[PROF-2585] Warn on incompatible rollbar version

lib/ddtrace/profiling/tasks/setup.rb

@@ -9,6 +9,7 @@ module Tasks
       # Sets up profiling for the application
       class Setup
         def run
+          check_warnings!
           activate_main_extensions
           autostart_profiler
         end
@@ -79,6 +80,22 @@ def autostart_profiler
           log "[DDTRACE] Could not autostart profiling. Cause: #{e.message} Location: #{e.backtrace.first}"
         end
 
+        def check_warnings!
+          warn_if_incompatible_rollbar_gem_detected
+        end
+
+        # See https://github.com/rollbar/rollbar-gem/pull/1018 for details on the incompatibility
+        def warn_if_incompatible_rollbar_gem_detected
+          incompatible_rollbar_versions = Gem::Requirement.new('<= 3.1.1')
+
+          if Gem::Specification.find_all_by_name('rollbar', incompatible_rollbar_versions).any?
+            log "[DDTRACE] Incompatible version of the rollbar gem is installed (#{incompatible_rollbar_versions}). " \
+              'Loading this version of the rollbar gem will disable ddtrace\'s CPU profiling. ' \
+              'Please upgrade to the latest rollbar version. ' \
+              'See https://github.com/rollbar/rollbar-gem/pull/1018 for details.'
+          end
+        end
+
         private
 
         def log(message)

spec/ddtrace/profiling/tasks/setup_spec.rb

@@ -12,6 +12,7 @@
     subject(:run) { task.run }
 
     it do
+      expect(task).to receive(:check_warnings!).ordered
       expect(task).to receive(:activate_main_extensions).ordered
       expect(task).to receive(:autostart_profiler).ordered
       run
@@ -346,4 +347,63 @@
       end
     end
   end
+
+  describe '#check_warnings!' do
+    subject(:check_warnings!) { task.check_warnings! }
+
+    it do
+      expect(task).to receive(:warn_if_incompatible_rollbar_gem_detected)
+
+      check_warnings!
+    end
+  end
+
+  describe '#warn_if_incompatible_rollbar_gem_detected' do
+    subject(:warn_if_incompatible_rollbar_gem_detected) { task.warn_if_incompatible_rollbar_gem_detected }
+
+    let(:last_version_of_rollbar_affected) { '3.1.1' }
+
+    before do
+      # Simulate the result of the gem apis, so that we can check different combinations of having or not having the
+      # rollbar gem and affected versions
+      expect(Gem::Specification)
+        .to receive(:find_all_by_name)
+        .with('rollbar', Gem::Requirement.new("<= #{last_version_of_rollbar_affected}"))
+        .and_return(rollbar_versions_found)
+    end
+
+    context 'when rollbar gem is not installed' do
+      let(:rollbar_versions_found) { [] }
+
+      it 'does not display a warning to STDOUT' do
+        expect(STDOUT).to_not receive(:puts)
+
+        warn_if_incompatible_rollbar_gem_detected
+      end
+    end
+
+    context 'when compatible version of rollbar gem is installed' do
+      # same as "no gem installed" because we use a version requirement when
+      # calling find_all_by_name, so only incompatible versions get returned
+      let(:rollbar_versions_found) { [] }
+
+      it 'does not display a warning to STDOUT' do
+        expect(STDOUT).to_not receive(:puts)
+
+        warn_if_incompatible_rollbar_gem_detected
+      end
+    end
+
+    context 'when incompatible version of rollbar gem is installed' do
+      let(:rollbar_versions_found) { [instance_double(Gem::Specification), instance_double(Gem::Specification)] }
+
+      it 'displays a warning to STDOUT' do
+        expect(STDOUT).to receive(:puts) do |message|
+          expect(message).to include('Incompatible version of the rollbar')
+        end
+
+        warn_if_incompatible_rollbar_gem_detected
+      end
+    end
+  end
 end