Based on a discussion under a commit that converts $this->assert*() to self::assert*() in Doctrine: doctrine/dbal@62eb475#commitcomment-24420550

PHP still allows calling static method non-statically, although such behavior could be considered unsafe and not a good practice. Hopefully PHP will come to a point where this behavior will be deprecated.

Example:

class Test
{
	public function foo() : void
	{
		$this->bar();
	}
	
	public static function bar() : void
	{
	}
}

This currently works, PHP has no problems with mixing static and non-static calls (sadly). Also PHPStan is happy.

I'd like to propose a new rule that would ban this abomination altogether. 🥇 I'd love to see it in core in L5/L6 for example, but if it's too agressive (some people may think so), at least to be included in the upcoming phpstan-extra-strict-rules repo.

Thoughts?

cc-ing @PowerKiKi & @Ocramius from the abovementioned discussion.