[5.4] Reset format character added to date format validation

[arjasco]

This tiny addition should fix #17642

[ntzm]

Nice one, probably worth adding some tests to demonstrate the problem?

[themsaid]

@arjasco can you explain it more?

[arjasco]

If the ! is removed the added test will fail.

There is a problem in DateTime where when formatting by the month with no added day Y-m instead of Y-m-d it could overflow and give the incorrect month. Adding the ! will reset to the current and then parse the value, which in turn produces the correct date time.

In the PHP docs someone left a comment about 4 years ago describing the same thing.

See here: #17642, it should make sense then. So this most likely affects every version of Laravel because it's a PHP thing.

[taylorotwell]

Then just add it to your own date format when you pass it to the validator.

[arjasco]

@taylorotwell Appreciate this isn't the most elegant solution and most would probably question why a '!' is prepended in the source unless it's commented. However, adding this to your format won't work because the same format is being used for the comparison:

return $date && $date->format($parameters[0]) == $value;

Therefore when the format is performed if the '!' is there it will reset the date time and return false.

Check the issue thread again. (#17642) I posted about how now it's February the issue has disappeared. Problem is whenever we fall into a month that contains 31 days and we do validation against a month which doesn't have 31 days we get an incorrect result.

Understand this is such a tiny thing, just means you can't do this:

$this->validate(request(), [
    'date' => 'date_format:Y-m'
]);

Without having to change the format to 'Y-m-d' and doing a request merge to change the date input to append '-01' (adding the first day of the month is a work around as as long as you have d in your format)

Also doesn't seem like a widely known issue, so when it happens it's pretty confusing.