Add non-regression test for phpstan/phpstan#4846

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

tests/PHPStan/Rules/Variables/NullCoalesceRuleTest.php

@@ -377,6 +377,16 @@ public function testBug13921(): void
 		]);
 	}
 
+	public function testBug4846(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-4846.php'], [
+			[
+				'Property Bug4846\Foo::$alwaysString (string) on left side of ?? is not nullable.',
+				13,
+			],
+		]);
+	}
+
 	public function testBug14393(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-14393.php'], [

tests/PHPStan/Rules/Variables/data/bug-4846.php

@@ -0,0 +1,16 @@
+<?php declare(strict_types = 1);
+
+namespace Bug4846;
+
+class Foo
+{
+	public string $alwaysString = '';
+
+	public ?string $nullableString = null;
+}
+
+function (Foo $foo): void {
+	echo $foo->alwaysString ?? 'string';
+
+	echo $foo->nullableString ?? 'string';
+};