UnusedFunctionCall reported when using unserialize or serialize

[VincentLanglet]

serialize and unserialize can throw exceptions.

I got the issue with a unit test

public function testCannotSerialize(): void
    {
        $this->expectException(BadMethodCallException::class);
        serialize(new Foo());
    }

but it can be reproduce this way https://psalm.dev/r/c501b39d6d
so psalm shouldn't report an error.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/c501b39d6d

<?php

class Foo
{
    public function __sleep(): array
    {
        throw new BadMethodCallException(sprintf('Cannot serialize %s.', self::class));
    }
    public function __wakeup(): void
    {
        throw new BadMethodCallException(sprintf('Cannot unserialize %s.', self::class));
    }
}

function test(): bool {
    try {
        serialize(new Foo());
    } catch (\Throwable) {
        return false;
    }
    
    return true;
}

Psalm output (using commit 7c83878):

ERROR: UnusedFunctionCall - 17:9 - The call to serialize is not used

[orklah]

serialize is considered pure. This is very questionnable, as serialize will possibly call a bunch of code that can't be determined.

Given it's pure and we don't have a specific stub that documents the function can throw, we consider it useless.

So 2 ways to fix: changing serialize to impure here:

psalm/src/Psalm/Internal/Codebase/Functions.php

Line 406 in 2ef9939

$impure_functions = [

or adding a stubs in CoreGenericFunctions to document the throw

[VincentLanglet]

I tried #8650 @orklah.
The idea was to still mark serialize as pure if we're not passing an object, because I have a psalm error with the code base (see first commit).