[BUG]: Constant resolution issue with rails runner and datadog 2.19.0

[jonswar]

Tracer Version(s)

2.19.0

Ruby Version(s)

ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [arm64-darwin22]

Relevent Library and Version(s)

No response

Bug Report

After upgrading to Datadog 2.19.0, there's an issue with constant resolution when using rails runner to execute Ruby files. The issue occurs when a script tries to reference constants defined within a module namespace that were loaded during Rails initialization.

The issue appears to be related the patching of Kernel.load. If I comment out lines 78-110 of lib/datadog/tracing/contrib/rails/runner.rb, the bug goes away.

Reproduction Code

1. Create a new Rails application:

rails new bug --minimal

2. Add datadog 2.18.0 to the Gemfile:

gem 'datadog', '2.18.0'

3. Create a file config/initializers/datadog.rb:

require 'datadog/tracing'

Datadog.configure do |c|
  c.tracing.instrument :rails
end

4. Create a file config/initializers/example_module.rb:

module ExampleNamespace
  module Jobs
  end
end

5. Create a file lib/tasks/example_task.rb:

module ExampleNamespace
  puts Jobs.name
end

6. Run the task, it should print "ExampleNamespace::Jobs":

bundle exec rails runner lib/tasks/example_task.rb

7. Upgrade to datadog 2.19.0 in Gemfile

gem 'datadog', '2.18.0'

8. Run the task, it should fail:

bundle exec rails runner lib/tasks/example_task.rb

Configuration Block

See above

Error Logs

N/A

Operating System

Darwin Kernel Version 24.5.0 (but also repro'd on Linux)

How does Datadog help you?

No response

[ivoanjo]

Hey! Thanks for the great report. If you have it around still, it would be great to have a backtrace of when the issue happens :)

For @marcotc: This does seem to be a recent regression since #4681 was where we introduced this?

[jonswar]

Sure.

% bundle exec rails runner lib/tasks/example_task.rb
/Users/jonathanswartz/work/insta/projects/2025/2025-06-25-tracing/bug/lib/tasks/example_task.rb:2:
in `<module:ExampleNamespace>': uninitialized constant #<Module:0x00000001248d9260>::ExampleNamespace::Jobs (NameError)

  puts Jobs.name  # Should find ExampleNamespace::Jobs but fails
       ^^^^
	from /Users/jonathanswartz/work/insta/projects/2025/2025-06-25-tracing/bug/lib/tasks/example_task.rb:1:in `<top (required)>'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/datadog-2.19.0/lib/datadog/tracing/contrib/rails/runner.rb:108:in `load'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/datadog-2.19.0/lib/datadog/tracing/contrib/rails/runner.rb:108:in `block in load'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/datadog-2.19.0/lib/datadog/tracing/trace_operation.rb:241:in `block in measure'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/datadog-2.19.0/lib/datadog/tracing/span_operation.rb:167:in `measure'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/datadog-2.19.0/lib/datadog/tracing/trace_operation.rb:241:in `measure'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/datadog-2.19.0/lib/datadog/tracing/tracer.rb:424:in `start_span'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/datadog-2.19.0/lib/datadog/tracing/tracer.rb:166:in `block in trace'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/datadog-2.19.0/lib/datadog/tracing/context.rb:45:in `activate!'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/datadog-2.19.0/lib/datadog/tracing/tracer.rb:165:in `trace'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/datadog-2.19.0/lib/datadog/tracing.rb:29:in `trace'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/datadog-2.19.0/lib/datadog/tracing/contrib/rails/runner.rb:91:in `load'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/railties-7.2.2.2/lib/rails/commands/runner/runner_command.rb:44:in `block in perform'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/activesupport-7.2.2.2/lib/active_support/execution_wrapper.rb:91:in `wrap'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/railties-7.2.2.2/lib/rails/commands/runner/runner_command.rb:70:in `conditional_executor'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/railties-7.2.2.2/lib/rails/commands/runner/runner_command.rb:43:in `perform'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/thor-1.4.0/lib/thor/command.rb:28:in `run'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/thor-1.4.0/lib/thor/invocation.rb:127:in `invoke_command'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/railties-7.2.2.2/lib/rails/command/base.rb:178:in `invoke_command'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/thor-1.4.0/lib/thor.rb:538:in `dispatch'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/railties-7.2.2.2/lib/rails/command/base.rb:73:in `perform'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/railties-7.2.2.2/lib/rails/command.rb:71:in `block in invoke'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/railties-7.2.2.2/lib/rails/command.rb:149:in `with_argv'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/railties-7.2.2.2/lib/rails/command.rb:69:in `invoke'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/gems/3.3.0/gems/railties-7.2.2.2/lib/rails/commands.rb:18:in `<top (required)>'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/3.3.0/bundled_gems.rb:74:in `require'
	from /Users/jonathanswartz/.rbenv/versions/3.3.0/lib/ruby/3.3.0/bundled_gems.rb:74:in `block (2 levels) in replace_require'
	from bin/rails:4:in `<main>'

[vpellan]

Hello @jonswar ! Thank you for your report and for providing such detailed steps to reproduce this bug, we've been able to quickly find the cause of the issue and we are working on a fix. I will give you an update once we release it

[vpellan]

Hello @jonswar ! We've merged the fix PR (#4863) and it will be available in the next release ! We'll let you know once it's released ! Thanks !

[jonswar]

Great, thank you!