[DeadCode] Skip fluent no return type on RemoveUnusedPrivateMethodRec…

…tor (#6108)

* [DeadCode] Skip fluent no return type on RemoveUnusedPrivateMethodRector

* comment

rules-tests/DeadCode/Rector/ClassMethod/RemoveUnusedPrivateMethodRector/Fixture/skip_fluent_no_return_type.php.inc

@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\Tests\DeadCode\Rector\ClassMethod\RemoveUnusedPrivateMethodRector\Fixture;
+
+class SkipFluentNoReturnType
+{
+    public function foo()
+    {
+        return $this
+            ->bar()
+            ->baz()
+            ->qux();
+    }
+
+    private function bar()
+    {
+        return $this;
+    }
+
+    private function baz()
+    {
+        return $this;
+    }
+
+    public function qux()
+    {
+        return $this;
+    }
+}

rules/DeadCode/NodeAnalyzer/CallCollectionAnalyzer.php

@@ -9,6 +9,8 @@
 use PhpParser\Node\Expr\StaticCall;
 use PhpParser\Node\Identifier;
 use PhpParser\Node\Name;
+use PHPStan\Type\MixedType;
+use PHPStan\Type\ThisType;
 use PHPStan\Type\TypeWithClassName;
 use Rector\Enum\ObjectReference;
 use Rector\NodeNameResolver\NodeNameResolver;
@@ -32,6 +34,20 @@ public function isExists(array $calls, string $classMethodName, string $classNam
             $callerType = $this->nodeTypeResolver->getType($callerRoot);
 
             if (! $callerType instanceof TypeWithClassName) {
+                // handle fluent by $this->bar()->baz()->qux()
+                // that methods don't have return type
+                if ($callerType instanceof MixedType && ! $callerType->isExplicitMixed()) {
+                    $cloneCallerRoot = clone $callerRoot;
+                    while ($cloneCallerRoot instanceof MethodCall && $cloneCallerRoot->var instanceof MethodCall) {
+                        $callerType = $this->nodeTypeResolver->getType($cloneCallerRoot->var->var);
+                        $cloneCallerRoot = $cloneCallerRoot->var;
+
+                        if ($callerType instanceof ThisType && $callerType->getStaticObjectType()->getClassName() === $className) {
+                            return true;
+                        }
+                    }
+                }
+
                 continue;
             }