Add regression test for #7978

Closes phpstan/phpstan#7978

Author: phpstan-bot

tests/PHPStan/Analyser/nsrt/bug-7978.php

@@ -0,0 +1,24 @@
+<?php declare(strict_types = 1);
+
+namespace Bug7978;
+
+use function PHPStan\Testing\assertType;
+
+class Test {
+
+	const FIELD_SETS = [
+		'basic'   => ['username', 'password'],
+		'headers' => ['app_id', 'app_key'],
+	];
+
+	public function doSomething(): void
+	{
+		foreach (self::FIELD_SETS as $type => $fields) {
+			$credentials = [];
+			foreach ($fields as $field) {
+				$credentials[$field] = 'fake';
+			}
+			assertType("array{app_id?: 'fake', app_key?: 'fake', password?: 'fake', username?: 'fake'}", $credentials);
+		}
+	}
+}