Add regression test for #10749

Closes phpstan/phpstan#10749

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ondrejmirtes

tests/PHPStan/Rules/Properties/TypesAssignedToPropertiesRuleTest.php

@@ -1066,4 +1066,9 @@ public function testBug10924(): void
 		$this->analyse([__DIR__ . '/../Methods/data/bug-10924.php'], []);
 	}
 
+	public function testBug10749(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-10749.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Properties/data/bug-10749.php

@@ -0,0 +1,27 @@
+<?php declare(strict_types = 1);
+
+namespace Bug10749;
+
+use ArrayAccess;
+
+/**
+ * @template T of array<string, mixed>
+ * @implements ArrayAccess<key-of<T>, value-of<T>>
+ */
+abstract class Base implements ArrayAccess
+{
+
+	/** @var T */
+	protected array $data = [];
+
+	/**
+	 * @template K of key-of<T>
+	 * @param K|null $offset
+	 * @param T[K] $value
+	 */
+	public function offsetSet($offset, $value): void
+	{
+		$this->data[$offset] = $value;
+	}
+
+}