WIP: baggage span tags

[rachelyangdog]

What does this PR do?

Motivation:

Change log entry

Additional Notes:

How to test the change?

[github-actions]

👋 Hey @DataDog/ruby-guild, please fill "Change log entry" section in the pull request description.

If changes need to be present in CHANGELOG.md you can state it this way

**Change log entry**

Yes. A brief summary to be placed into the CHANGELOG.md

(possible answers Yes/Yep/Yeah)

Or you can opt out like that

**Change log entry**

None.

(possible answers No/Nope/None)

^{Visited at: 2025-06-05 15:22:27 UTC}

[datadog-datadog-prod-us1]

Datadog Report

Branch report: rachel.yang/baggage-span-tags
Commit report: 3595efc
Test service: dd-trace-rb

❌ 22 Failed (0 Known Flaky), 222 Passed, 0 Skipped, 8.22s Total Time

❌ Failed Tests (22)

This report shows up to 5 failed tests.

• Datadog::Tracing::Contrib::ActiveSupport::Configuration::Settings Option cache_servicewhen without service_name - rspec - Details

  Expand for error

   uninitialized constant Datadog::Tracing::Contrib::SpanAttributeSchema
   
   Failure/Error:
     Contrib::SpanAttributeSchema.fetch_service_name(
       '',
       Ext::SERVICE_CACHE
     )
   
   NameError:
     uninitialized constant Datadog::Tracing::Contrib::SpanAttributeSchema
   ...
  

• Datadog::Tracing::Contrib::ActiveSupport::Configuration::Settings Option cache_servicewhen without service_name v0 but uses env var - rspec - Details

  Expand for error

   uninitialized constant Datadog::Tracing::Contrib::SpanAttributeSchema
   
   Failure/Error:
     Contrib::SpanAttributeSchema.fetch_service_name(
       '',
       Ext::SERVICE_CACHE
     )
   
   NameError:
     uninitialized constant Datadog::Tracing::Contrib::SpanAttributeSchema
   ...
  

• Datadog::Tracing::Contrib::Dalli::Configuration::Settings behaves like service name setting Option service_namewhen without service_name v0 - rspec - Details

  Expand for error

   uninitialized constant Datadog::Tracing::Contrib::SpanAttributeSchema
   
   Failure/Error:
     Contrib::SpanAttributeSchema.fetch_service_name(
       Ext::ENV_SERVICE_NAME,
       Ext::DEFAULT_PEER_SERVICE_NAME
     )
   
   NameError:
     uninitialized constant Datadog::Tracing::Contrib::SpanAttributeSchema
   ...
  

• Datadog::Tracing::Contrib::Dalli::Configuration::Settings behaves like service name setting Option service_namewhen without service_name v0 but uses env var - rspec - Details

  Expand for error

   uninitialized constant Datadog::Tracing::Contrib::SpanAttributeSchema
   
   Failure/Error:
     Contrib::SpanAttributeSchema.fetch_service_name(
       Ext::ENV_SERVICE_NAME,
       Ext::DEFAULT_PEER_SERVICE_NAME
     )
   
   NameError:
     uninitialized constant Datadog::Tracing::Contrib::SpanAttributeSchema
   ...
  

• Datadog::Tracing::Contrib::Faraday::Configuration::Settings behaves like service name setting Option service_namewhen without service_name v0 - rspec

[marcotc]

You receive the value for baggage_span_tags in the initialize method of this class, so it doesn't have to be resolve every time. The caller then will provide the value.

[marcotc]

This kind of configuration processing should be done at the setting side, so it only needs to be done once. Take a look at after_set to see how you can manipulate the setting at declaration time:

dd-trace-rb/lib/datadog/tracing/configuration/settings.rb

Line 98 in 3595efc

o.after_set do |styles|