Here is a code snippet that shows a misleading error when intval() is used with a non-scalar.

<?php

class Foo
{
    private int $x = 0;
    
    function __construct() {
        $this->x += intval(new stdClass());
    }
}

8      Property Foo::$x (int) does not accept (float|int).  

It's reproducible with checkBenevolentUnionTypes: true

I've traced the issue.

intval() with non-scalar argument resolves to ErrorType which is inherited from MixedType.

So ErrorType::toNumber() returns UnionType of int and float. When above math expression is resolved it has int on the left side and float|int on the right side which produces error when checkBenevolentUnionTypes is on.

The root cause is fixed in this PR. It adds non-scalar value handling by making sure that return type for intval/floatval in all cases is int i.e. float.

PHP is throwing a warning on use of non-scalar with intval/floatval and not an error like with strval, so even though non-scalar arguments shouldn't be used we should handle them.