test: add test for offset access legal

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -776,6 +776,29 @@ public function testMixed(): void
 		]);
 	}
 
+	public function testOffsetAccessLegal(): void
+	{
+		$this->checkExplicitMixed = true;
+		$this->analyse([__DIR__ . '/data/offset-access-legal.php'], [
+			[
+				'Cannot access offset 0 on Closure(): void.',
+				7,
+			],
+			[
+				'Cannot access offset 0 on stdClass.',
+				12,
+			],
+			[
+				'Cannot access offset 0 on array{\'test\'}|stdClass.',
+				96,
+			],
+			[
+				'Cannot access offset 0 on array{\'test\'}|(Closure(): void).',
+				98,
+			],
+		]);
+	}
+
 	public function dataReportPossiblyNonexistentArrayOffset(): iterable
 	{
 		yield [false, false, []];

tests/PHPStan/Rules/Arrays/data/offset-access-legal.php

@@ -0,0 +1,99 @@
+<?php declare(strict_types=1); // lint >= 8.0
+
+namespace OffsetAccessLegal;
+
+function closure(): void
+{
+	(function(){})[0] ?? "error";
+}
+
+function nonArrayAccessibleObject()
+{
+	(new \stdClass())[0] ?? "error";
+}
+
+function arrayAccessibleObject()
+{
+	(new class implements \ArrayAccess {
+		public function offsetExists($offset) {
+			return true;
+		}
+
+		public function offsetGet($offset) {
+			return $offset;
+		}
+
+		public function offsetSet($offset, $value) {
+		}
+
+		public function offsetUnset($offset) {
+		}
+	})[0] ?? "error";
+}
+
+function array_(): void
+{
+	[0][0] ?? "error";
+}
+
+function integer(): void
+{
+	(0)[0] ?? 'ok';
+}
+
+function float(): void
+{
+	(0.0)[0] ?? 'ok';
+}
+
+function null(): void
+{
+	(null)[0] ?? 'ok';
+}
+
+function bool(): void
+{
+	(true)[0] ?? 'ok';
+}
+
+function void(): void
+{
+	((function (){})())[0] ?? 'ok';
+}
+
+function resource(): void
+{
+	(tmpfile())[0] ?? 'ok';
+}
+
+function offsetAccessibleMaybeAndLegal(): void
+{
+	$arrayAccessible = rand() ? (new class implements \ArrayAccess {
+		public function offsetExists($offset) {
+			return true;
+		}
+
+		public function offsetGet($offset) {
+			return $offset;
+		}
+
+		public function offsetSet($offset, $value) {
+		}
+
+		public function offsetUnset($offset) {
+		}
+	}) : false;
+
+	($arrayAccessible)[0] ?? "error";
+
+	(rand() ? "string" : true)[0] ?? "error";
+}
+
+function offsetAccessibleMaybeAndIllegal(): void
+{
+	$arrayAccessible = rand() ? new \stdClass() : ['test'];
+
+	($arrayAccessible)[0] ?? "error";
+
+	(rand() ? function(){} : ['test'])[0] ?? "error";
+}