`missing_presence_validation` incorrectly marks `numericaility` with `allow_nil: false` as missing a presence validator

[vanharen]

first off, thanks for the gem! very handy!

so, to be honest, i'm not 100% convinced this is really a bug, but figured i'd raise it, just in case it is. please excuse me if this has been discussed previously -- i was unable to find any mention of it in issues.

so -- if you have a non-null integer field that has a validation like:

  validates :rank, numericality: {greater_than_or_equal_to: 0}, allow_nil: false

then it is my belief that this should suffice as a presence validator even though presence: true is not explicitly listed in the validator. one could include this but it is redundant, imho, based on the following (from https://guides.rubyonrails.org/active_record_validations.html#numericality)

By default, numericality doesn't allow nil values. You can use allow_nil: true option to permit it. For Integer and Float columns empty strings are converted to nil.

so in the example above allow_nil: false should not really even be necessary as it is the default. so the existence of the numericality: validator -- in the absence of allow_nil: true should suffice to be a presence validator for non-null integer columns, yes?

if my assertion is correct, i'd consider adding a PR to address this, once i get my fingers into the code. i welcome discussion. thanks for reading!

[fatkodima]

yes, looks reasonable to me. Please do open a PR.

[gregnavis]

@vanharen, thank you for your comment. Discussion is always much appreciated!

I don't think treating allow_nil: false (which is the default as you mentioned) is a good idea. Technically, it does report a validation error, but we want to help application developers deliver the best possible user experience.

In this case, if you leave rank empty you'll get an error of type :not_a_number with a message "Rank is not a number". I think this is a very confusing error from a user's perspective, especially that it'll additionally be shown when the field contains an invalid value.

If you do:

validates :rank, presence: true
validates :rank, numericality: { greater_than_or_equal_to: 0 }

then leaving rank blank will result in two messages ("Rank is blank", "Rank is not a number"), which is confusing. In this case, better UX can be achieved by adding allow_nil to numericality validator (and I'm working on a detector to do just that).