Bug report

This one has me stumped after trying many different variants of the PHPDoc tags on throwOnFailure(). As best I can tell, PHPStan is widening the incoming type from <something>|false to <something>|bool, which it then narrows to <something>|true per the conditional return type.

<?php declare(strict_types=1);

class A
{
    private int $Counter = 0;

    /**
     * @return stdClass
     */
    public function getMayFail()
    {
		// PHPStan reports "Method A::getMayFail() should return stdClass but returns stdClass|true."
        return $this->throwOnFailure($this->mayFail());
    }

    /**
     * @template T
     *
     * @param T $result
     * @return (T is false ? never : T)
     */
    public function throwOnFailure($result)
    {
        if ($result === false) {
            throw new Exception('Operation failed');
        }
        return $result;
    }

    /**
     * @return stdClass|false
     */
    public function mayFail()
    {
        $this->Counter++;
        return $this->Counter % 2 ? new stdClass() : false;
    }
}

If I change the DocBlock to this, it works:

    /**
     * @template T
     *
     * @param T|false $result
     * @return ($result is false ? never : T)
     */

...but other tools (Intelephense, at least) don't like it and it isn't amenable to adding a second template for the failure value (e.g. so the caller can specify whether false or -1 are regarded as failures); and the original syntax should work 😉

Code snippet that reproduces the problem

https://phpstan.org/r/06424f05-e1f9-4d72-903b-0f2cc1cc183b

Expected output

No errors; types should narrow to exclude false without adding true.

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