added regression test

Author: staabm

tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php

@@ -1270,4 +1270,10 @@ public function testDeepDimFetch(): void
 		$this->analyse([__DIR__ . '/data/deep-dim-fetch.php'], []);
 	}
 
+	#[RequiresPhp('>= 8.0')]
+	public function testBug9494(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-9494.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Methods/data/bug-9494.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace Bug9494;
+
+class Fib
+{
+	/** @var array<int, ?int> 0-indexed memoization */
+	protected $mem = [];
+
+	public function __construct(public int $limit) {
+		$this->mem = array_fill(2, $limit, null);
+	}
+
+	/**
+	 * Calculate fib, 1-indexed
+	 */
+	public function fib(int $n): int
+	{
+		if ($n < 1 || $n > $this->limit) {
+			throw new \RangeException();
+		}
+
+		if ($n == 1 || $n == 2) {
+			return 1;
+		}
+
+		if (is_null($this->mem[$n - 1])) {
+			$this->mem[$n - 1] = $this->fib($n - 1) + $this->fib($n - 2);
+		}
+
+		return $this->mem[$n - 1];  // Is always an int at this stage
+	}
+
+	/**
+	 * Calculate fib, 0-indexed
+	 */
+	public function fib0(int $n0): int
+	{
+		if ($n0 < 0 || $n0 >= $this->limit) {
+			throw new \RangeException();
+		}
+
+		if ($n0 == 0 || $n0 == 1) {
+			return 1;
+		}
+
+		if (is_null($this->mem[$n0])) {
+			$this->mem[$n0] = $this->fib0($n0 - 1) + $this->fib0($n0 - 2);
+		}
+
+		return $this->mem[$n0];
+	}
+}