Merge pull request #515 from ruby/quote-y-n

Add quotes to the strings "y" and "n"

lib/psych/visitors/yaml_tree.rb

@@ -272,6 +272,8 @@ def visit_String o
           tag   = 'tag:yaml.org,2002:str'
           plain = false
           quote = false
+        elsif o == 'y' || o == 'n'
+          style = Nodes::Scalar::DOUBLE_QUOTED
         elsif @line_width && o.length > @line_width
           style = Nodes::Scalar::FOLDED
         elsif o =~ /^[^[:word:]][^"]*$/

test/psych/test_string.rb

@@ -17,6 +17,19 @@ def initialize
       end
     end
 
+    # 'y' and 'n' are kind of ambiguous.  Syck treated y and n literals in
+    # YAML documents as strings.  But this is not what the YAML 1.1 spec says.
+    # YAML 1.1 says they should be treated as booleans.  When we're dumping
+    # documents, we know it's a string, so adding quotes will eliminate the
+    # "ambiguity" in the emitted document
+    def test_y_is_quoted
+      assert_match(/"y"/, Psych.dump("y"))
+    end
+
+    def test_n_is_quoted
+      assert_match(/"n"/, Psych.dump("n"))
+    end
+
     def test_string_with_newline
       assert_equal "1\n2", Psych.load("--- ! '1\n\n  2'\n")
     end