Ensure strings that may be confused as YAML1.2 numbers are quoted

lib/psych/visitors/yaml_tree.rb

@@ -274,7 +274,7 @@ def visit_String o
           style = Nodes::Scalar::FOLDED
         elsif o.match?(/^[^[:word:]][^"]*$/)
           style = Nodes::Scalar::DOUBLE_QUOTED
-        elsif not String === @ss.tokenize(o) or /\A0[0-7]*[89]/.match?(o)
+        elsif not String === @ss.tokenize(o) or may_be_confused_as_yaml12?(o)
           style = Nodes::Scalar::SINGLE_QUOTED
         end
 
@@ -388,6 +388,19 @@ def binary? string
         string.encoding == Encoding::ASCII_8BIT && !string.ascii_only?
       end
 
+      def may_be_confused_as_yaml12? string
+        case string
+        when /\A0[0-7]*[89]\z/ # YAML 1.1 int (Base 8)
+          true
+        when /\A0o[0-7]+\z/ # YAML 1.2 int (Base 8)
+          true
+        when /\A[-+]?(\.[0-9]+|[0-9]+(\.[0-9]*)?)([eE][-+]?[0-9]+)?\z/ # YAML 1.1/1.2 float (Number)
+          true
+        else
+          false
+        end
+      end
+
       def visit_array_subclass o
         tag = "!ruby/array:#{o.class}"
         ivars = o.instance_variables

test/psych/visitors/test_yaml_tree.rb

@@ -167,9 +167,22 @@ def test_float
       end
 
       def test_string
+        # YAML 1.1 int Base 8
         assert_include(Psych.dump({'a' => '017'}), "'017'")
         assert_include(Psych.dump({'a' => '019'}), "'019'")
         assert_include(Psych.dump({'a' => '01818'}), "'01818'")
+
+        # YAML 1.1 float Number
+        assert_include(Psych.dump({'a' => '.2e3'}), '".2e3"')
+
+        # YAML 1.2 int Base 8
+        assert_include(Psych.dump({'a' => '0o17'}), "'0o17'")
+        assert_include(Psych.dump({'a' => '0o111'}), "'0o111'")
+
+        # YAML 1.2 float Number
+        assert_include(Psych.dump({'a' => '12e03'}), "'12e03'")
+        assert_include(Psych.dump({'a' => '0e447890'}), "'0e447890'")
+        assert_include(Psych.dump({'a' => '1.2e3'}), "'1.2e3'")
       end
 
       # http://yaml.org/type/null.html