Cannot inject behavior into assets.context_class when precompiling assets.

[bhaibel]

I'm mixing Rails helpers into my sprockets context per the documentation here:

https://github.com/rails/sprockets/blob/master/lib/sprockets/context.rb#L6-L18

This is happening in a Rails.application.config.after_initialize block. So something like this

Rails.application.config.after_initialize do
  Rails.application.assets.context_class.class_eval do
    include RailsViewHelperStuff
  end
end

When I precompile assets in the development rails env, this works fine. However, once I start working in an env where Rails.application.config.assets.compile is false, I get a NoMethodError: undefined methodcontext_class' for nil:NilClass`.

This appears to be a side effect of #220, which stopped building Rails.application.assets when Rails.application.config.assets.compile was false. Because y'all merged #222, I'm guessing that breaking precompilation in this case was an accident rather than you intentionally deprecating the context_class injection interface.

[bhaibel]

I'm guessing this could be trivially fixed by moving the build_environment here:

https://github.com/rails/sprockets-rails/blob/master/lib/sprockets/railtie.rb#L164

outside of the if statement, but that doesn't sound like it's within the spirit of #220.

[rafaelfranca]

You should not use a after_initialize block. Use a configure block that is the correct way to configure the assets pipeline:

Rails.application.config.assets.configure do |env|
  env.context_class.class_eval do
    include RailsViewHelperStuff
  end
end