PHP 8.4 support: switch implicit nullable types to explicit

[NickDickinsonWilde]

PHP 8.4 has deprecated implicit nullable types.. This will work as low as PHP 7.1 so no compatibility issues, but due to changed function signatures may necessitate a new major.

[bojanz]

As mentioned in the Drupal issue, breaking BC would require us to open a v3.0.0 branch, and I am not comfortable doing that for now, since v2 is still fairly new and hasn't achieved full adoption.

Users should turn off deprecation errors if these errors bother them.

I'll re-evaluate this decision at the end of 2025.

[ekes]

I don't see how this is a BC break. It's making explicit what is implicit. PHP is already interpreting it as ?type $v = NULL, when it is type $v = NULL.

To check I just run a test: Inheriting ?string with string https://3v4l.org/gas1U it's not complaining the signatures are different. In fact as this error shows https://3v4l.org/81TKa PHP (back to PHP7.1) actually interprets string $s = NULL as ?string $s = NULL.

Update from https://php.watch/versions/8.4/implicitly-marking-parameter-type-nullable-deprecated#change

On class methods, changing implicit nullable parameters to explicit parameters is not a backward-compatibility break.
Parent classes and child classes can replace the implicitly nullable parameter declarations with explicit declarations independently.

[bojanz]

I stand corrected, thank you @ekes. I just assumed PHP would complain.