Fix phpstan/phpstan#13799: false positive on in_array(...) check with impure second argument

src/Rules/Comparison/ImpossibleCheckTypeHelper.php

@@ -141,6 +141,11 @@ public function findSpecifiedType(
 
 							return null;
 						}
+
+						if (!$isNeedleSupertype->no()) {
+							// Array might be empty, so in_array can return false
+							return null;
+						}
 					}
 
 					if (!$haystackType instanceof ConstantArrayType || count($haystackType->getValueTypes()) > 0) {

tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php

@@ -1195,4 +1195,16 @@ public function testBug13566(): void
 		]);
 	}
 
+	public function testBug13799(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-13799.php'], [
+			[
+				'Call to function in_array() with arguments \'c\', list<\'a\'|\'b\'> and true will always evaluate to false.',
+				24,
+				'Because the type is coming from a PHPDoc, you can turn off this check by setting <fg=cyan>treatPhpDocTypesAsCertain: false</> in your <fg=cyan>%configurationFile%</>.',
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Comparison/data/bug-13799.php

@@ -0,0 +1,26 @@
+<?php declare(strict_types = 1);
+
+namespace Bug13799;
+
+/**
+ * @phpstan-impure
+ * @return list<'a'|'b'>
+ */
+function get_whitelist(): array {
+	$s = [];
+	if (rand(0, 1)) {
+		$s[] = 'a';
+	}
+	if (rand(0, 1)) {
+		$s[] = 'b';
+	}
+	return $s;
+}
+
+if (in_array('a', get_whitelist(), true)) {
+	echo 'ok';
+}
+
+if (in_array('c', get_whitelist(), true)) {
+	echo 'ok';
+}