[Configuration] Report explicit error when --only rule exists but is not registered

src/Configuration/OnlyRuleResolver.php

@@ -4,6 +4,7 @@
 
 namespace Rector\Configuration;
 
+use PHPStan\Reflection\ReflectionProvider;
 use Rector\Contract\Rector\RectorInterface;
 use Rector\Exception\Configuration\RectorRuleNameAmbiguousException;
 use Rector\Exception\Configuration\RectorRuleNotFoundException;
@@ -17,7 +18,8 @@
      * @param RectorInterface[] $rectors
      */
     public function __construct(
-        private array $rectors
+        private array $rectors,
+        private ReflectionProvider $reflectionProvider
     ) {
     }
 
@@ -82,6 +84,11 @@ public function resolve(string $rule): string
                 PHP_EOL
             );
         } else {
+            // the rule class exists, it is just missing in the config
+            if ($this->isRectorRuleClass($rule)) {
+                throw new RectorRuleNotFoundException($this->createUnregisteredMessage($rule));
+            }
+
             $message = sprintf(
                 'Rule "%s" was not found.%sMake sure it is registered in your config or in one of the sets',
                 $rule,
@@ -91,4 +98,34 @@ public function resolve(string $rule): string
 
         throw new RectorRuleNotFoundException($message);
     }
+
+    /**
+     * Is this an existing rule class, that is just not registered in the config?
+     */
+    private function isRectorRuleClass(string $className): bool
+    {
+        if (! $this->reflectionProvider->hasClass($className)) {
+            return false;
+        }
+
+        $classReflection = $this->reflectionProvider->getClass($className);
+        if ($classReflection->isAbstract()) {
+            return false;
+        }
+
+        return $classReflection->implementsInterface(RectorInterface::class);
+    }
+
+    private function createUnregisteredMessage(string $ruleClass): string
+    {
+        $shortRuleClass = substr((string) strrchr($ruleClass, '\\'), 1);
+
+        return sprintf(
+            'Rule "%s" exists, but is not registered in your Rector config.%sRegister it in your rector.php:'
+                . PHP_EOL . PHP_EOL . '    ->withRules([%s::class])',
+            $ruleClass,
+            PHP_EOL,
+            $shortRuleClass
+        );
+    }
 }

tests/Configuration/OnlyRuleResolverTest.php

@@ -4,13 +4,15 @@
 
 namespace Rector\Tests\Configuration;
 
+use PHPStan\Reflection\ReflectionProvider;
 use Rector\Configuration\OnlyRuleResolver;
 use Rector\Contract\Rector\RectorInterface;
 use Rector\DeadCode\Rector\Assign\RemoveDoubleAssignRector;
 use Rector\DeadCode\Rector\ClassMethod\RemoveUnusedPrivateMethodRector;
 use Rector\Exception\Configuration\RectorRuleNameAmbiguousException;
 use Rector\Exception\Configuration\RectorRuleNotFoundException;
 use Rector\Testing\PHPUnit\AbstractLazyTestCase;
+use Rector\TypeDeclaration\Rector\StmtsAwareInterface\SafeDeclareStrictTypesRector;
 
 final class OnlyRuleResolverTest extends AbstractLazyTestCase
 {
@@ -23,9 +25,10 @@ protected function setUp(): void
         $this->bootFromConfigFiles([__DIR__ . '/config/only_rule_resolver_config.php']);
         $rectorConfig = self::getContainer();
 
-        $this->onlyRuleResolver = new OnlyRuleResolver(iterator_to_array(
-            $rectorConfig->tagged(RectorInterface::class)
-        ));
+        $this->onlyRuleResolver = new OnlyRuleResolver(
+            iterator_to_array($rectorConfig->tagged(RectorInterface::class)),
+            $this->make(ReflectionProvider::class)
+        );
     }
 
     public function testResolveOk(): void
@@ -109,6 +112,18 @@ public function testResolveShortOkTwoLevels(): void
         );
     }
 
+    public function testResolveExistingButNotRegistered(): void
+    {
+        $this->expectExceptionMessageIsOrContains(
+            'Rule "Rector\TypeDeclaration\Rector\StmtsAwareInterface\SafeDeclareStrictTypesRector" exists, but is not registered in your Rector config.'
+                . PHP_EOL . 'Register it in your rector.php:' . PHP_EOL . PHP_EOL
+                . '    ->withRules([SafeDeclareStrictTypesRector::class])'
+        );
+        $this->expectException(RectorRuleNotFoundException::class);
+
+        $this->onlyRuleResolver->resolve(SafeDeclareStrictTypesRector::class);
+    }
+
     public function testResolveShortAmbiguous(): void
     {
         $this->expectExceptionMessageIsOrContains(