[PROF-10015] Fix Phusion Passenger detection when not in Gemfile/gems.rb

lib/datadog/profiling/component.rb

@@ -397,8 +397,12 @@ def self.build_profiler_component(settings:, agent_settings:, optional_tracer:)
 
       # See https://github.com/datadog/dd-trace-rb/issues/2976 for details.
       private_class_method def self.incompatible_passenger_version?
+        first_compatible_version = Gem::Version.new('6.0.19')
+
         if Gem.loaded_specs['passenger']
-          Gem.loaded_specs['passenger'].version < Gem::Version.new('6.0.19')
+          Gem.loaded_specs['passenger'].version < first_compatible_version
+        elsif defined?(PhusionPassenger::VERSION_STRING)
+          Gem::Version.new(PhusionPassenger::VERSION_STRING) < first_compatible_version
         else
           true
         end

spec/datadog/profiling/component_spec.rb

@@ -877,6 +877,29 @@
           end
         end
 
+        context 'when passenger gem is not available, but PhusionPassenger::VERSION_STRING is available' do
+          context 'on passenger >= 6.0.19' do
+            before { stub_const('PhusionPassenger::VERSION_STRING', '6.0.19') }
+
+            it { is_expected.to be false }
+          end
+
+          context 'on passenger < 6.0.19' do
+            before do
+              stub_const('PhusionPassenger::VERSION_STRING', '6.0.18')
+              allow(Datadog.logger).to receive(:warn)
+            end
+
+            it { is_expected.to be true }
+
+            it 'logs a warning message mentioning that the no signals workaround is going to be used' do
+              expect(Datadog.logger).to receive(:warn).with(/Enabling the profiling "no signals" workaround/)
+
+              no_signals_workaround_enabled?
+            end
+          end
+        end
+
         context 'when mysql2 / rugged gems + passenger are not available' do
           include_context('loaded gems', passenger: nil, mysql2: nil, rugged: nil)
 

vendor/rbs/passenger/0/passenger.rbs

@@ -1,2 +1,3 @@
 module PhusionPassenger
+  VERSION_STRING: ::String
 end