Added regression test

Author: staabm

tests/PHPStan/Analyser/nsrt/bug-13385b.php

@@ -0,0 +1,51 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13385b;
+
+use function PHPStan\Testing\assertType;
+
+interface Operator {
+	public function priority(): int;
+	public function calculate(int $a, int $b): int;
+}
+
+class HelloWorld
+{
+	/**
+	 * @param list<Operator|int> $children
+	 */
+	public function calculate(array $children): int {
+		$operands  = [];
+		$operators = [];
+
+		foreach ($children as $child) {
+			if ($child instanceof Operator) {
+				while ($operators !== []) {
+					$op    = array_pop($operators);
+					$left  = array_pop($operands) ?? 0;
+					$right = array_pop($operands) ?? 0;
+
+					assert(is_int($left));
+					assert(is_int($right));
+
+					$value = $op->calculate($left, $right);
+
+					assertType(Operator::class, $op);
+					assertType('int', $left);
+					assertType('int', $right);
+					assertType('int', $value);
+
+					$operands[] = $value;
+
+					assertType('non-empty-list<int>', $operands);
+				}
+
+				$operators[] = $child;
+			} else {
+				$operands[] = $child;
+			}
+		}
+
+		return count($operands) === 1 ? reset($operands) : 0;
+	}
+}