From f9764c806980a663dbc75a8ec1764d02a225595d Mon Sep 17 00:00:00 2001
From: Aaron Patterson <aaron.patterson@gmail.com>
Date: Tue, 29 Sep 2009 17:16:29 -0700
Subject: aliases can be emitted

---
 ext/psych/emitter.c           | 17 +++++++++++++++++
 lib/psych/visitors/emitter.rb |  4 ++++
 test/visitors/test_emitter.rb | 15 +++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/ext/psych/emitter.c b/ext/psych/emitter.c
index d6b13f9..126f174 100644
--- a/ext/psych/emitter.c
+++ b/ext/psych/emitter.c
@@ -210,6 +210,22 @@ static VALUE end_mapping(VALUE self)
   return self;
 }
 
+static VALUE alias(VALUE self, VALUE anchor)
+{
+  yaml_emitter_t * emitter;
+  Data_Get_Struct(self, yaml_emitter_t, emitter);
+
+  yaml_event_t event;
+  yaml_alias_event_initialize(
+      &event,
+      (yaml_char_t *)(Qnil == anchor ? NULL : StringValuePtr(anchor))
+  );
+
+  emit(emitter, &event);
+
+  return self;
+}
+
 void Init_psych_emitter()
 {
   VALUE psych     = rb_define_module("Psych");
@@ -228,4 +244,5 @@ void Init_psych_emitter()
   rb_define_method(cPsychEmitter, "end_sequence", end_sequence, 0);
   rb_define_method(cPsychEmitter, "start_mapping", start_mapping, 4);
   rb_define_method(cPsychEmitter, "end_mapping", end_mapping, 0);
+  rb_define_method(cPsychEmitter, "alias", alias, 1);
 }
diff --git a/lib/psych/visitors/emitter.rb b/lib/psych/visitors/emitter.rb
index 966a09e..3e33095 100644
--- a/lib/psych/visitors/emitter.rb
+++ b/lib/psych/visitors/emitter.rb
@@ -32,6 +32,10 @@ module Psych
         o.children.each { |c| c.accept self }
         @handler.end_mapping
       end
+
+      visitor_for(Nodes::Alias) do |o|
+        @handler.alias o.anchor
+      end
     end
   end
 end
diff --git a/test/visitors/test_emitter.rb b/test/visitors/test_emitter.rb
index 6f19df9..e79a7b5 100644
--- a/test/visitors/test_emitter.rb
+++ b/test/visitors/test_emitter.rb
@@ -89,6 +89,21 @@ module Psych
         assert_match(/key: value/, @io.string)
         assert_equal @io.string, s.to_yaml
       end
+
+      def test_alias
+        s       = Nodes::Stream.new
+        doc     = Nodes::Document.new
+        mapping = Nodes::Mapping.new
+        mapping.children << Nodes::Scalar.new('key', 'A')
+        mapping.children << Nodes::Alias.new('A')
+        doc.children << mapping
+        s.children << doc
+
+        @visitor.accept s
+
+        assert_match(/&A key: \*A/, @io.string)
+        assert_equal @io.string, s.to_yaml
+      end
     end
   end
 end
-- 
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