Cannot detect check for null when assigning to a variable

[Nyholm]

I found this bug. Not sure if it is "too complex" or not. I just thought to report it.

function takesAString(string $name): void {
    echo "hello: ".$name;
}

function randomReturn(): ?string {
    return rand(1,2) === 1 ? 'foo' : null;
}

$name = randomReturn();

// Assignment in if does not work
if ($hasStringValue = $name !== null) {
    takesAString($name);
}

https://psalm.dev/r/c9ebe1f843

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/c9ebe1f843

<?php

function takesAString(string $name): void {
    echo "hello: ".$name;
}

function randomReturn(): ?string {
    return rand(1,2) === 1 ? 'foo' : null;
}

$name = randomReturn();

// This comparison works file
if ($name !== null) {
    takesAString($name);
}

// Adding comparison to variable does not work
$hasStringValue = $name !== null;
if ($hasStringValue) {
    takesAString($name);
}


// Assignment in if does not work
if ($hasStringValue = $name !== null) {
    takesAString($name);
}

Psalm output (using commit 29eb830):

ERROR: PossiblyNullArgument - 21:18 - Argument 1 of takesAString cannot be null, possibly null value provided

ERROR: PossiblyNullArgument - 27:18 - Argument 1 of takesAString cannot be null, possibly null value provided

INFO: UnusedVariable - 26:5 - Variable $hasStringValue is never referenced

[muglug]

Generally if it works in TypeScript it should work in Psalm, and the example in this ticket works in TypeScript (so it now works in Psalm too).

The other example in the link doesn't work in Psalm, as it would require some pretty complex analysis:

$hasStringValue = $name !== null;
if ($hasStringValue) {
    takesAString($name);
}

[Nyholm]

Lovely. Thank you for a quick fix.

[muglug]

The fix caused a regression so I'm unfixing for now