How to declare relation between properties (enum and nullable field)

[mhsdesign]

Say i have an enum and a nullable property. How can i tell phpstan to expect the nullable property to be not null depending on the value of the enum?

<?php declare(strict_types = 1);

enum Type
{
    case FOO_IS_NULL;
    case FOO_IS_STRING;
}

final readonly class FooHolder
{
    private function __construct(
        public Type $type,
        public ?string $foo
    ) {
        if ($this->type === Type::FOO_IS_STRING && $this->foo === null) {
             throw new \InvalidArgumentException('The foo must be set if the type is string.', 1695118377);
         }
    }

    public static function createEmpty(): self
    {
        return new self(Type::FOO_IS_NULL, null);
    }

    public static function createFromString(string $value): self
    {
        return new self(Type::FOO_IS_STRING, $value);
    }
}


$foo1 = FooHolder::createFromString('hi');
assert($foo1->type === Type::FOO_IS_STRING);
assert(is_string($foo1->foo));

$foo2 = FooHolder::createEmpty();

function fooMe(FooHolder $afoo): void
{
    if ($afoo->type === Type::FOO_IS_NULL) {
        // how to teach phpstan this relation? Foo should be null. And this should not raise an Error.
        // assert($afoo->foo === null);
		someFunctionThatOnlyAcceptsNull($afoo->foo);
    }
    if ($afoo->type === Type::FOO_IS_STRING) {
        // how to teach phpstan this relation? Foo should be string. And this should not raise an Error.
        // assert(is_string($afoo->foo));
		someFunctionThatOnlyAcceptsString($afoo->foo);
    }
}

function someFunctionThatOnlyAcceptsNull(null $variable): void {}
function someFunctionThatOnlyAcceptsString(string $variable): void {}
	
fooMe($foo1);
fooMe($foo2);

I know that for methods one can leverage @phpstan-assert-if-true.
I thought that this problem would be solvable via generics but i didnt found the solution on my own ^^

A real world usecase can be found here: The NodeName must be set if the Node's classification is tethered.
https://github.com/neos/neos-development-collection/blob/b7cde7481ba42d3f7a76949c84d7dfc8b7fdd27c/Neos.ContentRepository.Core/Classes/Projection/ContentGraph/Node.php#L56-L60

What do you say? :D

[ondrejmirtes]

Please reproduce this on phpstan.org/try and tell us what the expected output is as opposed to the actual PHPStan output.

[mhsdesign]

Hi @ondrejmirtes. I was not suggesting that there is anything wrong with phpstan, but its probably just my lack of creativity to annotate that to phpstan, or the usecase might not be supported yet.

I copied the example over to phpstan/try: https://phpstan.org/r/eaf626df-9a19-40fc-a721-f9ccb57325b8
And in my imagination i would like to annotate $something in the class so that phpstan fully understand the code without any asserts on the calling site.

And i wondered if this is somehow depictable with generics?

[ondrejmirtes]

No you can't express this with the current type system.

If I were you I'd choose a different object design. Usage of nullable or optional parameters is usually a code smell. You should have separate EmptyHolder and StringHolder classes.

[mhsdesign]

yes sure that option exists. In my real live example this was not doable with a reasonable amount of effort and not desired ^^

Do you think it would be useful to have this as a feature similar to@phpstan-assert-if?

/** @phpstan-assert-if-true !null $this->getName() */
public function hasName(): bool
{
    return $this->name !== null;
}

public function getName(): ?string
{
    return $this->name;
}

Maybe i can look into it.

[ondrejmirtes]

There is already a feature request #10463

[mhsdesign]

Okay well in that case i think we can close this discussion ;) Thanks for your input ❤️