I never know whether its $context->truthy() or $context->true().

please add a test with a === true comparison
(the escaped mutant at least tells us, its not covered by tests)

I added a test for the === true comparison, but for a function returning bool it does not distinguish between $context->true() and $context->truthy(): both lead to the same narrowing on the true branch. So the test covers the syntax, but it does not really prove which context check is the correct one here.

does this test really depend on php 8.4? I think this can be lowered without problems?

I understand that array_all is a function added in PHP 8.4. Therefore, the tests are set for 8.4 and later.
I ran it on my machine and it passed on 8.3 (I'm not sure why this is), so should I remove the mention of 8.4 and later?

good point. it works on 8.3 because we have symfony/polyfills.

leave it as is than, thanks.

I don't think this is the right approach, but don't have a better idea atm either

I initially considered performing type specification for arbitrary closures, but I concluded that this would require tracking the result of executing statements, which does not seem realistic. I also do not think that would align well with PHPStan’s design.

For that reason, I implemented it so that type specification is applied only to closures that contain nothing but a return statement.

Another option would be to apply type specification only to closures produced by converting a function to a first-class callable. I considered this because assertions written in PHPDoc can exist on the original function. However, at the time of implementation, that assertion information was lost when the function was converted to a closure, so this did not seem realistic either.

(The issue I opened about that, phpstan/phpstan#14249, has since been resolved, so this may become a viable option in the future. However, at least for now, I also cannot think of a better alternative, so I think this approach is acceptable as a temporary solution.)

I agree with @staabm that this might not be satisfying.

The first thing I thought then was to check how it was done for array_filter (in ArrayFilterFunctionReturnTypeHelper) and they seems to do something similar

if ($callbackArg instanceof Closure && count($callbackArg->stmts) === 1 && count($callbackArg->params) > 0) {
			$statement = $callbackArg->stmts[0];
			if ($statement instanceof Return_ && $statement->expr !== null) {

But it handles also

 elseif (
			($callbackArg instanceof FuncCall || $callbackArg instanceof MethodCall || $callbackArg instanceof StaticCall)
			&& $callbackArg->isFirstClassCallable()
		)

and

else {
			$constantStrings = $scope->getType($callbackArg)->getConstantStrings();
			if (count($constantStrings) > 0) {

So I think we could have more case to handle.