitted_symbols: [], aliases: false, filename: nil, fallback: nil, symbolize_names: false, freeze: false
	safe_load yaml, permitted_classes: permitted_classes,
	permitted_symbols: permitted_symbols,
	aliases: aliases,
	filename: filename,
	fallback: fallback,
	symbolize_names: symbolize_names,
	freeze: freeze

Based on a quick glance, it looks like this commit 1764942 8 months ago by @tenderlove is when this behavior was introduced.

---

I'm currently working around this by removing the anchor and aliases and manually duplicating some config.

I'm still kinda new to the Ruby software ecosystem, but this seems particularly annoying since most users of Psych don't pull it in as a gem and thus don't explicitly vendor it in their Gemfiles.

[tenderlove]

@colemannugent if the YAML documents you're loading are trusted (IOW can't be controlled by external users) you can use YAML.unsafe_load

[colemannugent]

@tenderlove In this case I'm not calling Psych directly. I ran into this issue when a gem I use (devise_ldap_authenticatable) attempted to parse a YAML config file that I used anchors and aliases in to avoid repetition.

It looks like the way to resolve this is to alert most downstream users of Psych that they'll have examine where they load YAML and determine if it's safe to use unsafe_load.

[nbeyer]

FWIW - A contributor to this situation is an update to rdoc for version 6.4. Version 6.4 of rdoc added a psych >= 4.0.0 dependency. It seems rdoc is requiring a major version change to a dependency in a minor version change.

[dgm]

I also ran into this from a github dependabot upgrade of rdoc. (sdoc -> rdoc -> psych)