TaggedLogging to return a new logger instance

[tjoyal]

Summary

I have a small question and what is better than a PR to discuss it.

ActiveSupport::TaggedLogging through the new method would mutate the argument instead of returning a new instance. This might be my design but it really got me confused at first. I would have expected some other kind of method to provide such mutation (eg.: ActiveSupport::TaggedLogging.tag(logger))

The changes in here would clone the logger received in argument (and the associated formatter that ActiveSupport::TaggedLogging perform on) returning a new instance.

The associated test is what made me really confused the first time I hit the original behaviour.

Todo:

• If this go forward it'll require an entry in changelog?

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[arthurnn]

I agree that new should return a new object, and not mutate the existent one.
@rafaelfranca @matthewd thoughts?
I am 👍 here

[rafaelfranca]

LGTM too. A CHANGELOG entry will be required since this may be a breaking change.

[rafaelfranca]

Those lines should be aligned with the if. Rubocop is complaining.

[tjoyal]

Updated, tell me if you are good with the changes.

[matthewd]

Does this risk multiplying the number of live logger instances we have in an application?

That seems like it could affect what gets silenced, for example.

[tjoyal]

Does this risk multiplying the number of live logger instances we have in an application?

My thought of chain on this is when calling new, I expect to get a new object.

I think it's a fair concern, and to some extent I would consider setting my Rails.logger to return a tagged logger from the ground up if I was planning to tag a lot of things. (vs re-init everywhere in the code leading to a lot of code duplication).

I think it would be possible to come up with a mutating method that is not named new that would have the old behaviour, but I don't see the need for it just yet.

That seems like it could affect what gets silenced, for example.

Definitely (it's a new instance after all, unless dup decide to handle logic to bridge behaviour between instances).

But once again, I think this is expected from a method that is called new.

As proposed up there, if one was to use a lot of tagged logging in his application, I think it would be fair to consider setting it as the default logger.

In the cases where I wanted to use tagged logging, the desired behaviour was to do a dup like in this PR so my tags are only applied to the current context of the unit of code I'm wrapping, and not propagated to other unit of code that might be called in other classes.

Eg.: A fairly simple example

class Object
  def method_a
    logger = ActiveSupport::TaggedLogging.new(Rails.logger)
    logger.tagged("BCX") do
      logger.info "something" # I expected this to be tagged
      method_b
    end
  end

  def method_b
    Rails.logger.info "something else" # I do not expect this to be tagged
  end
end

[gmcgibbon]

Still relevant in Rails 6 28e5085. I'll admit that when I first saw the source for ActiveSupport::TaggedLogging.new I thought it was being too clever. If we want to keep the mutation approach, could we just rename the new method to something more explanatory?

[orhantoy]

Any special reason #dup was used here? I have opened #40759 to address a side-effect of not using #clone.