Fix false positive UnhandledMatchError throw point

[rajyan]

closes phpstan/phpstan#6910

match ($this->heldFish instanceof RedFish) {
	true => 'hello',
	false => 'world', // $this->heldFish instanceof RedFish === false is always true here
       // $this->heldFish is *NEVER* here but $this->heldFish instanceof RedFish is not
};

the logic in NodeScopeResolver is only checking whether the remaining type is never and cannot understand that UnhandledMatchError is not thrown.

Noticed that most false positive cases like in the tests can be solved by adding a similar logic to

phpstan-src/src/Rules/Comparison/MatchExpressionRule.php

Lines 63 to 82 in 2b9d212

	$armLine = $armCondition->getLine();
	if (!$armConditionResult->getValue()) {
	$errors[] = RuleErrorBuilder::message(sprintf(
	'Match arm comparison between %s and %s is always false.',
	$armConditionScope->getType($matchCondition)->describe(VerbosityLevel::value()),
	$armConditionScope->getType($armCondition->getCondition())->describe(VerbosityLevel::value()),
	))->line($armLine)->build();
	} else {
	$nextArmIsDead = true;
	if (
	$this->checkAlwaysTrueStrictComparison
	&& ($i !== $armsCount - 1 || $i === 0)
	) {
	$errors[] = RuleErrorBuilder::message(sprintf(
	'Match arm comparison between %s and %s is always true.',
	$armConditionScope->getType($matchCondition)->describe(VerbosityLevel::value()),
	$armConditionScope->getType($armCondition->getCondition())->describe(VerbosityLevel::value()),
	))->line($armLine)->build();
	}
	}

If there is a always true condition, UnhandledMatchError is not thrown.

[ondrejmirtes]

Thank you! I changed the base to 1.5.x.