Add regression test for #14129

Closes phpstan/phpstan#14129

Author: phpstan-bot

tests/PHPStan/Analyser/nsrt/bug-14129.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace Bug14129;
+
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+
+	/**
+	 * @param array{foo: int}  $a
+	 */
+	public function doFoo(array $a): void
+	{
+		$k = rand(0, 1) ? 'a' : 'b';
+		$a[$k] = 256;
+		assertType('array{foo: int, a: 256}|array{foo: int, b: 256}', $a);
+	}
+
+	/**
+	 * @param array{foo: int}  $a
+	 * @param int<1,5> $intRange
+	 */
+	public function doBar(array $a, $intRange): void
+	{
+		$a[$intRange] = 256;
+		assertType('array{foo: int, 1: 256}|array{foo: int, 2: 256}|array{foo: int, 3: 256}|array{foo: int, 4: 256}|array{foo: int, 5: 256}', $a);
+	}
+
+}