Rules returning nil

[inkstak]

Hi @palkan

The following issue may be about a bug or about good practice.

Reproduction Script: https://gist.github.com/inkstak/448b44bbe97582c26dda00ff043ada4d

  def manage?
    if condition_a?
      perform_complicated_check
    elsif condition_b?
      perform_another_complicated_check
    end
  end

When none of the conditions match, the rule above will return nil.
It's working fine when calling authorize! or allowed_to?.

However, it fails using the RSpec DSL

  describe_rule :manage? do
    failed "without any conditions"
  end

  1) UserPolicy manage? without any conditions is denied
     Failure/Error: failed "without any conditions"
     
       Expected to fail but succeed:
       <UserPolicy#manage?: >

I thought it was a common practice to accept a predicate method to return nil,
but the failed method is always expecting false.

The workaround is dead simple : always return false at least by adding an else false to the rule.

But should I add that just to please the specs?
Or should we state that a rule must always return true or false?

[palkan]

should I add that just to please the specs?

I would say it's not about specs but about the API consistency; predicates must return true or false, there should be no third boolean value.

Thus, it's the latter:

should we state that a rule must always return true or false?