[BUG] "Method…should return Generator but returns false"

[mfn]

This is a false positive, because returning false from a method which yields still returns a Generator, see:

<?php

function foo(): Generator
{
    return false;
    yield "yolo";
}

var_dump(foo());

Output:

object(Generator)#1 (0) { }

See also https://3v4l.org/VcSpa

[ondrejmirtes]

I don't understand, what is a real-world usecase for this?

[tsufeki]

For example coroutines, see https://github.com/recoilphp/recoil/#returning-a-value-from-a-coroutine

[ondrejmirtes]

OK, my proposed fix is:

1. Turn off ReturnTypeRule for generator functions.
2. Get "custom node visitors" implemented - this is a feature that will allow efficient rules implementation for advanced stuff that depends on multiple nodes - for example, right now PHPStan does not complain about methods that should return something but do not contain return at all.
3. Write a special rule that will get executed only on generator functions and will look for an existing yield in the body.

[ondrejmirtes]

Implemented first part: 5b940d5

[muglug]

More examples: https://phpstan.org/r/da276b35474dead2cfa290e8d6b96ff1

function f() : Generator {
    yield 1;
    yield 2;
    return "hello";
}

function g() : Generator {
    if (rand(0, 1)) {
        return;
    }

    if (rand(0, 1)) {
        yield 1;
    }

    return "goodbye";
}

$f = f();
$g = g();

foreach ($f as $i) {
    var_dump($i);
}
var_dump($f->getReturn());

foreach ($g as $j) {
    var_dump($j);
}
var_dump($g->getReturn());

[muglug]

But the second option here should fail as in https://getpsalm.org/r/0ef6ef4478

function generator2() : Generator {
    if (rand(0,1)) {
        return;
    }
    yield 2;
}

function notagenerator() : Generator {
    if (rand(0,1)) {
        return;
    }
    return generator2();
}

[ondrejmirtes]

This already works, thanks.