Fails to infer return type for method using static callable

[leflings]

https://psalm.dev/r/2791d5c034

I would expect return type of combineAll1 to be inferable from the context.

Oddly enough, psalm has no issue with the "callable"-form used in combineAll2. (I wonder if this is because Psalm just "gives up" with this form or if it actually understands it?)

I prefer (and believe is php standard?) to supply the callable in the first form [class, method] as this is understood by PhpStorm when finding usages and navigating to implementation.

Possible duplicate of #5388 though from my (mostly inexperienced) perspective they seem to be two slightly different cases.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/2791d5c034

<?php

declare(strict_types=1);

final class DaysInterval
{
    private ?int $min;

    private ?int $max;

    public function __construct(?int $min, ?int $max)
    {
        $this->min = $min;
        $this->max = $max;
    }

    public function getMin(): ?int
    {
        return $this->min;
    }

    public function getMax(): ?int
    {
        return $this->max;
    }

    public static function combineAll1(self ...$intervals): self
    {
        return array_reduce($intervals, [self::class, 'combine'], new self(0, 0));
    }
    
    public static function combineAll2(self ...$intervals): self
    {
        return array_reduce($intervals, self::class . '::combine', new self(0, 0));
    }

    public static function combine(self $a, self $b): self
    {
        $newMin = max($a->getMin() ?? \PHP_INT_MAX, $b->getMin() ?? \PHP_INT_MAX);
        $newMax = max($a->getMax() ?? \PHP_INT_MAX, $b->getMax() ?? \PHP_INT_MAX);

        if ($newMin > $newMax) {
            $newMin = $newMax;
        }

        if ($newMin === \PHP_INT_MAX) {
            $newMin = null;
        }
        if ($newMax === \PHP_INT_MAX) {
            $newMax = null;
        }

        return new self($newMin, $newMax);
    }
}

Psalm output (using commit 8c13752):

INFO: MixedReturnStatement - 29:16 - Could not infer a return type

INFO: MixedInferredReturnType - 27:61 - Could not verify return type 'DaysInterval' for DaysInterval::combineAll1

[weirdan]

Simplified a bit: https://psalm.dev/r/4d5778d2aa

I wonder if this is because Psalm just "gives up" with this form or if it actually understands it?

Psalm understands that, see the trace produced by the linked snippet.

Possible duplicate of #5388 though from my (mostly inexperienced) perspective they seem to be two slightly different cases.

They are likely separate, because Psalm has custom code to infer array_reduce return type.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/4d5778d2aa

<?php

final class DaysInterval {
    public function __construct() {}

    public static function combineAll1(self ...$intervals): self {
        return array_reduce($intervals, [self::class, 'combine'], new self());
    }
    
    public static function combineAll2(self ...$intervals): self {
        $ret = array_reduce($intervals, self::class . '::combine', new self());
        /** @psalm-trace $ret */;
        return $ret;
    }

    public static function combine(self $_a, self $_b): self {
        return new self();
    }
}

Psalm output (using commit 9e9413d):

INFO: MixedReturnStatement - 7:16 - Could not infer a return type

INFO: MixedInferredReturnType - 6:61 - Could not verify return type 'DaysInterval' for DaysInterval::combineAll1

INFO: Trace - 12:33 - $ret: DaysInterval