fix:Convert custom setting value to string for startup log

CHANGELOG.md

@@ -14,7 +14,7 @@ Git diff: https://github.com/DataDog/dd-trace-rb/compare/v0.37.0...v0.38.0
 - Kafka integration (#1070) (@tjwp)
 - Span#set_tags (#1081) (@DocX)
 - retry_count tag for Sidekiq jobs (#1089) (@elyalvarado)
-- Startup environment log (#1104)
+- Startup environment log (#1104, #1109)
 - DD_SITE and DD_API_KEY configuration (#1107)
 
 ### Changed

lib/ddtrace/diagnostics/environment_logger.rb

@@ -262,7 +262,9 @@ def instrumented_integrations_settings
           integration.configuration.to_h.flat_map do |setting, value|
             next [] if setting == :tracer # Skip internal Ruby objects
 
-            [[:"integration_#{name}_#{setting}", value]]
+            # Convert value to a string to avoid custom #to_json
+            # handlers possibly causing errors.
+            [[:"integration_#{name}_#{setting}", value.to_s]]
           end
         end]
       end

spec/ddtrace/diagnostics/environment_logger_spec.rb

@@ -246,11 +246,19 @@
         context 'with integration-specific settings' do
           let(:options) { { service_name: 'my-http' } }
 
-          it { is_expected.to include integration_http_analytics_enabled: false }
-          it { is_expected.to include integration_http_analytics_sample_rate: 1.0 }
+          it { is_expected.to include integration_http_analytics_enabled: 'false' }
+          it { is_expected.to include integration_http_analytics_sample_rate: '1.0' }
           it { is_expected.to include integration_http_service_name: 'my-http' }
-          it { is_expected.to include integration_http_distributed_tracing: true }
-          it { is_expected.to include integration_http_split_by_domain: false }
+          it { is_expected.to include integration_http_distributed_tracing: 'true' }
+          it { is_expected.to include integration_http_split_by_domain: 'false' }
+        end
+
+        context 'with a complex setting value' do
+          let(:options) { { service_name: Class.new } }
+
+          it 'converts to a string' do
+            is_expected.to include integration_http_service_name: start_with('#<Class:')
+          end
         end
       end