Added regression test (#5585)

Author: staabm

tests/PHPStan/Analyser/nsrt/bug-9004.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace Bug9004;
+
+use function PHPStan\Testing\assertType;
+
+$test = [];
+foreach (['a', 'b', 'c'] as $letter) {
+	if (rand(0, 1) == 0) {
+		assertType("array{}|array{hi: 'hello'}|array{hi: array{0: 42, 1?: 42}}", $test);
+		if (isset($test['hi']) && is_string($test['hi'])) {
+			continue;
+		}
+		$test['hi'][] = 42;
+	} else {
+		$test['hi'] = 'hello';
+	}
+}

tests/PHPStan/Rules/Arrays/OffsetAccessAssignmentRuleTest.php

@@ -222,4 +222,15 @@ public function testAppendToArrayWithPhpIntMaxKey(): void
 		]);
 	}
 
+	public function testBug9004(): void
+	{
+		$this->checkUnionTypes = true;
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-9004.php'], [
+			[
+				'Cannot assign new offset to list<int>|string.',
+				14,
+			],
+		]);
+	}
+
 }