[PROF-3514] Skip CPU time instrumentation if logging gem is detected

This is a repeat of #1362 -- the logging gem also monkey patches
`Thread` initialization using `alias_method`, which is incompatible
with our instrumentation that uses `preload`.

For details, see TwP/logging#230 where we
submitted a fix to the upstream gem.

Right now the only way to avoid this issue and still enable proflier is
to either remove the logging gem or to disable the feature using the
`LOGGING_INHERIT_CONTEXT` environment variable.

If/when the gem creators accept our proposed change and release it,
we'll need to revise this to take that into consideration, as we do
for rollbar.

NOTE: I'm not entirely happy with the complexity that is accumulating
for the tests, but I've decided to not refactor it yet. If we need
to add more gems, we should definitely refactor the tests. My hope is
that soon we can get rid of our `Thread` monkey patches, and thus get
rid of all of this instead.

Author: ivoanjo

lib/ddtrace/profiling/ext/cpu.rb

@@ -44,8 +44,23 @@ def self.unsupported_reason
             'You have an incompatible rollbar gem version installed; ensure that you have rollbar >= 3.1.2 by ' \
             "adding `gem 'rollbar', '>= 3.1.2'` to your Gemfile or gems.rb file. " \
             'See https://github.com/rollbar/rollbar-gem/pull/1018 for details.'
+          elsif Gem::Specification.find_all_by_name('logging').any? && logging_inherit_context_enabled?
+            "Feature is incompatible with the `logging` gem's thread inherit context feature. " \
+            "Please add LOGGING_INHERIT_CONTEXT=false to your application's environment variables to disable the " \
+            'conflicting feature. ' \
+            'See https://github.com/TwP/logging/pull/230 for details.'
           end
         end
+
+        private_class_method def self.logging_inherit_context_enabled?
+          # The logging gem provides a mechanism to disable the conflicting behavior, see
+          # https://github.com/TwP/logging/blob/ae9872d093833b2a5a34cbe1faa4e895a81f6845/lib/logging/diagnostic_context.rb#L418
+          # Here we check if the behavior is enabled
+          inherit_context_configuration = ENV['LOGGING_INHERIT_CONTEXT']
+
+          inherit_context_configuration.nil? ||
+          (inherit_context_configuration && !%w[false no 0].include?(inherit_context_configuration.downcase))
+        end
       end
     end
   end

spec/ddtrace/profiling/ext/cpu_spec.rb

@@ -77,7 +77,51 @@
               .and_return([])
           end
 
-          it { is_expected.to be nil }
+          context 'when logging gem is installed' do
+            before do
+              expect(Gem::Specification)
+                .to receive(:find_all_by_name)
+                .with('logging')
+                .and_return([instance_double(Gem::Specification)])
+            end
+
+            around do |example|
+              ClimateControl.modify('LOGGING_INHERIT_CONTEXT' => logging_inherit_context) do
+                example.run
+              end
+            end
+
+            context 'when no LOGGING_INHERIT_CONTEXT is defined' do
+              let(:logging_inherit_context) { nil }
+
+              it { is_expected.to include 'incompatible with the `logging` gem' }
+            end
+
+            context 'when LOGGING_INHERIT_CONTEXT is set to any value other than false/no/0 (case-insensitive)' do
+              let(:logging_inherit_context) { 'YesPlease' }
+
+              it { is_expected.to include 'incompatible with the `logging` gem' }
+            end
+
+            context 'when LOGGING_INHERIT_CONTEXT is set to false/no/0 (case-insensitive)' do
+              %w[false no FaLsE nO 0].each do |disabled_setting|
+                let(:logging_inherit_context) { disabled_setting }
+
+                it { is_expected.to be nil }
+              end
+            end
+          end
+
+          context 'when logging gem is not installed' do
+            before do
+              expect(Gem::Specification)
+                .to receive(:find_all_by_name)
+                .with('logging')
+                .and_return([])
+            end
+
+            it { is_expected.to be nil }
+          end
         end
       end
     end