feat: Workaround tagged_logging bug in Rails 7.0.3

Signed-off-by: Ferenc Géczi <[email protected]>

gemfiles/rails_70.gemfile

@@ -8,7 +8,7 @@ gem "puma"
 gem "rack-test"
 gem "simplecov", "~> 0.21.2"
 gem "mail", ">= 2.8.1"
-gem "rails", "7.0.8"
+gem "rails", "7.0.3"
 gem "mysql2", "0.5.5"
 gem "pg"
 gem "sqlite3", "~> 1.4"

lib/instana/frameworks/rails.rb

@@ -18,6 +18,28 @@ class Railtie < ::Rails::Railtie
         if ::Instana.config[:logging][:enabled] && !ENV.key?('INSTANA_TEST')
           logger = ::Instana::InstrumentedLogger.new('/dev/null')
           if ::Rails::VERSION::STRING < "7.1"
+            # Rails 7.0.3 `tagged_logging.rb` has a number of bugs.
+            # What pertains to our instrumentation here is that in
+            # https://github.com/rails/rails/blob/v7.0.3/activesupport/lib/active_support/tagged_logging.rb#L100
+            # sets the `other_logger.formatter` to `formatter` if `other_logger.formatter` is `nil`
+            # but then
+            # https://github.com/rails/rails/blob/v7.0.3/activesupport/lib/active_support/tagged_logging.rb#L102
+            # redefines `formatter.current_tags` method to a proc calling `formatter.current_tags`, itself.
+            # which is an infinite recursion.
+            #
+            # This bug starts with 7.0.3:
+            # https://github.com/rails/rails/compare/v7.0.2...v7.0.3#diff-68f90ba4998610be2f7da027e006e8ddeeb06dece66f41579c94070e12f23011
+            # And is already reverted/fixed in 7.0.4
+            # https://github.com/rails/rails/compare/v7.0.3...v7.0.4#diff-68f90ba4998610be2f7da027e006e8ddeeb06dece66f41579c94070e12f23011
+            # The commit which fixes it is:
+            # https://github.com/rails/rails/commit/ff277583e22ddfbcfbd2131789a7cb7c2f868d68
+            #
+            # Since instana does trigger this bug here we workaround it, by defining the `formatter`,
+            # to break the infinite loop. The `formatter` used here is the same as the default used in
+            # https://github.com/rails/rails/blob/v7.0.3/activesupport/lib/active_support/tagged_logging.rb#L89C9-L89C70
+            if ::Rails::VERSION::STRING == "7.0.3"
+              logger.formatter = ActiveSupport::Logger::SimpleFormatter.new
+            end
             Rails.logger.extend(ActiveSupport::Logger.broadcast(logger))
           else
             Rails.logger.broadcast_to(logger)