Added regression test

Author: staabm

tests/PHPStan/Rules/Arrays/DeadForeachRuleTest.php

@@ -50,4 +50,9 @@ public function testBug2560(): void
 		$this->analyse([__DIR__ . '/data/bug-2560.php'], []);
 	}
 
+	public function testBug2457(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-2457.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Arrays/data/bug-2457.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Bug2457;
+
+class HelloWorld
+{
+	public function sayHello(array $x, array $y): void
+	{
+		$a = [];
+		$o = [];
+
+		foreach ($x as $t) {
+			if (!isset($a[$t])) {
+				$a[$t] = [];
+			}
+			$o[] = 'x';
+			array_unshift($a[$t], count($o) - 1);
+		}
+
+		foreach ($y as $t) {
+			if (!isset($a[$t])) {
+				continue;
+			}
+			foreach ($a[$t] as $b) {
+				// this will be reached
+			}
+		}
+	}
+}