Feature: Opaque Validator

[DmitryBochkarev]

In some situations, simple error messages are uninformative and can sometimes lead to data leaks. And it would be nice to give another message instead.

An example of a leak and unnecessary noise

IncludedIn = Struct.new(:value) do
  def included_in?(collection)
  	collection.include?(value)
  end

  def inspect
    value.inspect
  end
end

existing_projects =
  FlexValidations::And.new(
	positive_integer,
	FlexValidations::Chain.new(
      FlexValidations::Decorate.new(IncludedIn),
	  FlexValidations::Predicate.new(:included_in?, Project.all.map(&:id))
    )
  )

puts existing_projects.validate(3)

# chain of validation for 3 failed:
#   1. decorated 3 now 3;
#   2. 3.included_in?([1, 2]) failed.

As I can see it should be:

existing_projects =
  FlexValidations::Opaque.new(
	  FlexValidations::And.new(
		positive_integer,
		FlexValidations::Chain.new(
	      FlexValidations::Decorate.new(IncludedIn),
		  FlexValidations::Predicate.new(:overlap?, Project.all.map(&:id))
	    )
	  ),
	  fail: "Invalid project"
  )

puts existing_projects.validate(3)

# Invalid project