Prevent inheritance of class template types in static methods

[muglug]

Instance template parameters should not be made available to static methods – this was a flaw in my implementation, now fixed. If/when generics are available at the language level this can be re-evaluated.

/**
 * @template T
 */
class C {
    /**
     * @param T $t
     */
    public static function foo($t) : void {}
}

https://phpstan.org/r/e00cd9e1-3aba-4e6c-ab9a-8e63da122b94

Expected: some sort of error (in Psalm for now it just treats it as a missing docblock class, you may want something more helpful).

[ondrejmirtes]

So I've stumbled upon this interesting example: https://phpstan.org/r/81f2efd0-b769-4685-a5aa-a8f914fda95a

And it seems to work in Psalm too, although it's about class-level T that's used above a static method which contradicts this feature request. What do you think is the difference @muglug?

[muglug]

Yeah, I decided against this in the end (hence why the example now works in Psalm) because penalising a legitimate usage was unfair

[ondrejmirtes]

@muglug So what's the difference that this one still marks T as unknown? https://psalm.dev/r/c93629faa3

[dktapps]

Maybe a better option is to allow this, but report static usages where the type can't be inferred (e.g. Class::thing() can't be inferred but $someObject::thing() should be able to).
For example: https://phpstan.org/r/acf73820-4728-426f-9d38-7d479eb22af0

[vhenzl]

I have just run into this problem.

Let's assume code like this (a simplified version of this Maybe type implementation):

/**
 * @template T
 */
final class Maybe
{
    private function __construct(
        /** @var T */
        public mixed $value = null,
    ) {
    }

    /**
     * @param T $value
     * @return Maybe<T>
     */
    public static function just(mixed $value): self
    {
        return new self($value);
    }
}

And example use:

$ms = Maybe::just('abc');
$mi = Maybe::just(123);

The code of Maybe class is wrong, the static method just() shouldn't use T template but define its own @template V, accept parameter V $value and return Maybe<V>.

Because PHPStan didn't complain about "unknown type T" (or whatever the error message should be), I assumed that the code is correct and that the inferred type of $ms and $mi is Maybe<string> and Maybe<int> respectively.

To my surprise, I later found out that for PHPStan the return type of just() is always Maybe<mixed>. And since the type is mixed, PHPStan allows any operation with the value, hiding errors further down in the code.

This is rather dangerous behaviour because PHPStan doesn't complain about anything and gives a false feeling that everything works correctly.

[phpstan-bot]

@ondrejmirtes After the latest push in 2.0.x, PHPStan now reports different result with your code snippet:

@@ @@
+28: Expression "$car === 'aaa'" on a separate line does not do anything.
 28: Strict comparison using === between Car and 'aaa' will always evaluate to false.

Full report

Line	Error
28	Expression "$car === 'aaa'" on a separate line does not do anything.
28	Strict comparison using === between Car and 'aaa' will always evaluate to false.