psalm/docs/running_psalm/issues/PossiblyFalseArgument.md

PossiblyFalseArgument

Emitted when a function argument is possibly false, but the function doesn’t expect false. This is distinct from a function argument is possibly bool, which results in PossiblyInvalidArgument.

function foo(string $s) : void {
    $a_pos = strpos($s, "a");
    echo substr($s, $a_pos);
}