fix: remove call to ActiveSupport::Notifications.notifier#synchronize…

… deprecated in Rails 7.2 (#707)

* wrap call to depcrecated private API behind version conditional

* convert Rails version string to Gem::Version

* fix module access?

* check for synchronize method instead of Rails version

* add comment

---------

Co-authored-by: Ariel Valentin <arielvalentin@users.noreply.github.com>

instrumentation/active_support/lib/opentelemetry/instrumentation/active_support/span_subscriber.rb

@@ -30,19 +30,23 @@ def self.subscribe(
 
         subscriber_object = ::ActiveSupport::Notifications.subscribe(pattern, subscriber)
 
-        ::ActiveSupport::Notifications.notifier.synchronize do
-          subscribers = ::ActiveSupport::Notifications.notifier.instance_variable_get(:@string_subscribers)[pattern]
-
-          if subscribers.nil?
-            OpenTelemetry.handle_error(
-              message: 'Unable to move OTEL ActiveSupport Notifications subscriber to the front of the notifications list which may cause incomplete traces.' \
-                       'Please report an issue here: ' \
-                       'https://github.com/open-telemetry/opentelemetry-ruby-contrib/issues/new?labels=bug&template=bug_report.md&title=ActiveSupport%20Notifications%20subscribers%20list%20is%20nil'
-            )
-          else
-            subscribers.unshift(
-              subscribers.delete(subscriber_object)
-            )
+        # this can be removed once we drop support for Rails < 7.2
+        # see https://github.com/open-telemetry/opentelemetry-ruby-contrib/pull/707 for more context    
+        if ::ActiveSupport::Notifications.notifier.respond_to?(:synchronize)
+          ::ActiveSupport::Notifications.notifier.synchronize do
+            subscribers = ::ActiveSupport::Notifications.notifier.instance_variable_get(:@string_subscribers)[pattern]
+
+            if subscribers.nil?
+              OpenTelemetry.handle_error(
+                message: 'Unable to move OTEL ActiveSupport Notifications subscriber to the front of the notifications list which may cause incomplete traces.' \
+                         'Please report an issue here: ' \
+                         'https://github.com/open-telemetry/opentelemetry-ruby-contrib/issues/new?labels=bug&template=bug_report.md&title=ActiveSupport%20Notifications%20subscribers%20list%20is%20nil'
+              )
+            else
+              subscribers.unshift(
+                subscribers.delete(subscriber_object)
+              )
+            end
           end
         end
         subscriber_object