Report error when using enum case outside of enum

- Added new EnumCaseOutsideEnumRule that reports an error when `case` is used in classes or interfaces instead of enums
- New regression test in tests/PHPStan/Rules/EnumCases/data/bug-14252.php
- The rule is registered at level 0 and uses the identifier `enum.caseOutsideOfEnum`

Closes phpstan/phpstan#14252

Author: phpstan-bot

src/Rules/EnumCases/EnumCaseOutsideEnumRule.php

@@ -0,0 +1,42 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\EnumCases;
+
+use PhpParser\Node;
+use PHPStan\Analyser\Scope;
+use PHPStan\DependencyInjection\RegisteredRule;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleErrorBuilder;
+
+/**
+ * @implements Rule<Node\Stmt\EnumCase>
+ */
+#[RegisteredRule(level: 0)]
+final class EnumCaseOutsideEnumRule implements Rule
+{
+
+	public function getNodeType(): string
+	{
+		return Node\Stmt\EnumCase::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		if (!$scope->isInClass()) {
+			return [];
+		}
+
+		$classReflection = $scope->getClassReflection();
+		if ($classReflection->isEnum()) {
+			return [];
+		}
+
+		return [
+			RuleErrorBuilder::message('Enum case can only be used in enums.')
+				->nonIgnorable()
+				->identifier('enum.caseOutsideOfEnum')
+				->build(),
+		];
+	}
+
+}

tests/PHPStan/Rules/EnumCases/EnumCaseOutsideEnumRuleTest.php

@@ -0,0 +1,35 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\EnumCases;
+
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+use PHPUnit\Framework\Attributes\RequiresPhp;
+
+/**
+ * @extends RuleTestCase<EnumCaseOutsideEnumRule>
+ */
+class EnumCaseOutsideEnumRuleTest extends RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return new EnumCaseOutsideEnumRule();
+	}
+
+	#[RequiresPhp('>= 8.1')]
+	public function testRule(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-14252.php'], [
+			[
+				'Enum case can only be used in enums.',
+				9,
+			],
+			[
+				'Enum case can only be used in enums.',
+				14,
+			],
+		]);
+	}
+
+}

tests/PHPStan/Rules/EnumCases/data/bug-14252.php

@@ -0,0 +1,20 @@
+<?php // lint >= 8.1
+
+declare(strict_types = 1);
+
+namespace Bug14252;
+
+class Foo
+{
+	case Active;
+}
+
+interface Bar
+{
+	case Active;
+}
+
+enum Qux
+{
+	case Active;
+}