Dependant types - parsing logic (can't think of a better subject - please change)

[pauljherring]

Bug report

As requested from #4694

Complicated logic not being recognised, leading to erroneous errors.

Code snippet that reproduces the problem

https://phpstan.org/r/3d974ed6-7d4b-4f91-8dcf-7187222d3004

<?php declare(strict_types = 1);
/**
* @return no-return
*/
function no_return(){
    echo "Dying\n";
    die(1);
}

/**
* @param int|null $u
* @param int|null $a
* @return array<int, int>
*/
function foo($u=null, $a=null){
    if (is_null($u) && is_null($a)){
        no_return();
	return [0,0]; // line 18
    }
    if ($u){
        $a = $u;
    }else if ($a){
        $u = $a;
    }
    return [$u, $a]; // line 25
}

print_r(foo(1)); // first only
print_r(foo(null,2)); // second only
print_r(foo(1,2)); // both
print_r(foo()); // none - will die() and not return

Actual output

18 | Unreachable statement - code above always terminates.
-- | --
25 | Function foo() should return array<int, int> but returns array<int, int|null>.

Expected output

18 | Unreachable statement - code above always terminates.

Line 18 added to check that no-return being honoured.

However $a (the int|null) will never be null if it gets that far through the function.

[pauljherring]

More complicated example (https://phpstan.org/r/b0b6a1f8-be8b-46a2-a936-c8b83dd960f7):

<?php declare(strict_types = 1);
/**
* @return no-return
*/
function no_return(){
    echo "Dying\n";
    die(1);
}

/**
* @param string $s
* @param int $x
* @return array<int>
*/
function x($s, $x){
	return [$s=>$x];
}
/**
* @param int|null $u
* @param int|null $a
* @return array{u:int, a:int}
*/
function foo($u=null, $a=null){
    $_u = null;
    $_a = null;
    if (is_null($u) && is_null($a)){
        no_return();
	return ['u'=>0,'a'=>0]; // line 28
    }
    if ($u){
	$_u = ['u'=>$u];
        $_a = x('a', $u);
    }else if ($a){
	$_a = ['a'=>$a];
        $_u = x('u', $a);
    }
    return ['u'=>$_u['u'], 'a'=>$_a['a']]; // line 37
}

$x = foo(1);
echo $x['a'];
echo $x['u'];

Output

28 | Unreachable statement - code above always terminates.
-- | --
37 | Offset 'a' does not exist on array<int>\|null.
37 | Offset 'u' does not exist on array<int>\|null.

Expected

28 | Unreachable statement - code above always terminates.

[ondrejmirtes]

I offer two alternatives that are already understood by the static analyser as of dev-master:

• https://phpstan.org/r/5621d3c1-ad7f-41fc-886f-54b9a2e3c0c6
• https://phpstan.org/r/5359cc00-aaaa-44a4-8ce6-70d72b2cccab

[github-actions]

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