Add regression test for #4525

Closes phpstan/phpstan#4525

Author: phpstan-bot

tests/PHPStan/Rules/Properties/TypesAssignedToPropertiesRuleTest.php

@@ -1009,4 +1009,9 @@ public function testBug12250(): void
 		$this->analyse([__DIR__ . '/data/bug-12250.php'], []);
 	}
 
+	public function testBug4525(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-4525.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Properties/data/bug-4525.php

@@ -0,0 +1,24 @@
+<?php // lint >= 7.4
+
+namespace Bug4525;
+
+use SplObjectStorage;
+
+class HelloWorld
+{
+	/**
+	 * @var SplObjectStorage<\DateTime, \DateTimeImmutable>
+	 */
+	private SplObjectStorage $map;
+
+	public function sayHello(): void
+	{
+		$this->map = new SplObjectStorage();
+	}
+
+	/** @phpstan-return SplObjectStorage<\DateTime, \DateTimeImmutable> */
+	public function getMap(): SplObjectStorage
+	{
+		return $this->map ??= new SplObjectStorage();
+	}
+}