sentry-rails triggers "Prematurely executing load hooks" warning for :action_dispatch_response on Rails 8.2

[aviflombaum]

Issue Description

sentry-rails triggers a "Prematurely executing load hooks" deprecation warning on boot with Rails 8.2 (edge). The warning is about :action_dispatch_response being loaded before application initialization completes.

The root cause is in Sentry::Railtie#extend_controller_methods (sentry-rails/lib/sentry/rails/railtie.rb:95). Inside the ActiveSupport.on_load :action_controller block, the line:

ActionController::Live.send(:prepend, Sentry::Rails::Overrides::StreamingReporter)

forces eager loading of ActionController::Live, which requires action_controller/metal/live.rb, which in turn requires action_dispatch/http/response.rb. That file calls ActiveSupport.run_load_hooks(:action_dispatch_response, ...), triggering the :action_dispatch_response load hook prematurely during the after_initialize phase.

Rails 8.2 added detection for this pattern and emits the warning.

Full Stack Trace

/activesupport/lib/active_support/lazy_load_hooks.rb:97:in 'Module#class_eval'
/activesupport/lib/active_support/lazy_load_hooks.rb:97:in 'block in ActiveSupport::LazyLoadHooks#execute_hook'
/activesupport/lib/active_support/lazy_load_hooks.rb:87:in 'ActiveSupport::LazyLoadHooks#with_execution_control'
/activesupport/lib/active_support/lazy_load_hooks.rb:92:in 'ActiveSupport::LazyLoadHooks#execute_hook'
/activesupport/lib/active_support/lazy_load_hooks.rb:78:in 'block in ActiveSupport::LazyLoadHooks#run_load_hooks'
/activesupport/lib/active_support/lazy_load_hooks.rb:77:in 'ActiveSupport::LazyLoadHooks#run_load_hooks'
/actionpack/lib/action_dispatch/http/response.rb:603:in '<module:ActionDispatch>'
/actionpack/lib/action_dispatch/http/response.rb:10:in '<main>'
/action_controller/metal/live.rb:5:in '<main>'
/sentry-rails-6.5.0/lib/sentry/rails/railtie.rb:95:in 'block in Sentry::Railtie#extend_controller_methods'
/sentry-rails-6.5.0/lib/sentry/rails/railtie.rb:92:in 'ActiveSupport::LazyLoadHooks#on_load'
/sentry-rails-6.5.0/lib/sentry/rails/railtie.rb:46:in 'block in <class:Railtie>'

Reproduction Steps

1. Create a Rails 8.2 (edge/alpha) application with sentry-rails 6.5.0
2. Configure Sentry in an initializer (any config, even minimal)
3. Boot the application in an environment where Sentry.init is called (e.g. production, staging) — rails server, rails console, or any rake task
4. Observe the warning in output:

:action_dispatch_response was loaded before application initialization.
Prematurely executing load hooks will slow down your boot time
and could cause conflicts with the load order of your application.
Please wrap your code with an on_load hook:

  ActiveSupport.on_load(:action_dispatch_response) do
    # your code here
  end

The warning only appears when Sentry.initialized? is true, since the extend_controller_methods call in config.after_initialize is guarded by that check (railtie.rb:41). Environments where Sentry.init is not called (e.g. development) do not trigger the warning.

Expected Behavior

No premature load hook warning on boot. The ActionController::Live prepend should be deferred to avoid triggering early loading of ActionDispatch::Response.

Actual Behavior

The deprecation warning is emitted on every boot in environments where Sentry is initialized (server start, console, rake tasks in production/staging).

Suggested Fix

Move the ActionController::Live prepend into its own lazy load hook to avoid eagerly loading it inside :action_controller. For example:

def extend_controller_methods
  require "sentry/rails/controller_methods"
  require "sentry/rails/controller_transaction"
  require "sentry/rails/overrides/streaming_reporter"

  ActiveSupport.on_load :action_controller do
    include Sentry::Rails::ControllerMethods
    include Sentry::Rails::ControllerTransaction
  end

  ActiveSupport.on_load :action_controller do
    ActionController::Live.send(:prepend, Sentry::Rails::Overrides::StreamingReporter)
  end
end

Or alternatively, guard the prepend with a lazy reference that doesn't trigger autoloading until ActionController::Live is actually used.

Ruby Version

4.0.2

SDK Version

sentry-ruby 6.5.0, sentry-rails 6.5.0

Integration and Its Version

Rails 8.2.0.alpha (edge, commit 4df808965b4a)

Sentry Config

Sentry.init do |config|
  config.dsn = "..."
  config.breadcrumbs_logger = [:active_support_logger, :http_logger]
  config.traces_sample_rate = 0.1
  config.environment = Rails.env
  config.enabled_environments = %w[production staging]
end

[linear-code]

RUBY-163