callable(&int) should not be a subtype of callable(int)

[AndrolGenhald]

Closure could still take its argument by reference though, and again mutate it. https://psalm.dev/r/3423b8e3e9

Originally posted by @someniatko in #8212 (comment)

@someniatko huh, you're right. I'd consider that a separate bug though. I think we need to add annotation for references in callables and make callable(&int) not be a subtype of callable(int), because the example I just gave crashes...

Originally posted by @AndrolGenhald in #8212 (comment)

I don't believe we even have a way to annotate callables that take arguments by ref right now, so this is probably going to take a bit of work.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/3423b8e3e9

<?php

/**
 * @psalm-template-covariant T of string|int|float
 * @psalm-immutable
 */
final class ValueReference {
    /**
     * @param T $value
     */
    public function __construct(
        public readonly mixed $value
    ) {}

    /**
     * @template Tu of string|int|float
     *
     * @param (Closure(T): Tu) $f
     *
     * @return ValueReference<Tu>
     */
    public function map(Closure $f): ValueReference
    {
        $new = $f($this->value);

        return new ValueReference($new);
    }
}

$a = new ValueReference('hello');
$b = $a->map(/** @param-out string $val */ function(string &$val) { $val = $val . ' world'; return $val; });

print $b->value; // hello world

Psalm output (using commit 85fe7e8):

ERROR: ImpureFunctionCall - 24:16 - Cannot call an impure function from a mutation-free context

https://psalm.dev/r/e59d68ba57

<?php

/** @param callable(int): int $closure */
function takesClosure($closure): int
{
    return $closure(123);
}

function takesIntByRef(int &$i): int
{
    return $i**2;
}

takesClosure("takesIntByRef");

Psalm output (using commit 85fe7e8):

No issues!