Support for endless loops

[herndlm]

Closes phpstan/phpstan#6807
Closes phpstan/phpstan#8463
Closes phpstan/phpstan#9374

analogue to while. contains also a slight simplification in the setting of $isAlwaysTerminating for while loops to keep this more in sync.

I had to switch the 2 test blocks in tests/PHPStan/Rules/Comparison/data/strict-comparison.php because the first one would be never exiting endless loop after this change, which would make the second one dead code and not testing anything useful any more.

[ondrejmirtes]

Please do not change anything about while. Change only for. After that is merged, you can send the while change as another PR and then we can think about it.

[herndlm]

Please do not change anything about while. Change only for. After that is merged, you can send the while change as another PR and then we can think about it.

It shouldn't change anything, just merges the elseif/else , so only refactor. But I might be overlooking something and can revert it again 😊

[herndlm]

adapted. the failing test cases seem to be OK, since in https://github.com/nikic/PHP-Parser/blob/v3.1.5/lib/PhpParser/ParserAbstract.php#L175-L344 there are 2 endless loops and the outer one does not seem to have a break statement. Replacing them with a while (true) makes it fail the same way.

[herndlm]

Saw this fixes some more issues, will add regression tests..
UPDATE: added, those were basically duplicates

[herndlm]

realized that I can make this better..

To do so I'd need #3578 first though :)

[phpstan-bot]

This pull request has been marked as ready for review.

[herndlm]

Thx to the pre-condition PR that was merged, I could make the endless loop detection more generic and better 🎉

Had to adapt a bit of test code in DefinedVariableRuleTest since it correctly figured out now that after those endless loops variables might not be defined.

I like the following one in particular where the conditions were switched and by mistake this resulted in an endless loop basically:

-for ($forI = 0; $forI < 10, $anotherVariableFromForCond = 1; $forI++, $forJ = $forI) {
+for ($forI = 0; $anotherVariableFromForCond = 1, $forI < 10; $forI++, $forJ = $forI) {

[ondrejmirtes]

Would something fail if you said $alwaysIterates = TrinaryLogic::createYes() here?

[herndlm]

no, apparently not. this comes basically from the other loops which have code like the following

$alwaysIterates = $condBooleanType->isTrue()->yes() && $context->isTopLevel();

but tbh, I didn't fully understand what the level here changes or does

[ondrejmirtes]

OK, makes sense to be consistent.

This condition asks about whether it's the "analysis iteration", or one of the "let's find out if types stabilize in the loop before we generalize them" that's done for all loops in a do-while like this:

phpstan-src/src/Analyser/NodeScopeResolver.php

Lines 1330 to 1360 in c3bb055

	do {
	$prevScope = $bodyScope;
	$bodyScope = $bodyScope->mergeWith($initScope);
	if ($lastCondExpr !== null) {
	$bodyScope = $this->processExprNode($stmt, $lastCondExpr, $bodyScope, static function (): void {
	}, ExpressionContext::createDeep())->getTruthyScope();
	}
	$bodyScopeResult = $this->processStmtNodes($stmt, $stmt->stmts, $bodyScope, static function (): void {
	}, $context->enterDeep())->filterOutLoopExitPoints();
	$bodyScope = $bodyScopeResult->getScope();
	foreach ($bodyScopeResult->getExitPointsByType(Continue_::class) as $continueExitPoint) {
	$bodyScope = $bodyScope->mergeWith($continueExitPoint->getScope());
	}
	foreach ($stmt->loop as $loopExpr) {
	$exprResult = $this->processExprNode($stmt, $loopExpr, $bodyScope, static function (): void {
	}, ExpressionContext::createTopLevel());
	$bodyScope = $exprResult->getScope();
	$hasYield = $hasYield || $exprResult->hasYield();
	$throwPoints = array_merge($throwPoints, $exprResult->getThrowPoints());
	$impurePoints = array_merge($impurePoints, $exprResult->getImpurePoints());
	}
	if ($bodyScope->equals($prevScope)) {
	break;
	}
	if ($count >= self::GENERALIZE_AFTER_ITERATION) {
	$bodyScope = $prevScope->generalizeWith($bodyScope);
	}
	$count++;
	} while ($count < self::LOOP_SCOPE_ITERATIONS);

[ondrejmirtes]

Thank you.