Feature: Exclude and Conditional Rules

[JasonTheAdams]

This PR adds the following rules:

• Exclude
• ExcludeIf
• ExcludeUnless
• OptionalIf
• OptionalUnless
• NullableIf
• NullableUnless

The Exclude rules will prevent any further validation rules from applying to the value, and then exclude the value entirely from the Validator::validated() returned data. This is useful for preventing a complex set of rules from occurring while communicating that the value should not be considered validated.

Next, the If and Unless suffixed rules allow apply the rules only if or unless the dataset conditions apply. For example:

$validator = new Validator([
  'attending_event' => ['required']
  't_shirt_size' => ['excludeUnless:attending_event,yes']
], $values);

In this case, the t_shirt_size is only included in the validated values if the user said they're attending the event. The same conditional thinking applies to the Optional and Nullable counterparts, while maintaining their distinct rules.

[JasonTheAdams]

@jonwaldstein I would appreciate a review on this so I can use it in Next Gen.

[bordoni]

Small set of questions and a docblock.

[bordoni]

I wonder if we should allow allow conditions to be overwritten directly on an existing Rule by moving this to a method and calling it here on construct.

[JasonTheAdams]

Unless you have a clear and immediate case in mind, I'm inclined to keep this simple until a use case arrises.

[bordoni]

Do we want to use new static() in case we want to be able to extend Exclude?

[JasonTheAdams]

I've become very reluctant to use new static() prematurely, as it's bitten me in the past. It's not obvious, but when using new static() one is locking in the constructor for child classes, so to pass static analysis one must use an interface or make __construct() final. Either way, you end up limiting inheritance. So until a use case comes up, I've found it's better to assume child classes will override this method if need be, allowing them to also change the constructor.

[jonwaldstein]

Is there a reason we are checking for an empty string or null or can we just do empty($value)?

[JasonTheAdams]

Because empty(0) equals true, and in this case that can be a valid value which shouldn't prevent further validation.

[jonwaldstein]

What about if the value was an empty array?

[JasonTheAdams]

I would think that should still go through validation. It doesn't now, but I could conceive of the min/max (or minLength/maxLength) rules still being useful here: 'repeater' => ['min:0', 'max:3']

In any case, we're not really handling arrays, yet. So I'd rather add that later once we've thought through it more and have a need.

[JasonTheAdams]

Thank you for your reviews, @bordoni and @jonwaldstein! I've addressed your obvious fixes and replied for conversation to other comments. Back to you for review or response. 🙂

[jonwaldstein]

@JasonTheAdams nice job! i'm interested in seeing these rules in action. 🥋