1 files changed, 64 insertions, 69 deletions
diff --git a/lib/yaml.rb b/lib/yaml.rb
index ff9e1a6344..c6f0f89fd2 100644
--- a/lib/yaml.rb
+++ b/lib/yaml.rb
@@ -1,76 +1,71 @@
-##
-# The YAML module allows you to use one of the two YAML engines that ship with
-# ruby.  By default Psych is used but the old and unmaintained Syck may be
-# chosen.
+# frozen_string_literal: false
+
+begin
+  require 'psych'
+rescue LoadError
+  case RUBY_ENGINE
+  when 'jruby'
+    warn "The Psych YAML extension failed to load.\n" \
+      "Check your env for conflicting versions of SnakeYAML\n" \
+      "See https://github.com/jruby/jruby/wiki/FAQs#why-does-the-psych-yaml-extension-fail-to-load-in-my-environment",
+         uplevel: 1
+  else
+    warn "It seems your ruby installation is missing psych (for YAML output).\n" \
+      "To eliminate this warning, please install libyaml and reinstall your ruby.\n",
+         uplevel: 1
+  end
+  raise
+end
+
+YAML = Psych # :nodoc:
+
+# YAML Ain't Markup Language
 #
-# See Psych or Syck for usage and documentation.
+# This module provides a Ruby interface for data serialization in YAML format.
 #
-# To set the YAML engine to syck:
+# The YAML module is an alias of Psych, the YAML engine for Ruby.
 #
-#   YAML::ENGINE.yamler = 'syck'
+# == Usage
 #
-# To set the YAML engine back to psych:
+# Working with YAML can be very simple, for example:
 #
-#   YAML::ENGINE.yamler = 'psych'
-
+#     require 'yaml'
+#     # Parse a YAML string
+#     YAML.load("--- foo") #=> "foo"
+#
+#     # Emit some YAML
+#     YAML.dump("foo")     # => "--- foo\n...\n"
+#     { :a => 'b'}.to_yaml  # => "---\n:a: b\n"
+#
+# As the implementation is provided by the Psych library, detailed documentation
+# can be found in that library's docs (also part of standard library).
+#
+# == Security
+#
+# Do not use YAML to load untrusted data. Doing so is unsafe and could allow
+# malicious input to execute arbitrary code inside your application. Please see
+# doc/security.rdoc for more information.
+#
+# == History
+#
+# Syck was the original YAML implementation in Ruby's standard library
+# developed by why the lucky stiff.
+#
+# You can still use Syck, if you prefer, for parsing and emitting YAML, but you
+# must install the 'syck' gem now in order to use it.
+#
+# In older Ruby versions, ie. <= 1.9, Syck is still provided, however it was
+# completely removed with the release of Ruby 2.0.0.
+#
+# == More info
+#
+# For more advanced details on the implementation see Psych, and also check out
+# http://yaml.org for spec details and other helpful information.
+#
+# Psych is maintained by Aaron Patterson on github: https://github.com/ruby/psych
+#
+# Syck can also be found on github: https://github.com/ruby/syck
 module YAML
-  class EngineManager # :nodoc:
-    attr_reader :yamler
-
-    def initialize
-      @yamler = nil
-    end
-
-    def syck?
-      'syck' == @yamler
-    end
-
-    def yamler= engine
-      raise(ArgumentError, "bad engine") unless %w{syck psych}.include?(engine)
-
-      require engine unless (engine == 'syck' ? Syck : Psych).const_defined?(:VERSION)
-
-      Object.class_eval <<-eorb, __FILE__, __LINE__ + 1
-        remove_const 'YAML'
-        YAML = #{engine.capitalize}
-        remove_method :to_yaml
-        alias :to_yaml :#{engine}_to_yaml
-      eorb
-
-      @yamler = engine
-      engine
-    end
-  end
-
-  ##
-  # Allows changing the current YAML engine.  See YAML for details.
-
-  ENGINE = YAML::EngineManager.new
+  # The version of YAML wrapper
+  LOADER_VERSION = "0.4.0"
 end
-
-if defined?(Psych)
-  engine = 'psych'
-elsif defined?(Syck)
-  engine = 'syck'
-else
-  begin
-    require 'psych'
-    engine = 'psych'
-  rescue LoadError
-    warn "#{caller[0]}:"
-    warn "It seems your ruby installation is missing psych (for YAML output)."
-    warn "To eliminate this warning, please install libyaml and reinstall your ruby."
-    require 'syck'
-    engine = 'syck'
-  end
-end
-
-module Syck
-  ENGINE = YAML::ENGINE
-end
-
-module Psych
-  ENGINE = YAML::ENGINE
-end
-
-YAML::ENGINE.yamler = engine