Issue #17122 has been updated by jeremyevans0 (Jeremy Evans).


I don't think we should add a category keyword if the only usage is for deprecation warnings. If we are going to do this, I think:

* All warning messages emitted by the core and the stdlib should have a category added
  * This requires we agree on category symbols
  * This requires new C-API warning functions added that accept a category
* Kernel#warn should accept a category keyword and pass it to Warning.warn

Having Warning.warn accept any keywords will break existing versions of the warning gem, but I can update that if this is accepted.

I don't think the benefits of adding this outweigh the cost, but I'm not strongly opposed to it.

----------------------------------------
Feature #17122: Add category to Warning#warn
https://bugs.ruby-lang.org/issues/17122#change-87054

* Author: eileencodes (Eileen Uchitelle)
* Status: Open
* Priority: Normal
----------------------------------------
Deprecation warnings and other warnings in Ruby have a category (:deprecated, etc) but those categories aren't exposed or accessible. In the most recent Ruby 2.7 upgrade at GitHub we monkey patched `Warning#warn` to be able to turn warnings into exceptions. However, there was no way to tell which warnings were deprecations and which were other types of warnings.

I want to expose the `category` on the `Warning` module so that I'm able to monkey patch `Warning#warn` and treat deprecation warnings differently from other warnings without using a regex the strings.

Here's an example program demonstrating what I'd like to get from Ruby by implementing this feature:

```ruby
module Warning
  def self.warn(msg, category: nil)
    if category == :deprecated
      raise msg 
    else
      super
    end 
  end 
end

def ivar
  Object.new.instance_variable_get(:@ivar)
end

# Doesn't raise, but warns with verbose set
ivar

# Raises an error
Object.new.tainted?
```

The PR I worked on with @tenderlove is here: https://github.com/ruby/ruby/pull/3418

It moves the `Warning` module to be written in Ruby, updates `rb_warning_s_warn` to pass kwargs, and adds a `category` to `Warning#warn`. 



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