WIP: Add disallow_deprecation_warnings:rails

[george-ma]

What are you trying to accomplish?

This work is a follow up of deprecation work handling the new Rails.application.deprecation for our Rails Upgrade script. We discussed that it would be nice to have a way to only configure the deprecations from Rails within an application as its those (Rails) deprecations that would need to be actioned on during a Rails upgrade.

Example of this working with the following test:

### In `test.rb`
config.active_support.disallowed_deprecation = :raise
config.active_support.disallowed_deprecation_warnings = :rails

### test/models/rails_deprecation_test.rb
# frozen_string_literal: true

require "test_helper"

class RailsDeprecationTest < ActiveSupport::TestCase
  test "deprecation warning from Rails" do
    ActionController::Parameters.new == {}
  end

  test "deprecation warning from a gem unrelated to Rails" do
    Rails.application.deprecators[:some_gem].warn("this is deprecated")
  end
end

1 deprecation from Rails, 1 deprecation defined in the sandbox itself- notice how only the deprecation from rails is "raised" as an error.

Work remaining:

• Edit the docs guides/source/configuring.md; specifically, the config.active_support_disallowed_deprecation_warnings section to include mention of :all and :rails

What should reviewers focus on?

Before you deploy

• I tophatted or tested this change. (tested on my own sandbox repo)
• This PR is safe to rollback.

[jonathanhefner]

I agree this would be a nice feature! 😃

I like that the implementation is compact, but from an architectural standpoint, it feels a little odd to handle this from inside the deprecator. What I mean is, the way I would accomplish this without any special API would be something like:

Rails.application.deprecators.each do |deprecator|
  deprecator.disallowed_warnings = :all if deprecator.gem_name == "Rails"
end

To bridge the gap between that and config.active_support.disallowed_deprecation_warnings = :rails, perhaps we could introduce a Deprecators#disallow_warnings_from method:

# Could also accept a pattern (e.g. `/rails/i`) or multiple args
Rails.application.deprecators.disallow_warnings_from("Rails")

Then we could potentially add a config.active_support.disallow_warnings_from config setting. Though there might be a better / more consistent name.

Thoughts?

[jonathanhefner]

perhaps we could introduce a Deprecators#disallow_warnings_from method

Or another possibility would be to add a Deprecators#disallow_warnings method with a :from or :gem option:

# Could also accept a pattern (e.g. `/rails/i`)
Rails.application.deprecators.disallow_warnings(gem: "Rails")

Afterward, we could add a matching option to #silence, e.g.:

Rails.application.deprecators.silence(gem: "Rails") do 
  # ...
end

[george-ma]

👋🏻 appreciate the fast feedback! Fair point about the architectural awkwardness, I like the second option and will explore it asap!

[etiennebarrie]

the way I would accomplish this without any special API would be something like

Oh yeah that would totally work and require no additional API. Given rails#46550 we should be able to do that in config/environments/production.rb and have all the Rails deprecators ready to be configured.

[george-ma]

Will close for now as we will go with that no-api approach. Will revisit in the future if there is a need for other gems to be deprecated!