Add conditional for when formatting metric name symbol (#297)

* Add conditional

* Use RUBY_VERSION

* feedback

lib/datadog/statsd/serialization/stat_serializer.rb

@@ -37,9 +37,18 @@ def global_tags
         attr_reader :prefix
         attr_reader :tag_serializer
 
-        def formatted_metric_name(metric_name)
-          formatted = Symbol === metric_name ? metric_name.name : metric_name.to_s
+        if RUBY_VERSION < '3'
+          def metric_name_to_string(metric_name)
+            metric_name.to_s
+          end
+        else
+          def metric_name_to_string(metric_name)
+            Symbol === metric_name ? metric_name.name : metric_name.to_s
+          end
+        end
 
+        def formatted_metric_name(metric_name)
+          formatted = metric_name_to_string(metric_name)
           if formatted.include?('::')
             formatted = formatted.gsub('::', '.')
             formatted.tr!(':|@', '_')

spec/statsd/serialization/stat_serializer_spec.rb

@@ -108,6 +108,18 @@
         expect(input).to eq 'somecount:|@test'
       end
     end
+
+    context "when metric name is a symbol" do
+      it 'formats correctly without error' do
+        input = :'somecount::test'
+        output = subject.format(input, 1, 'c')
+        expect(output).to eq 'somecount.test:1|c'
+
+        input = :'somecount:|@test'
+        output = subject.format(input, 1, 'c')
+        expect(output).to eq 'somecount___test:1|c'
+      end
+    end
   end
 
   context 'benchmark' do