Deprecate ActiveModel::Errors add_on_empty and add_on_blank methods

[morgoth]

Follow up to #18634 (comment)

[morgoth]

I'm not sure if we should delete this test https://github.com/rails/rails/pull/18996/files#diff-399b5cddc709ef96edf30de2328934deR56 as it doesn't have any equivalent in regular validations and :empty symbol is used only in deprecated add_on_empty method

[senny]

@morgoth let's remove that test when we remove the deprecated methods and keep it around for now.

[senny]

Even though we do not provide a direct replacement the deprecation message should give a hint where to look for similar behavior. It should be trivial to figure out what to change or where to look for more details.

[morgoth]

@senny I added tip to use PresenceValidator. In add_on_empty it's almost true ;-), as I'm not sure if we should describing implementation details here.

[senny]

The thing is that PresenceValidator is # :nodoc:. Don't think we should encourage it's use.

[morgoth]

What about "To achieve the same use validates_presence_of with :empty message"?

[senny]

If you have used add_on_empty its likely in a custom validation method with logic attached to it. That's probably why they didn't choose to use a validates_presence_of. Maybe combined with an :if option?

/cc @rafaelfranca

[rafaelfranca]

Yeah, it is more a kind of internal method to be used in custom validations. I think it is better to suggest people to write the actual code:

errors.add(attribute, :empty, options) if value.nil? || value.empty?

[morgoth]

@rafaelfranca I changed it to your suggestion

[rafaelfranca]

Same here but using blank?

[morgoth]

done

[senny]

@morgoth thank you 💛