Defer agent initialization in Rails until after :load_config_initializers #1658
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kaylareopelle
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Previously, ActionView was forced to load by the agent before ActiveSupport loaded its code, causing any application-defined initializers related to ActionView to be ignored. Subscribing after ActiveSupport loads ActionView resolves the problem.
The central argument around loading the agent before other initializers is to allow initializers to reference the add_method_tracer API. Including the modules before other initializers are run allows this to happen. If the second initializer doesn't specify when it should be run, it will run immediately after our first initializer. By specifying after: :load_config_initializers, the agent will not execute init_plugin until after initializers defined in config/initializers are run. This stops the agent from forcing ActiveRecord to load before customer-defined initializers.
The previous instructions were not compatible with Zsh. These instructions work with Zsh and bash.
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Starting the agent after :load_config_initializers prevents the dynamic initializer for roadie-rails from running, making the gem moot. The customer who used the bugfix also had an error pop up with one of their initializers. Though this change solves the problem with configs getting applied, it may interact unpredictably with existing initializers. We won't turn on this behavior by default until a major version release.
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For Rails applications, the agent initialized before all other initializers with the
before: :load_config_initializershook.Though this enables initializers to reference the
add_method_tracerAPI, there are actions within the agent's initialization that load Rails framework libraries (ActiveJob, ActiveRecord, ActionView). This caused initializers referencing these libraries to be skipped entirely.Since we only need the
add_method_tracerAPI to be available before the initializers are run, the modules that include this API will be loaded before config initializers. All other agent-initialization activity will be loaded after config initializers.Furthermore, ActionView was the only Rails framework library that did not have an
ActiveSupport.on_loadblock around the instrumentation executes block. This has been added.Closes #662