Revert "* lib/yaml.rb: Remove Psych::EngineManager [Bug #8344]"

zzak is not the maintainer of yaml.
This reverts commit r46097.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46102 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 34 insertions, 0 deletions

diff --git a/lib/yaml.rb b/lib/yaml.rb
index c0ffcf877b..3b4e4234f7 100644
--- a/lib/yaml.rb
+++ b/lib/yaml.rb
@@ -12,6 +12,40 @@ end
 
 YAML = Psych # :nodoc:
 
+module Psych # :nodoc:
+  # For compatibility, deprecated
+  class EngineManager # :nodoc:
+    attr_reader :yamler # :nodoc:
+
+    def initialize # :nodoc:
+      @yamler = 'psych'
+    end
+
+    def syck? # :nodoc:
+      false
+    end
+
+    # Psych is always used and this method has no effect.
+    #
+    # This method is still present for compatibility.
+    #
+    # You may still use the Syck engine by installing
+    # the 'syck' gem and using the Syck constant.
+    def yamler= engine # :nodoc:
+      case engine
+      when 'syck' then warn "syck has been removed, psych is used instead"
+      when 'psych' then @yamler = 'psych'
+      else
+        raise(ArgumentError, "bad engine")
+      end
+
+      engine
+    end
+  end
+
+  ENGINE = EngineManager.new # :nodoc:
+end
+
 # YAML Ain't Markup Language
 #
 # This module provides a Ruby interface for data serialization in YAML format.