Fix phpstan/phpstan#10820: The playground reports false positives about changing the return type to never

src/Rules/Playground/MethodNeverRule.php

@@ -33,6 +33,10 @@ public function processNode(Node $node, Scope $scope): array
 
 		$method = $node->getMethodReflection();
 
+		if (!$method->isPrivate() && !$node->getClassReflection()->isFinal()) {
+			return [];
+		}
+
 		$returnType = $method->getReturnType();
 		$helperResult = $this->helper->shouldReturnNever($node, $returnType);
 		if ($helperResult === false) {

tests/PHPStan/Rules/Playground/MethodNeverRuleTest.php

@@ -36,4 +36,18 @@ public function testRule(): void
 		]);
 	}
 
+	public function testBug10820(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-10820.php'], [
+			[
+				'Method Bug10820\NonFinalBase::doPrivate() always throws an exception, it should have return type "never".',
+				28,
+			],
+			[
+				'Method Bug10820\FinalClass::doSomething() always throws an exception, it should have return type "never".',
+				36,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Playground/data/bug-10820.php

@@ -0,0 +1,40 @@
+<?php declare(strict_types = 1);
+
+namespace Bug10820;
+
+abstract class Value
+{
+    public function assertString(): SassString
+    {
+        throw new \Exception('this is not a string');
+    }
+}
+
+final class SassString extends Value
+{
+    public function assertString(): SassString
+    {
+        return $this;
+    }
+}
+
+class NonFinalBase
+{
+    protected function doSomething(): int
+    {
+        throw new \Exception('not implemented');
+    }
+
+    private function doPrivate(): int
+    {
+        throw new \Exception('not implemented');
+    }
+}
+
+final class FinalClass
+{
+    public function doSomething(): int
+    {
+        throw new \Exception('not implemented');
+    }
+}

tests/PHPStan/Rules/Playground/data/method-never.php

@@ -2,7 +2,7 @@
 
 namespace MethodNever;
 
-class Foo
+final class Foo
 {
 
 	public function doFoo(): never