Fix profiler libmysqlclient version detection with mysql2-aurora gem

Steepfile

@@ -659,6 +659,7 @@ target :ddtrace do
   library 'google-protobuf'
   library 'protobuf-cucumber'
   library 'mysql2'
+  library 'mysql2-aurora'
   library 'opentracing'
   library 'concurrent-ruby'
   library 'faraday'

lib/datadog/profiling/component.rb

@@ -207,7 +207,7 @@ def self.build_profiler_component(settings:, agent_settings:, optional_tracer:)
         if Gem.loaded_specs['mysql2'] && incompatible_libmysqlclient_version?(settings)
           Datadog.logger.warn(
             'Enabling the profiling "no signals" workaround because an incompatible version of the mysql2 gem is ' \
-            'installed. Profiling data will have lower quality.' \
+            'installed. Profiling data will have lower quality. ' \
             'To fix this, upgrade the libmysqlclient in your OS image to version 8.0.0 or above.'
           )
           return true
@@ -245,9 +245,22 @@ def self.build_profiler_component(settings:, agent_settings:, optional_tracer:)
         begin
           require 'mysql2'
 
-          return true unless defined?(Mysql2::Client) && Mysql2::Client.respond_to?(:info)
-
-          libmysqlclient_version = Gem::Version.new(Mysql2::Client.info[:version])
+          # The mysql2-aurora gem likes to monkey patch itself in replacement of Mysql2::Client, and uses
+          # `method_missing` to delegate to the original BUT unfortunately does not implement `respond_to_missing?` and
+          # thus our `respond_to?(:info)` below was failing.
+          #
+          # But on the bright side, the gem does stash a reference to the original Mysql2::Client class in a constant,
+          # so if that constant exists, we use that for our probing.
+          mysql2_client_class =
+            if defined?(Mysql2::Aurora::ORIGINAL_CLIENT_CLASS)
+              Mysql2::Aurora::ORIGINAL_CLIENT_CLASS
+            elsif defined?(Mysql2::Client)
+              Mysql2::Client
+            end
+
+          return true unless mysql2_client_class && mysql2_client_class.respond_to?(:info)
+
+          libmysqlclient_version = Gem::Version.new(mysql2_client_class.info[:version])
 
           compatible = libmysqlclient_version >= Gem::Version.new('8.0.0')
 

spec/datadog/profiling/component_spec.rb

@@ -551,6 +551,32 @@
                 no_signals_workaround_enabled?
               end
             end
+
+            context 'when mysql2-aurora gem is loaded and libmysqlclient < 8.0.0' do
+              before do
+                fake_original_client = double('Fake original Mysql2::Client')
+                stub_const('Mysql2::Aurora::ORIGINAL_CLIENT_CLASS', fake_original_client)
+                expect(fake_original_client).to receive(:info).and_return({ version: '7.9.9' })
+
+                client_replaced_by_aurora = double('Fake Aurora Mysql2::Client')
+                stub_const('Mysql2::Client', client_replaced_by_aurora)
+              end
+
+              it { is_expected.to be true }
+            end
+
+            context 'when mysql2-aurora gem is loaded and libmysqlclient >= 8.0.0' do
+              before do
+                fake_original_client = double('Fake original Mysql2::Client')
+                stub_const('Mysql2::Aurora::ORIGINAL_CLIENT_CLASS', fake_original_client)
+                expect(fake_original_client).to receive(:info).and_return({ version: '8.0.0' })
+
+                client_replaced_by_aurora = double('Fake Aurora Mysql2::Client')
+                stub_const('Mysql2::Client', client_replaced_by_aurora)
+              end
+
+              it { is_expected.to be false }
+            end
           end
         end
 

vendor/rbs/mysql2-aurora/0/mysql2-aurora.rbs

@@ -0,0 +1,5 @@
+module Mysql2
+  module Aurora
+    ORIGINAL_CLIENT_CLASS: untyped
+  end
+end